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A dive into the PE file format - PE file structure - Part 4: Data Directories, Section Headers and Sections

✇0xRick
By: 0xRick
27 October 2021 at 01:00

A dive into the PE file format - PE file structure - Part 4: Data Directories, Section Headers and Sections

Introduction

In the last post we talked about the NT Headers and we skipped the last part of the Optional Header which was the data directories.

In this post we’re going to talk about what data directories are and where they are located.
We’re also going to cover section headers and sections in this post.

Data Directories

The last member of the IMAGE_OPTIONAL_HEADER structure was an array of IMAGE_DATA_DIRECTORY structures defined as follows:

IMAGE_DATA_DIRECTORY DataDirectory[IMAGE_NUMBEROF_DIRECTORY_ENTRIES];

IMAGE_NUMBEROF_DIRECTORY_ENTRIES is a constant defined with the value 16, meaning that this array can have up to 16 IMAGE_DATA_DIRECTORY entries:

#define IMAGE_NUMBEROF_DIRECTORY_ENTRIES    16

An IMAGE_DATA_DIRETORY structure is defines as follows:

typedef struct _IMAGE_DATA_DIRECTORY {
    DWORD   VirtualAddress;
    DWORD   Size;
} IMAGE_DATA_DIRECTORY, *PIMAGE_DATA_DIRECTORY;

It’s a very simple structure with only two members, first one being an RVA pointing to the start of the Data Directory and the second one being the size of the Data Directory.

So what is a Data Directory? Basically a Data Directory is a piece of data located within one of the sections of the PE file.
Data Directories contain useful information needed by the loader, an example of a very important directory is the Import Directory which contains a list of external functions imported from other libraries, we’ll discuss it in more detail when we go over PE imports.

Please note that not all Data Directories have the same structure, the IMAGE_DATA_DIRECTORY.VirtualAddress points to the Data Directory, however the type of that directory is what determines how that chunk of data is going to be parsed.

Here’s a list of Data Directories defined in winnt.h. (Each one of these values represents an index in the DataDirectory array):

// Directory Entries

#define IMAGE_DIRECTORY_ENTRY_EXPORT          0   // Export Directory
#define IMAGE_DIRECTORY_ENTRY_IMPORT          1   // Import Directory
#define IMAGE_DIRECTORY_ENTRY_RESOURCE        2   // Resource Directory
#define IMAGE_DIRECTORY_ENTRY_EXCEPTION       3   // Exception Directory
#define IMAGE_DIRECTORY_ENTRY_SECURITY        4   // Security Directory
#define IMAGE_DIRECTORY_ENTRY_BASERELOC       5   // Base Relocation Table
#define IMAGE_DIRECTORY_ENTRY_DEBUG           6   // Debug Directory
//      IMAGE_DIRECTORY_ENTRY_COPYRIGHT       7   // (X86 usage)
#define IMAGE_DIRECTORY_ENTRY_ARCHITECTURE    7   // Architecture Specific Data
#define IMAGE_DIRECTORY_ENTRY_GLOBALPTR       8   // RVA of GP
#define IMAGE_DIRECTORY_ENTRY_TLS             9   // TLS Directory
#define IMAGE_DIRECTORY_ENTRY_LOAD_CONFIG    10   // Load Configuration Directory
#define IMAGE_DIRECTORY_ENTRY_BOUND_IMPORT   11   // Bound Import Directory in headers
#define IMAGE_DIRECTORY_ENTRY_IAT            12   // Import Address Table
#define IMAGE_DIRECTORY_ENTRY_DELAY_IMPORT   13   // Delay Load Import Descriptors
#define IMAGE_DIRECTORY_ENTRY_COM_DESCRIPTOR 14   // COM Runtime descriptor

If we take a look at the contents of IMAGE_OPTIONAL_HEADER.DataDirectory of an actual PE file, we might see entries where both fields are set to 0:

This means that this specific Data Directory is not used (doesn’t exist) in the executable file.

Sections and Section Headers

Sections

Sections are the containers of the actual data of the executable file, they occupy the rest of the PE file after the headers, precisely after the section headers.
Some sections have special names that indicate their purpose, we’ll go over some of them, and a full list of these names can be found on the official Microsoft documentation under the “Special Sections” section.

  • .text: Contains the executable code of the program.
  • .data: Contains the initialized data.
  • .bss: Contains uninitialized data.
  • .rdata: Contains read-only initialized data.
  • .edata: Contains the export tables.
  • .idata: Contains the import tables.
  • .reloc: Contains image relocation information.
  • .rsrc: Contains resources used by the program, these include images, icons or even embedded binaries.
  • .tls: (Thread Local Storage), provides storage for every executing thread of the program.

Section Headers

After the Optional Header and before the sections comes the Section Headers. These headers contain information about the sections of the PE file.

A Section Header is a structure named IMAGE_SECTION_HEADER defined in winnt.h as follows:

typedef struct _IMAGE_SECTION_HEADER {
    BYTE    Name[IMAGE_SIZEOF_SHORT_NAME];
    union {
            DWORD   PhysicalAddress;
            DWORD   VirtualSize;
    } Misc;
    DWORD   VirtualAddress;
    DWORD   SizeOfRawData;
    DWORD   PointerToRawData;
    DWORD   PointerToRelocations;
    DWORD   PointerToLinenumbers;
    WORD    NumberOfRelocations;
    WORD    NumberOfLinenumbers;
    DWORD   Characteristics;
} IMAGE_SECTION_HEADER, *PIMAGE_SECTION_HEADER;
  • Name: First field of the Section Header, a byte array of the size IMAGE_SIZEOF_SHORT_NAME that holds the name of the section. IMAGE_SIZEOF_SHORT_NAME has the value of 8 meaning that a section name can’t be longer than 8 characters. For longer names the official documentation mentions a work-around by filling this field with an offset in the string table, however executable images do not use a string table so this limitation of 8 characters holds for executable images.
  • PhysicalAddress or VirtualSize: A union defines multiple names for the same thing, this field contains the total size of the section when it’s loaded in memory.
  • VirtualAddress: The documentation states that for executable images this field holds the address of the first byte of the section relative to the image base when loaded in memory, and for object files it holds the address of the first byte of the section before relocation is applied.
  • SizeOfRawData: This field contains the size of the section on disk, it must be a multiple of IMAGE_OPTIONAL_HEADER.FileAlignment.
    SizeOfRawData and VirtualSize can be different, we’ll discuss the reason for this later in the post.
  • PointerToRawData: A pointer to the first page of the section within the file, for executable images it must be a multiple of IMAGE_OPTIONAL_HEADER.FileAlignment.
  • PointerToRelocations: A file pointer to the beginning of relocation entries for the section. It’s set to 0 for executable files.
  • PointerToLineNumbers: A file pointer to the beginning of COFF line-number entries for the section. It’s set to 0 because COFF debugging information is deprecated.
  • NumberOfRelocations: The number of relocation entries for the section, it’s set to 0 for executable images.
  • NumberOfLinenumbers: The number of COFF line-number entries for the section, it’s set to 0 because COFF debugging information is deprecated.
  • Characteristics: Flags that describe the characteristics of the section.
    These characteristics are things like if the section contains executable code, contains initialized/uninitialized data, can be shared in memory.
    A complete list of section characteristics flags can be found on the official Microsoft documentation.

SizeOfRawData and VirtualSize can be different, and this can happen for multiple of reasons.

SizeOfRawData must be a multiple of IMAGE_OPTIONAL_HEADER.FileAlignment, so if the section size is less than that value the rest gets padded and SizeOfRawData gets rounded to the nearest multiple of IMAGE_OPTIONAL_HEADER.FileAlignment.
However when the section is loaded into memory it doesn’t follow that alignment and only the actual size of the section is occupied.
In this case SizeOfRawData will be greater than VirtualSize

The opposite can happen as well.
If the section contains uninitialized data, these data won’t be accounted for on disk, but when the section gets mapped into memory, the section will expand to reserve memory space for when the uninitialized data gets later initialized and used.
This means that the section on disk will occupy less than it will do in memory, in this case VirtualSize will be greater than SizeOfRawData.

Here’s the view of Section Headers in PE-bear:

We can see Raw Addr. and Virtual Addr. fields which correspond to IMAGE_SECTION_HEADER.PointerToRawData and IMAGE_SECTION_HEADER.VirtualAddress.

Raw Size and Virtual Size correspond to IMAGE_SECTION_HEADER.SizeOfRawData and IMAGE_SECTION_HEADER.VirtualSize.
We can see how these two fields are used to calculate where the section ends, both on disk and in memory.
For example if we take the .text section, it has a raw address of 0x400 and a raw size of 0xE00, if we add them together we get 0x1200 which is displayed as the section end on disk.
Similarly we can do the same with virtual size and address, virtual address is 0x1000 and virtual size is 0xD2C, if we add them together we get 0x1D2C.

The Characteristics field marks some sections as read-only, some other sections as read-write and some sections as readable and executable.

PointerToRelocations, NumberOfRelocations and NumberOfLinenumbers are set to 0 as expected.

Conclusion

That’s it for this post, we’ve discussed what Data Directories are and we talked about sections.
The next post will be about PE imports.
Thanks for reading.

A dive into the PE file format - PE file structure - Part 5: PE Imports (Import Directory Table, ILT, IAT)

✇0xRick
By: 0xRick
28 October 2021 at 01:00

A dive into the PE file format - PE file structure - Part 5: PE Imports (Import Directory Table, ILT, IAT)

Introduction

In this post we’re going to talk about a very important aspect of PE files, the PE imports. To understand how PE files handle their imports, we’ll go over some of the Data Directories present in the Import Data section (.idata), the Import Directory Table, the Import Lookup Table (ILT) or also referred to as the Import Name Table (INT) and the Import Address Table (IAT).

Import Directory Table

The Import Directory Table is a Data Directory located at the beginning of the .idata section.

It consists of an array of IMAGE_IMPORT_DESCRIPTOR structures, each one of them is for a DLL.
It doesn’t have a fixed size, so the last IMAGE_IMPORT_DESCRIPTOR of the array is zeroed-out (NULL-Padded) to indicate the end of the Import Directory Table.

IMAGE_IMPORT_DESCRIPTOR is defined as follows:

typedef struct _IMAGE_IMPORT_DESCRIPTOR {
    union {
        DWORD   Characteristics;
        DWORD   OriginalFirstThunk;
    } DUMMYUNIONNAME;
    DWORD   TimeDateStamp;
    DWORD   ForwarderChain;
    DWORD   Name;
    DWORD   FirstThunk;
} IMAGE_IMPORT_DESCRIPTOR;
typedef IMAGE_IMPORT_DESCRIPTOR UNALIGNED *PIMAGE_IMPORT_DESCRIPTOR;
  • OriginalFirstThunk: RVA of the ILT.
  • TimeDateStamp: A time date stamp, that’s initially set to 0 if not bound and set to -1 if bound.
    In case of an unbound import the time date stamp gets updated to the time date stamp of the DLL after the image is bound.
    In case of a bound import it stays set to -1 and the real time date stamp of the DLL can be found in the Bound Import Directory Table in the corresponding IMAGE_BOUND_IMPORT_DESCRIPTOR .
    We’ll discuss bound imports in the next section.
  • ForwarderChain: The index of the first forwarder chain reference.
    This is something responsible for DLL forwarding. (DLL forwarding is when a DLL forwards some of its exported functions to another DLL.)
  • Name: An RVA of an ASCII string that contains the name of the imported DLL.
  • FirstThunk: RVA of the IAT.

