• Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 702
  • Last Modified:

PE header - Reserved Words at IMAGE_DOS_HEADER

In working on some related code, I noticed that kernel32.dll wasn't identical between various processes executing on my system. Naturally, I was curious why - perhaps some spyware that patched kernel32.dll in some processes but not others? I wrote a quick program to compare the memory of kernel32.dll between all processes on my system and found that a few (5 to be exact) had modifications in the PE header. Doesn't appear to be an important difference, but I am curious why five instances of my kernel32.dll are different than the rest - very odd.

In most of my processes, the IMAGE_DOS_HEADER->e_res =
  44 65 74 6F 75 72 73 21 00 00 00 00 00 00 00 .... [zeros] ...

However, in the five 'modified' versions, IMAGE_DOS_HEADER->e_res =
 00 00 00 00 00 00 00 ..... [zeros] ...

Does anyone happen to know what the 'reserved words' are used for in the IMAGE_DOS_HEADER, and why they would be zeroed in five cases?

======================

typedef struct _IMAGE_DOS_HEADER {      // DOS .EXE header
    WORD   e_magic;                     // Magic number
    WORD   e_cblp;                      // Bytes on last page of file
    WORD   e_cp;                        // Pages in file
    WORD   e_crlc;                      // Relocations
    WORD   e_cparhdr;                   // Size of header in paragraphs
    WORD   e_minalloc;                  // Minimum extra paragraphs needed
    WORD   e_maxalloc;                  // Maximum extra paragraphs needed
    WORD   e_ss;                        // Initial (relative) SS value
    WORD   e_sp;                        // Initial SP value
    WORD   e_csum;                      // Checksum
    WORD   e_ip;                        // Initial IP value
    WORD   e_cs;                        // Initial (relative) CS value
    WORD   e_lfarlc;                    // File address of relocation table
    WORD   e_ovno;                      // Overlay number
    WORD   e_res[4];                    // Reserved words
    WORD   e_oemid;                     // OEM identifier (for e_oeminfo)
    WORD   e_oeminfo;                   // OEM information; e_oemid specific
    WORD   e_res2[10];                  // Reserved words
    LONG   e_lfanew;                    // File address of new exe header
  } IMAGE_DOS_HEADER, *PIMAGE_DOS_HEADER;
0
jimstar
Asked:
jimstar
1 Solution
 
jkrCommented:
Look at the ASCII representation of "44 65 74 6F 75 72 73 21" - it reads "Detours": http://research.microsoft.com/sn/detours/
0
 
jimstarAuthor Commented:
Clever - thanks.
0

Featured Post

Concerto Cloud for Software Providers & ISVs

Can Concerto Cloud Services help you focus on evolving your application offerings, while delivering the best cloud experience to your customers? From DevOps to revenue models and customer support, the answer is yes!

Learn how Concerto can help you.

Tackle projects and never again get stuck behind a technical roadblock.
Join Now