Bound Imports

A bound import essentially means that the import table contains fixed addresses for the imported functions.
These addresses are calculated and written during compile time by the linker.

Using bound imports is a speed optimization, it reduces the time needed by the loader to resolve function addresses and fill the IAT, however if at run-time the bound addresses do not match the real ones then the loader will have to resolve these addresses again and fix the IAT.

When discussing IMAGE_IMPORT_DESCRIPTOR.TimeDateStamp, I mentioned that in case of a bound import, the time date stamp is set to -1 and the real time date stamp of the DLL can be found in the corresponding IMAGE_BOUND_IMPORT_DESCRIPTOR in the Bound Import Data Directory.

Bound Import Data Directory

The Bound Import Data Directory is similar to the Import Directory Table, however as the name suggests, it holds information about the bound imports.

It consists of an array of IMAGE_BOUND_IMPORT_DESCRIPTOR structures, and ends with a zeroed-out IMAGE_BOUND_IMPORT_DESCRIPTOR.

IMAGE_BOUND_IMPORT_DESCRIPTOR is defined as follows:

typedef struct _IMAGE_BOUND_IMPORT_DESCRIPTOR {
    DWORD   TimeDateStamp;
    WORD    OffsetModuleName;
    WORD    NumberOfModuleForwarderRefs;
// Array of zero or more IMAGE_BOUND_FORWARDER_REF follows
} IMAGE_BOUND_IMPORT_DESCRIPTOR,  *PIMAGE_BOUND_IMPORT_DESCRIPTOR;
  • TimeDateStamp: The time date stamp of the imported DLL.
  • OffsetModuleName: An offset to a string with the name of the imported DLL.
    It’s an offset from the first IMAGE_BOUND_IMPORT_DESCRIPTOR
  • NumberOfModuleForwarderRefs: The number of the IMAGE_BOUND_FORWARDER_REF structures that immediately follow this structure.
    IMAGE_BOUND_FORWARDER_REF is a structure that’s identical to IMAGE_BOUND_IMPORT_DESCRIPTOR, the only difference is that the last member is reserved.

That’s all we need to know about bound imports.

Import Lookup Table (ILT)

Sometimes people refer to it as the Import Name Table (INT).

Every imported DLL has an Import Lookup Table.
IMAGE_IMPORT_DESCRIPTOR.OriginalFirstThunk holds the RVA of the ILT of the corresponding DLL.

The ILT is essentially a table of names or references, it tells the loader which functions are needed from the imported DLL.

The ILT consists of an array of 32-bit numbers (for PE32) or 64-bit numbers for (PE32+), the last one is zeroed-out to indicate the end of the ILT.

Each entry of these entries encodes information as follows:

  • Bit 31/63 (most significant bit): This is called the Ordinal/Name flag, it specifies whether to import the function by name or by ordinal.
  • Bits 15-0: If the Ordinal/Name flag is set to 1 these bits are used to hold the 16-bit ordinal number that will be used to import the function, bits 30-15/62-15 for PE32/PE32+ must be set to 0.
  • Bits 30-0: If the Ordinal/Name flag is set to 0 these bits are used to hold an RVA of a Hint/Name table.

Hint/Name Table

A Hint/Name table is a structure defined in winnt.h as IMAGE_IMPORT_BY_NAME:

typedef struct _IMAGE_IMPORT_BY_NAME {
    WORD    Hint;
    CHAR   Name[1];
} IMAGE_IMPORT_BY_NAME, *PIMAGE_IMPORT_BY_NAME;
  • Hint: A word that contains a number, this number is used to look-up the function, that number is first used as an index into the export name pointer table, if that initial check fails a binary search is performed on the DLL’s export name pointer table.
  • Name: A null-terminated string that contains the name of the function to import.

Import Address Table (IAT)

On disk, the IAT is identical to the ILT, however during bounding when the binary is being loaded into memory, the entries of the IAT get overwritten with the addresses of the functions that are being imported.

Summary

So to summarize what we discussed in this post, for every DLL the executable is loading functions from, there will be an IMAGE_IMPORT_DESCRIPTOR within the Image Directory Table.
The IMAGE_IMPORT_DESCRIPTOR will contain the name of the DLL, and two fields holding RVAs of the ILT and the IAT.
The ILT will contain references for all the functions that are being imported from the DLL.
The IAT will be identical to the ILT until the executable is loaded in memory, then the loader will fill the IAT with the actual addresses of the imported functions.
If the DLL import is a bound import, then the import information will be contained in IMAGE_BOUND_IMPORT_DESCRIPTOR structures in a separate Data Directory called the Bound Import Data Directory.

Let’s take a quick look at the import information inside of an actual PE file.

Here’s the Import Directory Table of the executable:

All of these entries are IMAGE_IMPORT_DESCRIPTORs.

As you can see, the TimeDateStamp of all the imports is set to 0, meaning that none of these imports are bound, this is also confirmed in the Bound? column added by PE-bear.

For example, if we take USER32.dll and follow the RVA of its ILT (referenced by OriginalFirstThunk), we’ll find only 1 entry (because only one function is imported), and that entry looks like this:

This is a 64-bit executable, so the entry is 64 bits long.
As you can see, the last byte is set to 0, indicating that a Hint/Table name should be used to look-up the function.
We know that the RVA of this Hint/Table name should be referenced by the first 2 bytes, so we should follow RVA 0x29F8:

Now we’re looking at an IMAGE_IMPORT_BY_NAME structure, first two bytes hold the hint, which in this case is 0x283, the rest of the structure holds the full name of the function which is MessageBoxA.
We can verify that our interpretation of the data is correct by looking at how PE-bear parsed it, and we’ll see the same results:

Conclusion

That’s all I have to say about PE imports, in the next post I’ll discuss PE base relocations.
Thanks for reading.

A dive into the PE file format - PE file structure - Part 6: PE Base Relocations

✇0xRick
By: 0xRick
28 October 2021 at 15:00

A dive into the PE file format - PE file structure - Part 6: PE Base Relocations

Introduction

In this post we’re going to talk about PE base relocations. We’re going to discuss what relocations are, then we’ll take a look at the relocation table.

Relocations

When a program is compiled, the compiler assumes that the executable is going to be loaded at a certain base address, that address is saved in IMAGE_OPTIONAL_HEADER.ImageBase, some addresses get calculated then hardcoded within the executable based on the base address.
However for a variety of reasons, it’s not very likely that the executable is going to get its desired base address, it will get loaded in another base address and that will make all of the hardcoded addresses invalid.
A list of all hardcoded values that will need fixing if the image is loaded at a different base address is saved in a special table called the Relocation Table (a Data Directory within the .reloc section). The process of relocating (done by the loader) is what fixes these values.

Let’s take an example, the following code defines an int variable and a pointer to that variable:

int test = 2;
int* testPtr = &test;

During compile-time, the compiler will assume a base address, let’s say it assumes a base address of 0x1000, it decides that test will be located at an offset of 0x100 and based on that it gives testPtr a value of 0x1100.
Later on, a user runs the program and the image gets loaded into memory.
It gets a base address of 0x2000, this means that the hardcoded value of testPtr will be invalid, the loader fixes that value by adding the difference between the assumed base address and the actual base address, in this case it’s a difference of 0x1000 (0x2000 - 0x1000), so the new value of testPtr will be 0x2100 (0x1100 + 0x1000) which is the correct new address of test.

Relocation Table

As described by Microsoft documentation, the base relocation table contains entries for all base relocations in the image.

It’s a Data Directory located within the .reloc section, it’s divided into blocks, each block represents the base relocations for a 4K page and each block must start on a 32-bit boundary.

Each block starts with an IMAGE_BASE_RELOCATION structure followed by any number of offset field entries.

The IMAGE_BASE_RELOCATION structure specifies the page RVA, and the size of the relocation block.

typedef struct _IMAGE_BASE_RELOCATION {
    DWORD   VirtualAddress;
    DWORD   SizeOfBlock;
} IMAGE_BASE_RELOCATION;
typedef IMAGE_BASE_RELOCATION UNALIGNED * PIMAGE_BASE_RELOCATION;

Each offset field entry is a WORD, first 4 bits of it define the relocation type (check Microsoft documentation for a list of relocation types), the last 12 bits store an offset from the RVA specified in the IMAGE_BASE_RELOCATION structure at the start of the relocation block.

Each relocation entry gets processed by adding the RVA of the page to the image base address, then by adding the offset specified in the relocation entry, an absolute address of the location that needs fixing can be obtained.

The PE file I’m looking at contains only one relocation block, its size is 0x28 bytes:

We know that each block starts with an 8-byte-long structure, meaning that the size of the entries is 0x20 bytes (32 bytes), each entry’s size is 2 bytes so the total number of entries should be 16.

Conclusion

That’s all.
Thanks for reading.

A dive into the PE file format - LAB 1: Writing a PE Parser

✇0xRick
By: 0xRick
29 October 2021 at 01:00

A dive into the PE file format - LAB 1: Writing a PE Parser

Introduction

In the previous posts we’ve discussed the basic structure of PE files, In this post we’re going to apply this knowledge into building a PE file parser in c++ as a proof of concept.

The parser we’re going to build will not be a full parser and is not intended to be used as a reliable tool, this is only an exercise to better understand the PE file structure.
We’re going to focus on PE32 and PE32+ files, and we’ll only parse the following parts of the file:

  • DOS Header
  • Rich Header
  • NT Headers
  • Data Directories (within the Optional Header)
  • Section Headers
  • Import Table
  • Base Relocations Table

The code of this project can be found on my github profile.

Initial Setup

Process Outline

We want out parser to follow the following process:

  1. Read a file.
  2. Validate that it’s a PE file.
  3. Determine whether it’s a PE32 or a PE32+.
  4. Parse out the following structures:
    • DOS Header
    • Rich Header
    • NT Headers
    • Section Headers
    • Import Data Directory
    • Base Relocation Data Directory
  5. Print out the following information:
    • File name and type.
    • DOS Header:
      • Magic value.
      • Address of new exe header.
    • Each entry of the Rich Header, decrypted and decoded.
    • NT Headers - PE file signature.
    • NT Headers - File Header:
      • Machine value.
      • Number of sections.
      • Size of Optional Header.
    • NT Headers - Optional Header:
      • Magic value.
      • Size of code section.
      • Size of initialized data.
      • Size of uninitialized data.
      • Address of entry point.
      • RVA of start of code section.
      • Desired Image Base.
      • Section alignment.
      • File alignment.
      • Size of image.
      • Size of headers.
    • For each Data Directory: its name, RVA and size.
    • For each Section Header:
      • Section name.
      • Section virtual address and size.
      • Section raw data pointer and size.
      • Section characteristics value.
    • Import Table:
      • For each DLL:
        • DLL name.
        • ILT and IAT RVAs.
        • Whether its a bound import or not.
        • for every imported function:
          • Ordinal if ordinal/name flag is 1.
          • Name, hint and Hint/Name table RVA if ordinal/name flag is 0.
    • Base Relocation Table:
      • For each block:
        • Page RVA.
        • Block size.
        • Number of entries.
        • For each entry:
          • Raw value.
          • Relocation offset.
          • Relocation Type.

winnt.h Definitions

We will need the following definitions from the winnt.h header:

  • Types:
    • BYTE
    • WORD
    • DWORD
    • QWORD
    • LONG
    • LONGLONG
    • ULONGLONG
  • Constants:
    • IMAGE_NT_OPTIONAL_HDR32_MAGIC
    • IMAGE_NT_OPTIONAL_HDR64_MAGIC
    • IMAGE_NUMBEROF_DIRECTORY_ENTRIES
    • IMAGE_DOS_SIGNATURE
    • IMAGE_DIRECTORY_ENTRY_EXPORT
    • IMAGE_DIRECTORY_ENTRY_IMPORT
    • IMAGE_DIRECTORY_ENTRY_RESOURCE
    • IMAGE_DIRECTORY_ENTRY_EXCEPTION
    • IMAGE_DIRECTORY_ENTRY_SECURITY
    • IMAGE_DIRECTORY_ENTRY_BASERELOC
    • IMAGE_DIRECTORY_ENTRY_DEBUG
    • IMAGE_DIRECTORY_ENTRY_ARCHITECTURE
    • IMAGE_DIRECTORY_ENTRY_GLOBALPTR
    • IMAGE_DIRECTORY_ENTRY_TLS
    • IMAGE_DIRECTORY_ENTRY_LOAD_CONFIG
    • IMAGE_DIRECTORY_ENTRY_BOUND_IMPORT
    • IMAGE_DIRECTORY_ENTRY_IAT
    • IMAGE_DIRECTORY_ENTRY_DELAY_IMPORT
    • IMAGE_DIRECTORY_ENTRY_COM_DESCRIPTOR
    • IMAGE_SIZEOF_SHORT_NAME
    • IMAGE_SIZEOF_SECTION_HEADER
  • Structures:
    • IMAGE_DOS_HEADER
    • IMAGE_DATA_DIRECTORY
    • IMAGE_OPTIONAL_HEADER32
    • IMAGE_OPTIONAL_HEADER64
    • IMAGE_FILE_HEADER
    • IMAGE_NT_HEADERS32
    • IMAGE_NT_HEADERS64
    • IMAGE_IMPORT_DESCRIPTOR
    • IMAGE_IMPORT_BY_NAME
    • IMAGE_BASE_RELOCATION
    • IMAGE_SECTION_HEADER

I took these definitions from winnt.h and added them to a new header called winntdef.h.

winntdef.h:

typedef unsigned char BYTE;
typedef unsigned short WORD;
typedef unsigned long DWORD;
typedef unsigned long long QWORD;
typedef unsigned long LONG;
typedef __int64 LONGLONG;
typedef unsigned __int64 ULONGLONG;

#define ___IMAGE_NT_OPTIONAL_HDR32_MAGIC       0x10b
#define ___IMAGE_NT_OPTIONAL_HDR64_MAGIC       0x20b
#define ___IMAGE_NUMBEROF_DIRECTORY_ENTRIES    16
#define ___IMAGE_DOS_SIGNATURE                 0x5A4D

#define ___IMAGE_DIRECTORY_ENTRY_EXPORT          0
#define ___IMAGE_DIRECTORY_ENTRY_IMPORT          1
#define ___IMAGE_DIRECTORY_ENTRY_RESOURCE        2
#define ___IMAGE_DIRECTORY_ENTRY_EXCEPTION       3
#define ___IMAGE_DIRECTORY_ENTRY_SECURITY        4
#define ___IMAGE_DIRECTORY_ENTRY_BASERELOC       5
#define ___IMAGE_DIRECTORY_ENTRY_DEBUG           6
#define ___IMAGE_DIRECTORY_ENTRY_ARCHITECTURE    7
#define ___IMAGE_DIRECTORY_ENTRY_GLOBALPTR       8
#define ___IMAGE_DIRECTORY_ENTRY_TLS             9
#define ___IMAGE_DIRECTORY_ENTRY_LOAD_CONFIG    10
#define ___IMAGE_DIRECTORY_ENTRY_BOUND_IMPORT   11
#define ___IMAGE_DIRECTORY_ENTRY_IAT            12
#define ___IMAGE_DIRECTORY_ENTRY_DELAY_IMPORT   13
#define ___IMAGE_DIRECTORY_ENTRY_COM_DESCRIPTOR 14

#define ___IMAGE_SIZEOF_SHORT_NAME              8
#define ___IMAGE_SIZEOF_SECTION_HEADER          40

typedef struct __IMAGE_DOS_HEADER {
    WORD   e_magic;
    WORD   e_cblp;
    WORD   e_cp;
    WORD   e_crlc;
    WORD   e_cparhdr;
    WORD   e_minalloc;
    WORD   e_maxalloc;
    WORD   e_ss;
    WORD   e_sp;
    WORD   e_csum;
    WORD   e_ip;
    WORD   e_cs;
    WORD   e_lfarlc;
    WORD   e_ovno;
    WORD   e_res[4];
    WORD   e_oemid;
    WORD   e_oeminfo;
    WORD   e_res2[10];
    LONG   e_lfanew;
} ___IMAGE_DOS_HEADER, * ___PIMAGE_DOS_HEADER;

typedef struct __IMAGE_DATA_DIRECTORY {
    DWORD   VirtualAddress;
    DWORD   Size;
} ___IMAGE_DATA_DIRECTORY, * ___PIMAGE_DATA_DIRECTORY;


typedef struct __IMAGE_OPTIONAL_HEADER {
    WORD    Magic;
    BYTE    MajorLinkerVersion;
    BYTE    MinorLinkerVersion;
    DWORD   SizeOfCode;
    DWORD   SizeOfInitializedData;
    DWORD   SizeOfUninitializedData;
    DWORD   AddressOfEntryPoint;
    DWORD   BaseOfCode;
    DWORD   BaseOfData;
    DWORD   ImageBase;
    DWORD   SectionAlignment;
    DWORD   FileAlignment;
    WORD    MajorOperatingSystemVersion;
    WORD    MinorOperatingSystemVersion;
    WORD    MajorImageVersion;
    WORD    MinorImageVersion;
    WORD    MajorSubsystemVersion;
    WORD    MinorSubsystemVersion;
    DWORD   Win32VersionValue;
    DWORD   SizeOfImage;
    DWORD   SizeOfHeaders;
    DWORD   CheckSum;
    WORD    Subsystem;
    WORD    DllCharacteristics;
    DWORD   SizeOfStackReserve;
    DWORD   SizeOfStackCommit;
    DWORD   SizeOfHeapReserve;
    DWORD   SizeOfHeapCommit;
    DWORD   LoaderFlags;
    DWORD   NumberOfRvaAndSizes;
    ___IMAGE_DATA_DIRECTORY DataDirectory[___IMAGE_NUMBEROF_DIRECTORY_ENTRIES];
} ___IMAGE_OPTIONAL_HEADER32, * ___PIMAGE_OPTIONAL_HEADER32;

typedef struct __IMAGE_OPTIONAL_HEADER64 {
    WORD        Magic;
    BYTE        MajorLinkerVersion;
    BYTE        MinorLinkerVersion;
    DWORD       SizeOfCode;
    DWORD       SizeOfInitializedData;
    DWORD       SizeOfUninitializedData;
    DWORD       AddressOfEntryPoint;
    DWORD       BaseOfCode;
    ULONGLONG   ImageBase;
    DWORD       SectionAlignment;
    DWORD       FileAlignment;
    WORD        MajorOperatingSystemVersion;
    WORD        MinorOperatingSystemVersion;
    WORD        MajorImageVersion;
    WORD        MinorImageVersion;
    WORD        MajorSubsystemVersion;
    WORD        MinorSubsystemVersion;
    DWORD       Win32VersionValue;
    DWORD       SizeOfImage;
    DWORD       SizeOfHeaders;
    DWORD       CheckSum;
    WORD        Subsystem;
    WORD        DllCharacteristics;
    ULONGLONG   SizeOfStackReserve;
    ULONGLONG   SizeOfStackCommit;
    ULONGLONG   SizeOfHeapReserve;
    ULONGLONG   SizeOfHeapCommit;
    DWORD       LoaderFlags;
    DWORD       NumberOfRvaAndSizes;
    ___IMAGE_DATA_DIRECTORY DataDirectory[___IMAGE_NUMBEROF_DIRECTORY_ENTRIES];
} ___IMAGE_OPTIONAL_HEADER64, * ___PIMAGE_OPTIONAL_HEADER64;

typedef struct __IMAGE_FILE_HEADER {
    WORD    Machine;
    WORD    NumberOfSections;
    DWORD   TimeDateStamp;
    DWORD   PointerToSymbolTable;
    DWORD   NumberOfSymbols;
    WORD    SizeOfOptionalHeader;
    WORD    Characteristics;
} ___IMAGE_FILE_HEADER, * ___PIMAGE_FILE_HEADER;

typedef struct __IMAGE_NT_HEADERS64 {
    DWORD Signature;
    ___IMAGE_FILE_HEADER FileHeader;
    ___IMAGE_OPTIONAL_HEADER64 OptionalHeader;
} ___IMAGE_NT_HEADERS64, * ___PIMAGE_NT_HEADERS64;

typedef struct __IMAGE_NT_HEADERS {
    DWORD Signature;
    ___IMAGE_FILE_HEADER FileHeader;
    ___IMAGE_OPTIONAL_HEADER32 OptionalHeader;
} ___IMAGE_NT_HEADERS32, * ___PIMAGE_NT_HEADERS32;

typedef struct __IMAGE_IMPORT_DESCRIPTOR {
    union {
        DWORD   Characteristics;
        DWORD   OriginalFirstThunk;
    } DUMMYUNIONNAME;
    DWORD   TimeDateStamp;
    DWORD   ForwarderChain;
    DWORD   Name;
    DWORD   FirstThunk;
} ___IMAGE_IMPORT_DESCRIPTOR, * ___PIMAGE_IMPORT_DESCRIPTOR;

typedef struct __IMAGE_IMPORT_BY_NAME {
    WORD    Hint;
    char   Name[100];
} ___IMAGE_IMPORT_BY_NAME, * ___PIMAGE_IMPORT_BY_NAME;

typedef struct __IMAGE_BASE_RELOCATION {
    DWORD   VirtualAddress;
    DWORD   SizeOfBlock;
} ___IMAGE_BASE_RELOCATION, * ___PIMAGE_BASE_RELOCATION;

typedef struct __IMAGE_SECTION_HEADER {
    BYTE    Name[___IMAGE_SIZEOF_SHORT_NAME];
    union {
        DWORD   PhysicalAddress;
        DWORD   VirtualSize;
    } Misc;
    DWORD   VirtualAddress;
    DWORD   SizeOfRawData;
    DWORD   PointerToRawData;
    DWORD   PointerToRelocations;
    DWORD   PointerToLinenumbers;
    WORD    NumberOfRelocations;
    WORD    NumberOfLinenumbers;
    DWORD   Characteristics;
} ___IMAGE_SECTION_HEADER, * ___PIMAGE_SECTION_HEADER;

Custom Structures

I defined the following structures to help with the parsing process. They’re defined in the PEFILE_CUSTOM_STRUCTS.h header.

RICH_HEADER_INFO

A structure to hold information about the Rich Header during processing.

typedef struct __RICH_HEADER_INFO {
    int size;
    char* ptrToBuffer;
    int entries;
} RICH_HEADER_INFO, * PRICH_HEADER_INFO;
  • size: Size of the Rich Header (in bytes).
  • ptrToBuffer: A pointer to the buffer containing the data of the Rich Header.
  • entries: Number of entries in the Rich Header.
RICH_HEADER_ENTRY

A structure to represent a Rich Header entry.

typedef struct __RICH_HEADER_ENTRY {
    WORD  prodID;
    WORD  buildID;
    DWORD useCount;
} RICH_HEADER_ENTRY, * PRICH_HEADER_ENTRY;
  • prodID: Type ID / Product ID.
  • buildID: Build ID.
  • useCount: Use count.
RICH_HEADER

A structure to represent the Rich Header.

typedef struct __RICH_HEADER {
    PRICH_HEADER_ENTRY entries;
} RICH_HEADER, * PRICH_HEADER;
  • entries: A pointer to a RICH_HEADER_ENTRY array.
ILT_ENTRY_32

A structure to represent a 32-bit ILT entry during processing.

typedef struct __ILT_ENTRY_32 {
    union {
        DWORD ORDINAL : 16;
        DWORD HINT_NAME_TABE : 32;
        DWORD ORDINAL_NAME_FLAG : 1;
    } FIELD_1;
} ILT_ENTRY_32, * PILT_ENTRY_32;

The structure will hold a 32-bit value and will return the appropriate piece of information (using bit fields) when the member corresponding to that piece of information is accessed.

ILT_ENTRY_64

A structure to represent a 64-bit ILT entry during processing.

typedef struct __ILT_ENTRY_64 {
    union {
        DWORD ORDINAL : 16;
        DWORD HINT_NAME_TABE : 32;
    } FIELD_2;
    DWORD ORDINAL_NAME_FLAG : 1;
} ILT_ENTRY_64, * PILT_ENTRY_64;

The structure will hold a 64-bit value and will return the appropriate piece of information (using bit fields) when the member corresponding to that piece of information is accessed.

BASE_RELOC_ENTRY

A structure to represent a base relocation entry during processing.

typedef struct __BASE_RELOC_ENTRY {
    WORD OFFSET : 12;
    WORD TYPE : 4;
} BASE_RELOC_ENTRY, * PBASE_RELOC_ENTRY;
  • OFFSET: Relocation offset.
  • TYPE: Relocation type.

PEFILE

Our parser will represent a PE file as an object type of either PE32FILE or PE64FILE.
These 2 classes only differ in some member definitions but their functionality is identical.
Throughout this post we will use the code from PE64FILE.

Definition

The class is defined as follows:

class PE64FILE
{
public:
    PE64FILE(char* _NAME, FILE* Ppefile);
	
    void PrintInfo();

private:
    char* NAME;
    FILE* Ppefile;
    int _import_directory_count, _import_directory_size;
    int _basreloc_directory_count;

    // HEADERS
    ___IMAGE_DOS_HEADER     PEFILE_DOS_HEADER;
    ___IMAGE_NT_HEADERS64   PEFILE_NT_HEADERS;

    // DOS HEADER
    DWORD PEFILE_DOS_HEADER_EMAGIC;
    LONG  PEFILE_DOS_HEADER_LFANEW;

    // RICH HEADER
    RICH_HEADER_INFO PEFILE_RICH_HEADER_INFO;
    RICH_HEADER PEFILE_RICH_HEADER;

    // NT_HEADERS.Signature
    DWORD PEFILE_NT_HEADERS_SIGNATURE;

    // NT_HEADERS.FileHeader
    WORD PEFILE_NT_HEADERS_FILE_HEADER_MACHINE;
    WORD PEFILE_NT_HEADERS_FILE_HEADER_NUMBER0F_SECTIONS;
    WORD PEFILE_NT_HEADERS_FILE_HEADER_SIZEOF_OPTIONAL_HEADER;

    // NT_HEADERS.OptionalHeader
    DWORD PEFILE_NT_HEADERS_OPTIONAL_HEADER_MAGIC;
    DWORD PEFILE_NT_HEADERS_OPTIONAL_HEADER_SIZEOF_CODE;
    DWORD PEFILE_NT_HEADERS_OPTIONAL_HEADER_SIZEOF_INITIALIZED_DATA;
    DWORD PEFILE_NT_HEADERS_OPTIONAL_HEADER_SIZEOF_UNINITIALIZED_DATA;
    DWORD PEFILE_NT_HEADERS_OPTIONAL_HEADER_ADDRESSOF_ENTRYPOINT;
    DWORD PEFILE_NT_HEADERS_OPTIONAL_HEADER_BASEOF_CODE;
    ULONGLONG PEFILE_NT_HEADERS_OPTIONAL_HEADER_IMAGEBASE;
    DWORD PEFILE_NT_HEADERS_OPTIONAL_HEADER_SECTION_ALIGNMENT;
    DWORD PEFILE_NT_HEADERS_OPTIONAL_HEADER_FILE_ALIGNMENT;
    DWORD PEFILE_NT_HEADERS_OPTIONAL_HEADER_SIZEOF_IMAGE;
    DWORD PEFILE_NT_HEADERS_OPTIONAL_HEADER_SIZEOF_HEADERS;

    ___IMAGE_DATA_DIRECTORY PEFILE_EXPORT_DIRECTORY;
    ___IMAGE_DATA_DIRECTORY PEFILE_IMPORT_DIRECTORY;
    ___IMAGE_DATA_DIRECTORY PEFILE_RESOURCE_DIRECTORY;
    ___IMAGE_DATA_DIRECTORY PEFILE_EXCEPTION_DIRECTORY;
    ___IMAGE_DATA_DIRECTORY PEFILE_SECURITY_DIRECTORY;
    ___IMAGE_DATA_DIRECTORY PEFILE_BASERELOC_DIRECTORY;
    ___IMAGE_DATA_DIRECTORY PEFILE_DEBUG_DIRECTORY;
    ___IMAGE_DATA_DIRECTORY PEFILE_ARCHITECTURE_DIRECTORY;
    ___IMAGE_DATA_DIRECTORY PEFILE_GLOBALPTR_DIRECTORY;
    ___IMAGE_DATA_DIRECTORY PEFILE_TLS_DIRECTORY;
    ___IMAGE_DATA_DIRECTORY PEFILE_LOAD_CONFIG_DIRECTORY;
    ___IMAGE_DATA_DIRECTORY PEFILE_BOUND_IMPORT_DIRECTORY;
    ___IMAGE_DATA_DIRECTORY PEFILE_IAT_DIRECTORY;
    ___IMAGE_DATA_DIRECTORY PEFILE_DELAY_IMPORT_DIRECTORY;
    ___IMAGE_DATA_DIRECTORY PEFILE_COM_DESCRIPTOR_DIRECTORY;

    // SECTION HEADERS
    ___PIMAGE_SECTION_HEADER PEFILE_SECTION_HEADERS;

    // IMPORT TABLE
    ___PIMAGE_IMPORT_DESCRIPTOR PEFILE_IMPORT_TABLE;
    
    // BASE RELOCATION TABLE
    ___PIMAGE_BASE_RELOCATION PEFILE_BASERELOC_TABLE;

    // FUNCTIONS
    
    // ADDRESS RESOLVERS
    int  locate(DWORD VA);
    DWORD resolve(DWORD VA, int index);

    // PARSERS
    void ParseFile();
    void ParseDOSHeader();
    void ParseNTHeaders();
    void ParseSectionHeaders();
    void ParseImportDirectory();
    void ParseBaseReloc();
    void ParseRichHeader();

    // PRINT INFO
    void PrintFileInfo();
    void PrintDOSHeaderInfo();
    void PrintRichHeaderInfo();
    void PrintNTHeadersInfo();
    void PrintSectionHeadersInfo();
    void PrintImportTableInfo();
    void PrintBaseRelocationsInfo();
};

The only public member beside the class constructor is a function called printInfo() which will print information about the file.

The class constructor takes two parameters, a char array representing the name of the file and a file pointer to the actual data of the file.

After that comes a long series of variables definitions, these class members are going to be used internally during the parsing process and we’ll mention each one of them later.

In the end is a series of methods definitions, first two methods are called locate and resolve, I will talk about them in a minute.
The rest are functions responsible for parsing different parts of the file, and functions responsible for printing information about the same parts.

Constructor

The constructor of the class simply sets the file pointer and name variables, then it calls the ParseFile() function.

PE64FILE::PE64FILE(char* _NAME, FILE* _Ppefile) {
	
	NAME = _NAME;
	Ppefile = _Ppefile;

	ParseFile();

}

The ParseFile() function calls the other parser functions:

void PE64FILE::ParseFile() {

	// PARSE DOS HEADER
	ParseDOSHeader();

	// PARSE RICH HEADER
	ParseRichHeader();

	//PARSE NT HEADERS
	ParseNTHeaders();

	// PARSE SECTION HEADERS
	ParseSectionHeaders();

	// PARSE IMPORT DIRECTORY
	ParseImportDirectory();

	// PARSE BASE RELOCATIONS
	ParseBaseReloc();

}

Resolving RVAs

Most of the time, we’ll have a RVA that we’ll need to change to a file offset.
The process of resolving an RVA can be outlined as follows:

  1. Determine which section range contains that RVA:
    • Iterate over all sections and for each section compare the RVA to the section virtual address and to the section virtual address added to the virtual size of the section.
    • If the RVA exists within this range then it belongs to that section.
  2. Calculate the file offset:
    • Subtract the RVA from the section virtual address.
    • Add that value to the raw data pointer of the section.

An example of this is locating a Data Directory.
The IMAGE_DATA_DIRECTORY structure only gives us an RVA of the directory, to locate that directory we’ll need to resolve that address.

I wrote two functions to do this, first one to locate the virtual address (locate()), second one to resolve the address (resolve()).

int PE64FILE::locate(DWORD VA) {
	
	int index;
	
	for (int i = 0; i < PEFILE_NT_HEADERS_FILE_HEADER_NUMBER0F_SECTIONS; i++) {
		if (VA >= PEFILE_SECTION_HEADERS[i].VirtualAddress
			&& VA < (PEFILE_SECTION_HEADERS[i].VirtualAddress + PEFILE_SECTION_HEADERS[i].Misc.VirtualSize)){
			index = i;
			break;
		}
	}
	return index;
}

DWORD PE64FILE::resolve(DWORD VA, int index) {

	return (VA - PEFILE_SECTION_HEADERS[index].VirtualAddress) + PEFILE_SECTION_HEADERS[index].PointerToRawData;

}

locate() iterates over the PEFILE_SECTION_HEADERS array, compares the RVA as described above, then it returns the index of the appropriate section header within the PEFILE_SECTION_HEADERS array.

Please note that in order for these functions to work we’ll need to parse out the section headers and fill the PEFILE_SECTION_HEADERS array first.
We still haven’t discussed this part, but I wanted to talk about the address resolvers first.

main function

The main function of the program is fairly simple, it only does 2 things:

  • Create a file pointer to the given file, and validate that the file was read correctly.
  • Call INITPARSE() on the file, and based on the return value it decides between three actions:
    • Exit.
    • Create a PE32FILE object, call PrintInfo(), close the file pointer then exit.
    • Create a PE64FILE object, call PrintInfo(), close the file pointer then exit.

PrintInfo() calls the other print info functions.

int main(int argc, char* argv[])
{
	if (argc != 2) {
		printf("Usage: %s [path to executable]\n", argv[0]);
		return 1;
	}

	FILE * PpeFile;
	fopen_s(&PpeFile, argv[1], "rb");

	if (PpeFile == NULL) {
		printf("Can't open file.\n");
		return 1;
	}

	if (INITPARSE(PpeFile) == 1) {
		exit(1);
	}
	else if (INITPARSE(PpeFile) == 32) {
		PE32FILE PeFile_1(argv[1], PpeFile);
		PeFile_1.PrintInfo();
		fclose(PpeFile);
		exit(0);
	}
	else if (INITPARSE(PpeFile) == 64) {
		PE64FILE PeFile_1(argv[1], PpeFile);
		PeFile_1.PrintInfo();
		fclose(PpeFile);
		exit(0);
	}

	return 0;
}

INITPARSE()

INITPARSE() is a function defined in PEFILE.cpp.
Its only job is to validate that the given file is a PE file, then determine whether the file is PE32 or PE32+.

It reads the DOS header of the file and checks the DOS MZ header, if not found it returns an error.

After validating the PE file, it sets the file position to (DOS_HEADER.e_lfanew + size of DWORD (PE signature) + size of the file header) which is the exact offset of the beginning of the Optional Header.
Then it reads a WORD, we know that the first WORD of the Optional Header is a magic value that indicates the file type, it then compares that word to IMAGE_NT_OPTIONAL_HDR32_MAGIC and IMAGE_NT_OPTIONAL_HDR64_MAGIC, and based on the comparison results it either returns 32 or 64 indicating PE32 or PE32+, or it returns an error.

int INITPARSE(FILE* PpeFile) {

	___IMAGE_DOS_HEADER TMP_DOS_HEADER;
	WORD PEFILE_TYPE;

	fseek(PpeFile, 0, SEEK_SET);
	fread(&TMP_DOS_HEADER, sizeof(___IMAGE_DOS_HEADER), 1, PpeFile);

	if (TMP_DOS_HEADER.e_magic != ___IMAGE_DOS_SIGNATURE) {
		printf("Error. Not a PE file.\n");
		return 1;
	}

	fseek(PpeFile, (TMP_DOS_HEADER.e_lfanew + sizeof(DWORD) + sizeof(___IMAGE_FILE_HEADER)), SEEK_SET);
	fread(&PEFILE_TYPE, sizeof(WORD), 1, PpeFile);

	if (PEFILE_TYPE == ___IMAGE_NT_OPTIONAL_HDR32_MAGIC) {
		return 32;
	}
	else if (PEFILE_TYPE == ___IMAGE_NT_OPTIONAL_HDR64_MAGIC) {
		return 64;
	}
	else {
		printf("Error while parsing IMAGE_OPTIONAL_HEADER.Magic. Unknown Type.\n");
		return 1;
	}

}

Parsing DOS Header

ParseDOSHeader()

Parsing out the DOS Header is nothing complicated, we just need to read from the beginning of the file an amount of bytes equal to the size of the DOS Header, then we can assign that data to the pre-defined class member PEFILE_DOS_HEADER.
From there we can access all of the struct members, however we’re only interested in e_magic and e_lfanew.

void PE64FILE::ParseDOSHeader() {
	
	fseek(Ppefile, 0, SEEK_SET);
	fread(&PEFILE_DOS_HEADER, sizeof(___IMAGE_DOS_HEADER), 1, Ppefile);

	PEFILE_DOS_HEADER_EMAGIC = PEFILE_DOS_HEADER.e_magic;
	PEFILE_DOS_HEADER_LFANEW = PEFILE_DOS_HEADER.e_lfanew;

}

PrintDOSHeaderInfo()

This function prints e_magic and e_lfanew values.

void PE64FILE::PrintDOSHeaderInfo() {
	
	printf(" DOS HEADER:\n");
	printf(" -----------\n\n");

	printf(" Magic: 0x%X\n", PEFILE_DOS_HEADER_EMAGIC);
	printf(" File address of new exe header: 0x%X\n", PEFILE_DOS_HEADER_LFANEW);

}

Parsing Rich Header

Process

To parse out the Rich Header we’ll need to go through multiple steps.

We don’t know anything about the Rich Header, we don’t know its size, we don’t know where it’s exactly located, we don’t even know if the file we’re processing contains a Rich Header in the first place.

First of all, we need to locate the Rich Header.
We don’t know the exact location, however we have everything we need to locate it.
We know that if a Rich Header exists, then it has to exist between the DOS Stub and the PE signature or the beginning of the NT Headers.
We also know that any Rich Header ends with a 32-bit value Rich followed by the XOR key.

One might rely on the fixed size of the DOS Header and the DOS Stub, however, the default DOS Stub message can be changed, so that size is not guaranteed to be fixed.
A better approach would be to read from the beginning of the file to the start of the NT Headers, then search through that buffer for the Rich sequence, if found then we’ve successfully located the end of the Rich Header, if not found then most likely the file doesn’t contain a Rich Header.

Once we’ve located the end of the Rich Header, we can read the XOR key, then go backwards starting from the Rich signature and keep XORing 4 bytes at a time until we reach the DanS signature which indicates the beginning of the Rich Header.

After obtaining the position and the size of the Rich Header, we can normally read and process the data.

ParseRichHeader()

This function starts by allocating a buffer on the heap, then it reads e_lfanew size of bytes from the beginning of the file and stores the data in the allocated buffer.

It then goes through a loop where it does a linear search byte by byte. In each iteration it compares the current byte and the byte the follows to 0x52 (R) and 0x69 (i).
When the sequence is found, it stores the index in a variable then the loop breaks.

	char* dataPtr = new char[PEFILE_DOS_HEADER_LFANEW];
	fseek(Ppefile, 0, SEEK_SET);
	fread(dataPtr, PEFILE_DOS_HEADER_LFANEW, 1, Ppefile);

	int index_ = 0;

	for (int i = 0; i <= PEFILE_DOS_HEADER_LFANEW; i++) {
		if (dataPtr[i] == 0x52 && dataPtr[i + 1] == 0x69) {
			index_ = i;
			break;
		}
	}

	if (index_ == 0) {
		printf("Error while parsing Rich Header.");
		PEFILE_RICH_HEADER_INFO.entries = 0;
		return;
	}

After that it reads the XOR key, then goes into the decryption loop where in each iteration it increments RichHeaderSize by 4 until it reaches the DanS sequence.

	char key[4];
	memcpy(key, dataPtr + (index_ + 4), 4);

	int indexpointer = index_ - 4;
	int RichHeaderSize = 0;

	while (true) {
		char tmpchar[4];
		memcpy(tmpchar, dataPtr + indexpointer, 4);

		for (int i = 0; i < 4; i++) {
			tmpchar[i] = tmpchar[i] ^ key[i];
		}

		indexpointer -= 4;
		RichHeaderSize += 4;

		if (tmpchar[1] = 0x61 && tmpchar[0] == 0x44) {
			break;
		}
	}

After obtaining the size and the position, it allocates a new buffer for the Rich Header, reads and decrypts the Rich Header, updates PEFILE_RICH_HEADER_INFO with the appropriate data pointer, size and number of entries, then finally it deallocates the buffer it was using for processing.

	char* RichHeaderPtr = new char[RichHeaderSize];
	memcpy(RichHeaderPtr, dataPtr + (index_ - RichHeaderSize), RichHeaderSize);

	for (int i = 0; i < RichHeaderSize; i += 4) {

		for (int x = 0; x < 4; x++) {
			RichHeaderPtr[i + x] = RichHeaderPtr[i + x] ^ key[x];
		}

	}

	PEFILE_RICH_HEADER_INFO.size = RichHeaderSize;
	PEFILE_RICH_HEADER_INFO.ptrToBuffer = RichHeaderPtr;
	PEFILE_RICH_HEADER_INFO.entries = (RichHeaderSize - 16) / 8;

	delete[] dataPtr;

The rest of the function reads each entry of the Rich Header and updates PEFILE_RICH_HEADER.

	PEFILE_RICH_HEADER.entries = new RICH_HEADER_ENTRY[PEFILE_RICH_HEADER_INFO.entries];

	for (int i = 16; i < RichHeaderSize; i += 8) {
		WORD PRODID = (uint16_t)((unsigned char)RichHeaderPtr[i + 3] << 8) | (unsigned char)RichHeaderPtr[i + 2];
		WORD BUILDID = (uint16_t)((unsigned char)RichHeaderPtr[i + 1] << 8) | (unsigned char)RichHeaderPtr[i];
		DWORD USECOUNT = (uint32_t)((unsigned char)RichHeaderPtr[i + 7] << 24) | (unsigned char)RichHeaderPtr[i + 6] << 16 | (unsigned char)RichHeaderPtr[i + 5] << 8 | (unsigned char)RichHeaderPtr[i + 4];
		PEFILE_RICH_HEADER.entries[(i / 8) - 2] = {
			PRODID,
			BUILDID,
			USECOUNT
		};

		if (i + 8 >= RichHeaderSize) {
			PEFILE_RICH_HEADER.entries[(i / 8) - 1] = { 0x0000, 0x0000, 0x00000000 };
		}

	}

	delete[] PEFILE_RICH_HEADER_INFO.ptrToBuffer;

Here’s the full function:

void PE64FILE::ParseRichHeader() {
	
	char* dataPtr = new char[PEFILE_DOS_HEADER_LFANEW];
	fseek(Ppefile, 0, SEEK_SET);
	fread(dataPtr, PEFILE_DOS_HEADER_LFANEW, 1, Ppefile);

	int index_ = 0;

	for (int i = 0; i <= PEFILE_DOS_HEADER_LFANEW; i++) {
		if (dataPtr[i] == 0x52 && dataPtr[i + 1] == 0x69) {
			index_ = i;
			break;
		}
	}

	if (index_ == 0) {
		printf("Error while parsing Rich Header.");
		PEFILE_RICH_HEADER_INFO.entries = 0;
		return;
	}

	char key[4];
	memcpy(key, dataPtr + (index_ + 4), 4);

	int indexpointer = index_ - 4;
	int RichHeaderSize = 0;

	while (true) {
		char tmpchar[4];
		memcpy(tmpchar, dataPtr + indexpointer, 4);

		for (int i = 0; i < 4; i++) {
			tmpchar[i] = tmpchar[i] ^ key[i];
		}

		indexpointer -= 4;
		RichHeaderSize += 4;

		if (tmpchar[1] = 0x61 && tmpchar[0] == 0x44) {
			break;
		}
	}

	char* RichHeaderPtr = new char[RichHeaderSize];
	memcpy(RichHeaderPtr, dataPtr + (index_ - RichHeaderSize), RichHeaderSize);

	for (int i = 0; i < RichHeaderSize; i += 4) {

		for (int x = 0; x < 4; x++) {
			RichHeaderPtr[i + x] = RichHeaderPtr[i + x] ^ key[x];
		}

	}

	PEFILE_RICH_HEADER_INFO.size = RichHeaderSize;
	PEFILE_RICH_HEADER_INFO.ptrToBuffer = RichHeaderPtr;
	PEFILE_RICH_HEADER_INFO.entries = (RichHeaderSize - 16) / 8;

	delete[] dataPtr;

	PEFILE_RICH_HEADER.entries = new RICH_HEADER_ENTRY[PEFILE_RICH_HEADER_INFO.entries];

	for (int i = 16; i < RichHeaderSize; i += 8) {
		WORD PRODID = (uint16_t)((unsigned char)RichHeaderPtr[i + 3] << 8) | (unsigned char)RichHeaderPtr[i + 2];
		WORD BUILDID = (uint16_t)((unsigned char)RichHeaderPtr[i + 1] << 8) | (unsigned char)RichHeaderPtr[i];
		DWORD USECOUNT = (uint32_t)((unsigned char)RichHeaderPtr[i + 7] << 24) | (unsigned char)RichHeaderPtr[i + 6] << 16 | (unsigned char)RichHeaderPtr[i + 5] << 8 | (unsigned char)RichHeaderPtr[i + 4];
		PEFILE_RICH_HEADER.entries[(i / 8) - 2] = {
			PRODID,
			BUILDID,
			USECOUNT
		};

		if (i + 8 >= RichHeaderSize) {
			PEFILE_RICH_HEADER.entries[(i / 8) - 1] = { 0x0000, 0x0000, 0x00000000 };
		}

	}

	delete[] PEFILE_RICH_HEADER_INFO.ptrToBuffer;

}

PrintRichHeaderInfo()

This function iterates over each entry in PEFILE_RICH_HEADER and prints its value.

void PE64FILE::PrintRichHeaderInfo() {
	
	printf(" RICH HEADER:\n");
	printf(" ------------\n\n");

	for (int i = 0; i < PEFILE_RICH_HEADER_INFO.entries; i++) {
		printf(" 0x%X 0x%X 0x%X: %d.%d.%d\n",
			PEFILE_RICH_HEADER.entries[i].buildID,
			PEFILE_RICH_HEADER.entries[i].prodID,
			PEFILE_RICH_HEADER.entries[i].useCount,
			PEFILE_RICH_HEADER.entries[i].buildID,
			PEFILE_RICH_HEADER.entries[i].prodID,
			PEFILE_RICH_HEADER.entries[i].useCount);
	}

}

Parsing NT Headers

ParseNTHeaders()

Similar to the DOS Header, all we need to do is to read from e_lfanew an amount of bytes equal to the size of IMAGE_NT_HEADERS.

After that we can parse out the contents of the File Header and the Optional Header.

The Optional Header contains an array of IMAGE_DATA_DIRECTORY structures which we care about.
To parse out this information, we can use the IMAGE_DIRECTORY_[...] constants defined in winnt.h as array indexes to access the corresponding IMAGE_DATA_DIRECTORY structure of each Data Directory.

void PE64FILE::ParseNTHeaders() {
	
	fseek(Ppefile, PEFILE_DOS_HEADER.e_lfanew, SEEK_SET);
	fread(&PEFILE_NT_HEADERS, sizeof(PEFILE_NT_HEADERS), 1, Ppefile);

	PEFILE_NT_HEADERS_SIGNATURE = PEFILE_NT_HEADERS.Signature;

	PEFILE_NT_HEADERS_FILE_HEADER_MACHINE = PEFILE_NT_HEADERS.FileHeader.Machine;
	PEFILE_NT_HEADERS_FILE_HEADER_NUMBER0F_SECTIONS = PEFILE_NT_HEADERS.FileHeader.NumberOfSections;
	PEFILE_NT_HEADERS_FILE_HEADER_SIZEOF_OPTIONAL_HEADER = PEFILE_NT_HEADERS.FileHeader.SizeOfOptionalHeader;

	PEFILE_NT_HEADERS_OPTIONAL_HEADER_MAGIC = PEFILE_NT_HEADERS.OptionalHeader.Magic;
	PEFILE_NT_HEADERS_OPTIONAL_HEADER_SIZEOF_CODE = PEFILE_NT_HEADERS.OptionalHeader.SizeOfCode;
	PEFILE_NT_HEADERS_OPTIONAL_HEADER_SIZEOF_INITIALIZED_DATA = PEFILE_NT_HEADERS.OptionalHeader.SizeOfInitializedData;
	PEFILE_NT_HEADERS_OPTIONAL_HEADER_SIZEOF_UNINITIALIZED_DATA = PEFILE_NT_HEADERS.OptionalHeader.SizeOfUninitializedData;
	PEFILE_NT_HEADERS_OPTIONAL_HEADER_ADDRESSOF_ENTRYPOINT = PEFILE_NT_HEADERS.OptionalHeader.AddressOfEntryPoint;
	PEFILE_NT_HEADERS_OPTIONAL_HEADER_BASEOF_CODE = PEFILE_NT_HEADERS.OptionalHeader.BaseOfCode;
	PEFILE_NT_HEADERS_OPTIONAL_HEADER_IMAGEBASE = PEFILE_NT_HEADERS.OptionalHeader.ImageBase;
	PEFILE_NT_HEADERS_OPTIONAL_HEADER_SECTION_ALIGNMENT = PEFILE_NT_HEADERS.OptionalHeader.SectionAlignment;
	PEFILE_NT_HEADERS_OPTIONAL_HEADER_FILE_ALIGNMENT = PEFILE_NT_HEADERS.OptionalHeader.FileAlignment;
	PEFILE_NT_HEADERS_OPTIONAL_HEADER_SIZEOF_IMAGE = PEFILE_NT_HEADERS.OptionalHeader.SizeOfImage;
	PEFILE_NT_HEADERS_OPTIONAL_HEADER_SIZEOF_HEADERS = PEFILE_NT_HEADERS.OptionalHeader.SizeOfHeaders;

	PEFILE_EXPORT_DIRECTORY = PEFILE_NT_HEADERS.OptionalHeader.DataDirectory[___IMAGE_DIRECTORY_ENTRY_EXPORT];
	PEFILE_IMPORT_DIRECTORY = PEFILE_NT_HEADERS.OptionalHeader.DataDirectory[___IMAGE_DIRECTORY_ENTRY_IMPORT];
	PEFILE_RESOURCE_DIRECTORY = PEFILE_NT_HEADERS.OptionalHeader.DataDirectory[___IMAGE_DIRECTORY_ENTRY_RESOURCE];
	PEFILE_EXCEPTION_DIRECTORY = PEFILE_NT_HEADERS.OptionalHeader.DataDirectory[___IMAGE_DIRECTORY_ENTRY_EXCEPTION];
	PEFILE_SECURITY_DIRECTORY = PEFILE_NT_HEADERS.OptionalHeader.DataDirectory[___IMAGE_DIRECTORY_ENTRY_SECURITY];
	PEFILE_BASERELOC_DIRECTORY = PEFILE_NT_HEADERS.OptionalHeader.DataDirectory[___IMAGE_DIRECTORY_ENTRY_BASERELOC];
	PEFILE_DEBUG_DIRECTORY = PEFILE_NT_HEADERS.OptionalHeader.DataDirectory[___IMAGE_DIRECTORY_ENTRY_DEBUG];
	PEFILE_ARCHITECTURE_DIRECTORY = PEFILE_NT_HEADERS.OptionalHeader.DataDirectory[___IMAGE_DIRECTORY_ENTRY_ARCHITECTURE];
	PEFILE_GLOBALPTR_DIRECTORY = PEFILE_NT_HEADERS.OptionalHeader.DataDirectory[___IMAGE_DIRECTORY_ENTRY_GLOBALPTR];
	PEFILE_TLS_DIRECTORY = PEFILE_NT_HEADERS.OptionalHeader.DataDirectory[___IMAGE_DIRECTORY_ENTRY_TLS];
	PEFILE_LOAD_CONFIG_DIRECTORY = PEFILE_NT_HEADERS.OptionalHeader.DataDirectory[___IMAGE_DIRECTORY_ENTRY_LOAD_CONFIG];
	PEFILE_BOUND_IMPORT_DIRECTORY = PEFILE_NT_HEADERS.OptionalHeader.DataDirectory[___IMAGE_DIRECTORY_ENTRY_BOUND_IMPORT];
	PEFILE_IAT_DIRECTORY = PEFILE_NT_HEADERS.OptionalHeader.DataDirectory[___IMAGE_DIRECTORY_ENTRY_IAT];
	PEFILE_DELAY_IMPORT_DIRECTORY = PEFILE_NT_HEADERS.OptionalHeader.DataDirectory[___IMAGE_DIRECTORY_ENTRY_DELAY_IMPORT];
	PEFILE_COM_DESCRIPTOR_DIRECTORY = PEFILE_NT_HEADERS.OptionalHeader.DataDirectory[___IMAGE_DIRECTORY_ENTRY_COM_DESCRIPTOR];

}

PrintNTHeadersInfo()

This function prints the data obtained from the File Header and the Optional Header, and for each Data Directory it prints its RVA and size.

void PE64FILE::PrintNTHeadersInfo() {
	
	printf(" NT HEADERS:\n");
	printf(" -----------\n\n");

	printf(" PE Signature: 0x%X\n", PEFILE_NT_HEADERS_SIGNATURE);

	printf("\n File Header:\n\n");
	printf("   Machine: 0x%X\n", PEFILE_NT_HEADERS_FILE_HEADER_MACHINE);
	printf("   Number of sections: 0x%X\n", PEFILE_NT_HEADERS_FILE_HEADER_NUMBER0F_SECTIONS);
	printf("   Size of optional header: 0x%X\n", PEFILE_NT_HEADERS_FILE_HEADER_SIZEOF_OPTIONAL_HEADER);

	printf("\n Optional Header:\n\n");
	printf("   Magic: 0x%X\n", PEFILE_NT_HEADERS_OPTIONAL_HEADER_MAGIC);
	printf("   Size of code section: 0x%X\n", PEFILE_NT_HEADERS_OPTIONAL_HEADER_SIZEOF_CODE);
	printf("   Size of initialized data: 0x%X\n", PEFILE_NT_HEADERS_OPTIONAL_HEADER_SIZEOF_INITIALIZED_DATA);
	printf("   Size of uninitialized data: 0x%X\n", PEFILE_NT_HEADERS_OPTIONAL_HEADER_SIZEOF_UNINITIALIZED_DATA);
	printf("   Address of entry point: 0x%X\n", PEFILE_NT_HEADERS_OPTIONAL_HEADER_ADDRESSOF_ENTRYPOINT);
	printf("   RVA of start of code section: 0x%X\n", PEFILE_NT_HEADERS_OPTIONAL_HEADER_BASEOF_CODE);
	printf("   Desired image base: 0x%X\n", PEFILE_NT_HEADERS_OPTIONAL_HEADER_IMAGEBASE);
	printf("   Section alignment: 0x%X\n", PEFILE_NT_HEADERS_OPTIONAL_HEADER_SECTION_ALIGNMENT);
	printf("   File alignment: 0x%X\n", PEFILE_NT_HEADERS_OPTIONAL_HEADER_FILE_ALIGNMENT);
	printf("   Size of image: 0x%X\n", PEFILE_NT_HEADERS_OPTIONAL_HEADER_SIZEOF_IMAGE);
	printf("   Size of headers: 0x%X\n", PEFILE_NT_HEADERS_OPTIONAL_HEADER_SIZEOF_HEADERS);

	printf("\n Data Directories:\n");
	printf("\n   * Export Directory:\n");
	printf("       RVA: 0x%X\n", PEFILE_EXPORT_DIRECTORY.VirtualAddress);
	printf("       Size: 0x%X\n", PEFILE_EXPORT_DIRECTORY.Size);
	.
	.
	[REDACTED]
	.
	.
	printf("\n   * COM Runtime Descriptor:\n");
	printf("       RVA: 0x%X\n", PEFILE_COM_DESCRIPTOR_DIRECTORY.VirtualAddress);
	printf("       Size: 0x%X\n", PEFILE_COM_DESCRIPTOR_DIRECTORY.Size);

}

Parsing Section Headers

ParseSectionHeaders()

This function starts by assigning the PEFILE_SECTION_HEADERS class member to a pointer to an IMAGE_SECTION_HEADER array of the count of PEFILE_NT_HEADERS_FILE_HEADER_NUMBEROF_SECTIONS.

Then it goes into a loop of PEFILE_NT_HEADERS_FILE_HEADER_NUMBEROF_SECTIONS iterations where in each iteration it changes the file offset to (e_lfanew + size of NT Headers + loop counter multiplied by the size of a section header) to reach the beginning of the next Section Header, then it reads the new Section Header and assigns it to the next element of PEFILE_SECTION_HEADERS.

void PE64FILE::ParseSectionHeaders() {
	
	PEFILE_SECTION_HEADERS = new ___IMAGE_SECTION_HEADER[PEFILE_NT_HEADERS_FILE_HEADER_NUMBER0F_SECTIONS];
	for (int i = 0; i < PEFILE_NT_HEADERS_FILE_HEADER_NUMBER0F_SECTIONS; i++) {
		int offset = (PEFILE_DOS_HEADER.e_lfanew + sizeof(PEFILE_NT_HEADERS)) + (i * ___IMAGE_SIZEOF_SECTION_HEADER);
		fseek(Ppefile, offset, SEEK_SET);
		fread(&PEFILE_SECTION_HEADERS[i], ___IMAGE_SIZEOF_SECTION_HEADER, 1, Ppefile);
	}

}

PrintSectionHeadersInfo()

This function loops over the Section Headers array (filled by ParseSectionHeaders()), and it prints information about each section.

void PE64FILE::PrintSectionHeadersInfo() {
	
	printf(" SECTION HEADERS:\n");
	printf(" ----------------\n\n");

	for (int i = 0; i < PEFILE_NT_HEADERS_FILE_HEADER_NUMBER0F_SECTIONS; i++) {
		printf("   * %.8s:\n", PEFILE_SECTION_HEADERS[i].Name);
		printf("        VirtualAddress: 0x%X\n", PEFILE_SECTION_HEADERS[i].VirtualAddress);
		printf("        VirtualSize: 0x%X\n", PEFILE_SECTION_HEADERS[i].Misc.VirtualSize);
		printf("        PointerToRawData: 0x%X\n", PEFILE_SECTION_HEADERS[i].PointerToRawData);
		printf("        SizeOfRawData: 0x%X\n", PEFILE_SECTION_HEADERS[i].SizeOfRawData);
		printf("        Characteristics: 0x%X\n\n", PEFILE_SECTION_HEADERS[i].Characteristics);
	}

}

Parsing Imports

ParseImportDirectory()

To parse out the Import Directory Table we need to determine the count of IMAGE_IMPORT_DESCRIPTORs first.

This function starts by resolving the file offset of the Import Directory, then it goes into a loop where in each loop it keeps reading the next import descriptor.
In each iteration it checks if the descriptor has zeroed out values, if that is the case then we’ve reached the end of the Import Directory, so it breaks.
Otherwise it increments _import_directory_count and the loop continues.

After finding the size of the Import Directory, the function assigns the PEFILE_IMPORT_TABLE class member to a pointer to an IMAGE_IMPORT_DESCRIPTOR array of the count of _import_directory_count then goes into another loop similar to the one we’ve seen in ParseSectionHeaders() to parse out the import descriptors.

void PE64FILE::ParseImportDirectory() {
	
	DWORD _import_directory_address = resolve(PEFILE_IMPORT_DIRECTORY.VirtualAddress, locate(PEFILE_IMPORT_DIRECTORY.VirtualAddress));
	_import_directory_count = 0;

	while (true) {
		___IMAGE_IMPORT_DESCRIPTOR tmp;
		int offset = (_import_directory_count * sizeof(___IMAGE_IMPORT_DESCRIPTOR)) + _import_directory_address;
		fseek(Ppefile, offset, SEEK_SET);
		fread(&tmp, sizeof(___IMAGE_IMPORT_DESCRIPTOR), 1, Ppefile);

		if (tmp.Name == 0x00000000 && tmp.FirstThunk == 0x00000000) {
			_import_directory_count -= 1;
			_import_directory_size = _import_directory_count * sizeof(___IMAGE_IMPORT_DESCRIPTOR);
			break;
		}

		_import_directory_count++;
	}

	PEFILE_IMPORT_TABLE = new ___IMAGE_IMPORT_DESCRIPTOR[_import_directory_count];

	for (int i = 0; i < _import_directory_count; i++) {
		int offset = (i * sizeof(___IMAGE_IMPORT_DESCRIPTOR)) + _import_directory_address;
		fseek(Ppefile, offset, SEEK_SET);
		fread(&PEFILE_IMPORT_TABLE[i], sizeof(___IMAGE_IMPORT_DESCRIPTOR), 1, Ppefile);
	}

}

PrintImportTableInfo()

After obtaining the import descriptors, further parsing is needed to retrieve information about the imported functions.
This is done by the PrintImportTableInfo() function.

This function iterates over the import descriptors, and for each descriptor it resolves the file offset of the DLL name, retrieves the DLL name then prints it, it also prints the ILT RVA, the IAT RVA and whether the import is bound or not.

After that it resolves the file offset of the ILT then it parses out each ILT entry.
If the Ordinal/Name flag is set it prints the function ordinal, otherwise it prints the function name, the hint RVA and the hint.

If the ILT entry is zeroed out, the loop breaks and the next import descriptor parsing iteration starts.

We’ve discussed the details about this in the PE imports post.

void PE64FILE::PrintImportTableInfo() {
	
	printf(" IMPORT TABLE:\n");
	printf(" ----------------\n\n");

	for (int i = 0; i < _import_directory_count; i++) {
		DWORD NameAddr = resolve(PEFILE_IMPORT_TABLE[i].Name, locate(PEFILE_IMPORT_TABLE[i].Name));
		int NameSize = 0;

		while (true) {
			char tmp;
			fseek(Ppefile, (NameAddr + NameSize), SEEK_SET);
			fread(&tmp, sizeof(char), 1, Ppefile);

			if (tmp == 0x00) {
				break;
			}

			NameSize++;
		}

		char* Name = new char[NameSize + 2];
		fseek(Ppefile, NameAddr, SEEK_SET);
		fread(Name, (NameSize * sizeof(char)) + 1, 1, Ppefile);
		printf("   * %s:\n", Name);
		delete[] Name;

		printf("       ILT RVA: 0x%X\n", PEFILE_IMPORT_TABLE[i].DUMMYUNIONNAME.OriginalFirstThunk);
		printf("       IAT RVA: 0x%X\n", PEFILE_IMPORT_TABLE[i].FirstThunk);

		if (PEFILE_IMPORT_TABLE[i].TimeDateStamp == 0) {
			printf("       Bound: FALSE\n");
		}
		else if (PEFILE_IMPORT_TABLE[i].TimeDateStamp == -1) {
			printf("       Bound: TRUE\n");
		}

		printf("\n");

		DWORD ILTAddr = resolve(PEFILE_IMPORT_TABLE[i].DUMMYUNIONNAME.OriginalFirstThunk, locate(PEFILE_IMPORT_TABLE[i].DUMMYUNIONNAME.OriginalFirstThunk));
		int entrycounter = 0;

		while (true) {

			ILT_ENTRY_64 entry;

			fseek(Ppefile, (ILTAddr + (entrycounter * sizeof(QWORD))), SEEK_SET);
			fread(&entry, sizeof(ILT_ENTRY_64), 1, Ppefile);

			BYTE flag = entry.ORDINAL_NAME_FLAG;
			DWORD HintRVA = 0x0;
			WORD ordinal = 0x0;

			if (flag == 0x0) {
				HintRVA = entry.FIELD_2.HINT_NAME_TABE;
			}
			else if (flag == 0x01) {
				ordinal = entry.FIELD_2.ORDINAL;
			}

			if (flag == 0x0 && HintRVA == 0x0 && ordinal == 0x0) {
				break;
			}

			printf("\n       Entry:\n");

			if (flag == 0x0) {
				___IMAGE_IMPORT_BY_NAME hint;

				DWORD HintAddr = resolve(HintRVA, locate(HintRVA));
				fseek(Ppefile, HintAddr, SEEK_SET);
				fread(&hint, sizeof(___IMAGE_IMPORT_BY_NAME), 1, Ppefile);
				printf("         Name: %s\n", hint.Name);
				printf("         Hint RVA: 0x%X\n", HintRVA);
				printf("         Hint: 0x%X\n", hint.Hint);
			}
			else if (flag == 1) {
				printf("         Ordinal: 0x%X\n", ordinal);
			}

			entrycounter++;
		}

		printf("\n   ----------------------\n\n");

	}

}

Parsing Base Relocations

ParseBaseReloc()

This function follows the same process we’ve seen in ParseImportDirectory().
It resolves the file offset of the Base Relocation Directory, then it loops over each relocation block until it reaches a zeroed out block. Then it parses out these blocks and saves each IMAGE_BASE_RELOCATION structure in PEFILE_BASERELOC_TABLE.
One thing to note here that is different from what we’ve seen in ParseImportDirectory() is that in addition to keeping a block counter we also keep a size counter that’s incremented by adding the value of SizeOfBlock of each block in each iteration.
We do this because relocation blocks don’t have a fixed size, and in order to correctly calculate the offset of the next relocation block we need the total size of the previous blocks.

void PE64FILE::ParseBaseReloc() {
	
	DWORD _basereloc_directory_address = resolve(PEFILE_BASERELOC_DIRECTORY.VirtualAddress, locate(PEFILE_BASERELOC_DIRECTORY.VirtualAddress));
	_basreloc_directory_count = 0;
	int _basereloc_size_counter = 0;

	while (true) {
		___IMAGE_BASE_RELOCATION tmp;

		int offset = (_basereloc_size_counter + _basereloc_directory_address);

		fseek(Ppefile, offset, SEEK_SET);
		fread(&tmp, sizeof(___IMAGE_BASE_RELOCATION), 1, Ppefile);

		if (tmp.VirtualAddress == 0x00000000 &&
			tmp.SizeOfBlock == 0x00000000) {
			break;
		}

		_basreloc_directory_count++;
		_basereloc_size_counter += tmp.SizeOfBlock;
	}

	PEFILE_BASERELOC_TABLE = new ___IMAGE_BASE_RELOCATION[_basreloc_directory_count];

	_basereloc_size_counter = 0;

	for (int i = 0; i < _basreloc_directory_count; i++) {
		int offset = _basereloc_directory_address + _basereloc_size_counter;
		fseek(Ppefile, offset, SEEK_SET);
		fread(&PEFILE_BASERELOC_TABLE[i], sizeof(___IMAGE_BASE_RELOCATION), 1, Ppefile);
		_basereloc_size_counter += PEFILE_BASERELOC_TABLE[i].SizeOfBlock;
	}

}

PrintBaseRelocationInfo()

This function iterates over the base relocation blocks, and for each block it resolves the file offset of the block, then it prints the block RVA, size and number of entries (calculated by subtracting the size of IMAGE_BASE_RELOCATION from the block size then dividing that by the size of a WORD).
After that it iterates over the relocation entries and prints the relocation value, and from that value it separates the type and the offset and prints each one of them.

We’ve discussed the details about this in the PE base relocations post.

void PE64FILE::PrintBaseRelocationsInfo() {
	
	printf(" BASE RELOCATIONS TABLE:\n");
	printf(" -----------------------\n");

	int szCounter = sizeof(___IMAGE_BASE_RELOCATION);

	for (int i = 0; i < _basreloc_directory_count; i++) {

		DWORD PAGERVA, BLOCKSIZE, BASE_RELOC_ADDR;
		int ENTRIES;

		BASE_RELOC_ADDR = resolve(PEFILE_BASERELOC_DIRECTORY.VirtualAddress, locate(PEFILE_BASERELOC_DIRECTORY.VirtualAddress));
		PAGERVA = PEFILE_BASERELOC_TABLE[i].VirtualAddress;
		BLOCKSIZE = PEFILE_BASERELOC_TABLE[i].SizeOfBlock;
		ENTRIES = (BLOCKSIZE - sizeof(___IMAGE_BASE_RELOCATION)) / sizeof(WORD);

		printf("\n   Block 0x%X: \n", i);
		printf("     Page RVA: 0x%X\n", PAGERVA);
		printf("     Block size: 0x%X\n", BLOCKSIZE);
		printf("     Number of entries: 0x%X\n", ENTRIES);
		printf("\n     Entries:\n");

		for (int i = 0; i < ENTRIES; i++) {

			BASE_RELOC_ENTRY entry;

			int offset = (BASE_RELOC_ADDR + szCounter + (i * sizeof(WORD)));

			fseek(Ppefile, offset, SEEK_SET);
			fread(&entry, sizeof(WORD), 1, Ppefile);

			printf("\n       * Value: 0x%X\n", entry);
			printf("         Relocation Type: 0x%X\n", entry.TYPE);
			printf("         Offset: 0x%X\n", entry.OFFSET);

		}
		printf("\n   ----------------------\n\n");
		szCounter += BLOCKSIZE;
	}

}

Conclusion

Here’s the full output after running the parser on a file:

Desktop>.\PE-Parser.exe .\SimpleApp64.exe


 FILE: .\SimpleApp64.exe
 TYPE: 0x20B (PE32+)

 ----------------------------------

 DOS HEADER:
 -----------

 Magic: 0x5A4D
 File address of new exe header: 0x100

 ----------------------------------

 RICH HEADER:
 ------------

 0x7809 0x93 0xA: 30729.147.10
 0x6FCB 0x101 0x2: 28619.257.2
 0x6FCB 0x105 0x11: 28619.261.17
 0x6FCB 0x104 0xA: 28619.260.10
 0x6FCB 0x103 0x3: 28619.259.3
 0x685B 0x101 0x5: 26715.257.5
 0x0 0x1 0x30: 0.1.48
 0x7086 0x109 0x1: 28806.265.1
 0x7086 0xFF 0x1: 28806.255.1
 0x7086 0x102 0x1: 28806.258.1

 ----------------------------------

 NT HEADERS:
 -----------

 PE Signature: 0x4550

 File Header:

   Machine: 0x8664
   Number of sections: 0x6
   Size of optional header: 0xF0

 Optional Header:

   Magic: 0x20B
   Size of code section: 0xE00
   Size of initialized data: 0x1E00
   Size of uninitialized data: 0x0
   Address of entry point: 0x12C4
   RVA of start of code section: 0x1000
   Desired image base: 0x40000000
   Section alignment: 0x1000
   File alignment: 0x200
   Size of image: 0x7000
   Size of headers: 0x400

 Data Directories:

   * Export Directory:
       RVA: 0x0
       Size: 0x0

   * Import Directory:
       RVA: 0x27AC
       Size: 0xB4

   * Resource Directory:
       RVA: 0x5000
       Size: 0x1E0

   * Exception Directory:
       RVA: 0x4000
       Size: 0x168

   * Security Directory:
       RVA: 0x0
       Size: 0x0

   * Base Relocation Table:
       RVA: 0x6000
       Size: 0x28

   * Debug Directory:
       RVA: 0x2248
       Size: 0x70

   * Architecture Specific Data:
       RVA: 0x0
       Size: 0x0

   * RVA of GlobalPtr:
       RVA: 0x0
       Size: 0x0

   * TLS Directory:
       RVA: 0x0
       Size: 0x0

   * Load Configuration Directory:
       RVA: 0x22C0
       Size: 0x130

   * Bound Import Directory:
       RVA: 0x0
       Size: 0x0

   * Import Address Table:
       RVA: 0x2000
       Size: 0x198

   * Delay Load Import Descriptors:
       RVA: 0x0
       Size: 0x0

   * COM Runtime Descriptor:
       RVA: 0x0
       Size: 0x0

 ----------------------------------

 SECTION HEADERS:
 ----------------

   * .text:
        VirtualAddress: 0x1000
        VirtualSize: 0xD2C
        PointerToRawData: 0x400
        SizeOfRawData: 0xE00
        Characteristics: 0x60000020

   * .rdata:
        VirtualAddress: 0x2000
        VirtualSize: 0xE3C
        PointerToRawData: 0x1200
        SizeOfRawData: 0x1000
        Characteristics: 0x40000040

   * .data:
        VirtualAddress: 0x3000
        VirtualSize: 0x638
        PointerToRawData: 0x2200
        SizeOfRawData: 0x200
        Characteristics: 0xC0000040

   * .pdata:
        VirtualAddress: 0x4000
        VirtualSize: 0x168
        PointerToRawData: 0x2400
        SizeOfRawData: 0x200
        Characteristics: 0x40000040

   * .rsrc:
        VirtualAddress: 0x5000
        VirtualSize: 0x1E0
        PointerToRawData: 0x2600
        SizeOfRawData: 0x200
        Characteristics: 0x40000040

   * .reloc:
        VirtualAddress: 0x6000
        VirtualSize: 0x28
        PointerToRawData: 0x2800
        SizeOfRawData: 0x200
        Characteristics: 0x42000040


 ----------------------------------

 IMPORT TABLE:
 ----------------

   * USER32.dll:
       ILT RVA: 0x28E0
       IAT RVA: 0x2080
       Bound: FALSE


       Entry:
         Name: MessageBoxA
         Hint RVA: 0x29F8
         Hint: 0x283

   ----------------------

   * VCRUNTIME140.dll:
       ILT RVA: 0x28F0
       IAT RVA: 0x2090
       Bound: FALSE


       Entry:
         Name: memset
         Hint RVA: 0x2A5E
         Hint: 0x3E

       Entry:
         Name: __current_exception_context
         Hint RVA: 0x2A40
         Hint: 0x1C

       Entry:
         Name: __current_exception
         Hint RVA: 0x2A2A
         Hint: 0x1B

       Entry:
         Name: __C_specific_handler
         Hint RVA: 0x2A12
         Hint: 0x8

   ----------------------

   * api-ms-win-crt-runtime-l1-1-0.dll:
       ILT RVA: 0x2948
       IAT RVA: 0x20E8
       Bound: FALSE


       Entry:
         Name: _crt_atexit
         Hint RVA: 0x2C12
         Hint: 0x1E

       Entry:
         Name: terminate
         Hint RVA: 0x2C20
         Hint: 0x67

       Entry:
         Name: _exit
         Hint RVA: 0x2B30
         Hint: 0x23

       Entry:
         Name: _register_thread_local_exe_atexit_callback
         Hint RVA: 0x2B76
         Hint: 0x3D

       Entry:
         Name: _c_exit
         Hint RVA: 0x2B6C
         Hint: 0x15

       Entry:
         Name: exit
         Hint RVA: 0x2B28
         Hint: 0x55

       Entry:
         Name: _initterm_e
         Hint RVA: 0x2B1A
         Hint: 0x37

       Entry:
         Name: _initterm
         Hint RVA: 0x2B0E
         Hint: 0x36

       Entry:
         Name: _get_initial_narrow_environment
         Hint RVA: 0x2AEC
         Hint: 0x28

       Entry:
         Name: _initialize_narrow_environment
         Hint RVA: 0x2ACA
         Hint: 0x33

       Entry:
         Name: _configure_narrow_argv
         Hint RVA: 0x2AB0
         Hint: 0x18

       Entry:
         Name: _initialize_onexit_table
         Hint RVA: 0x2BDA
         Hint: 0x34

       Entry:
         Name: _set_app_type
         Hint RVA: 0x2A8C
         Hint: 0x42

       Entry:
         Name: _seh_filter_exe
         Hint RVA: 0x2A7A
         Hint: 0x40

       Entry:
         Name: _cexit
         Hint RVA: 0x2B62
         Hint: 0x16

       Entry:
         Name: __p___argv
         Hint RVA: 0x2B54
         Hint: 0x5

       Entry:
         Name: __p___argc
         Hint RVA: 0x2B46
         Hint: 0x4

       Entry:
         Name: _register_onexit_function
         Hint RVA: 0x2BF6
         Hint: 0x3C

   ----------------------

   * api-ms-win-crt-math-l1-1-0.dll:
       ILT RVA: 0x2938
       IAT RVA: 0x20D8
       Bound: FALSE


       Entry:
         Name: __setusermatherr
         Hint RVA: 0x2A9C
         Hint: 0x9

   ----------------------

   * api-ms-win-crt-stdio-l1-1-0.dll:
       ILT RVA: 0x29E0
       IAT RVA: 0x2180
       Bound: FALSE


       Entry:
         Name: __p__commode
         Hint RVA: 0x2BCA
         Hint: 0x1

       Entry:
         Name: _set_fmode
         Hint RVA: 0x2B38
         Hint: 0x54

   ----------------------

   * api-ms-win-crt-locale-l1-1-0.dll:
       ILT RVA: 0x2928
       IAT RVA: 0x20C8
       Bound: FALSE


       Entry:
         Name: _configthreadlocale
         Hint RVA: 0x2BA4
         Hint: 0x8

   ----------------------

   * api-ms-win-crt-heap-l1-1-0.dll:
       ILT RVA: 0x2918
       IAT RVA: 0x20B8
       Bound: FALSE


       Entry:
         Name: _set_new_mode
         Hint RVA: 0x2BBA
         Hint: 0x16

   ----------------------


 ----------------------------------

 BASE RELOCATIONS TABLE:
 -----------------------

   Block 0x0:
     Page RVA: 0x2000
     Block size: 0x28
     Number of entries: 0x10

     Entries:

       * Value: 0xA198
         Relocation Type: 0xA
         Offset: 0x198

       * Value: 0xA1A0
         Relocation Type: 0xA
         Offset: 0x1A0

       * Value: 0xA1A8
         Relocation Type: 0xA
         Offset: 0x1A8

       * Value: 0xA1B0
         Relocation Type: 0xA
         Offset: 0x1B0

       * Value: 0xA1B8
         Relocation Type: 0xA
         Offset: 0x1B8

       * Value: 0xA1C8
         Relocation Type: 0xA
         Offset: 0x1C8

       * Value: 0xA1E0
         Relocation Type: 0xA
         Offset: 0x1E0

       * Value: 0xA1E8
         Relocation Type: 0xA
         Offset: 0x1E8

       * Value: 0xA220
         Relocation Type: 0xA
         Offset: 0x220

       * Value: 0xA228
         Relocation Type: 0xA
         Offset: 0x228

       * Value: 0xA318
         Relocation Type: 0xA
         Offset: 0x318

       * Value: 0xA330
         Relocation Type: 0xA
         Offset: 0x330

       * Value: 0xA338
         Relocation Type: 0xA
         Offset: 0x338

       * Value: 0xA3D8
         Relocation Type: 0xA
         Offset: 0x3D8

       * Value: 0xA3E0
         Relocation Type: 0xA
         Offset: 0x3E0

       * Value: 0xA3E8
         Relocation Type: 0xA
         Offset: 0x3E8

   ----------------------


 ----------------------------------

I hope that seeing actual code has given you a better understanding of what we’ve discussed throughout the previous posts.
I believe that there are better ways for implementation than the ones I have presented, I’m in no way a c++ programmer and I know that there’s always room for improvement, so feel free to reach out to me, any feedback would be much appreciated.

Thanks for reading.

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