Didier Stevens

Sunday 5 July 2015

base64dump.py Version 0.0.1

Filed under: My Software — Didier Stevens @ 14:54

A new tool, a new video:

base64dump_V0_0_1.zip (https)
MD5: 350C12F677E08030E0DD95339AC3604D
SHA256: 1F8156B43C8B52B7E5620B7A8CD19CFB48F42972E8625994603DDA47E07C9B35

Friday 26 June 2015

Update: oledump.py Version 0.0.17 – ExitCode

Filed under: My Software,Update — Didier Stevens @ 9:44

Here is a new version of oledump with a couple of bugfixes and a new feature: ExitCode.

The ExitCode of the Python program running oledump.py is 0, except if the analyzed file contains macros, then it is 1. You can’t use options if you want the ExitCode.

Thanks Philippe for the idea.

oledump_V0_0_17.zip (https)
MD5: 5AF76C638AA300F6703C6913F80C061F
SHA256: A04DDE83621770BCD96D622C7B57C424E109949FD5EE2523987F30A34FD319E1

Tuesday 9 June 2015

pcap-rename.py

Filed under: My Software,Networking — Didier Stevens @ 0:00

pcap-rename.py is a program to rename pcap files with a timestamp of the first packet in the pcap file.

The first argument is a template of the new filename. Use %% as a placeholder for the timestamp. Don’t forget the .pcap extension.

The next arguments are the pcap files to be renamed.
You can provide one or more pcap files, use wildcards (*.pcap) and use @file.
@file: file is a text file containing filenames. Each file listed in the text file is processed.

Example to rename pcap files:
pcap-rename.py server-%%.pcap *.pcap

Output:
Renamed: capture1.pcap -> server-20140416-184037-926493.pcap
Renamed: capture2.pcap -> server-20140417-114252-700036.pcap
Renamed: capture3.pcap -> server-20140419-052202-911011.pcap
Renamed: capture4.pcap -> server-20140424-065625-868672.pcap

Use option -n to view the result without actually renaming the pcap files.

This program does not support .pcapng files (yet).

pcap-rename_V0_0_1.zip (https)
MD5: 5F844411E178909970BC21349A629438
SHA256: AB706DB3470A915A3031EC248B8DAF83C08F42DBF6AC2EACB1A2DB2493B0AEEE

Thursday 4 June 2015

Regular Expressions With Comments

Filed under: My Software — Didier Stevens @ 20:01

Many flavors of regular expressions support comments now. You can make your regular expression a bit more readable by adding comments. Like in programming languages, where a comment does not change the behavior of the program, a regular expression comment does not change the behavior of the regular expression.

A regular expression comment is written like this: (?#comment) where comment can be any text, as long it is not ).

Here is an example of a regular expression for a simple email address: [A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,6}

And here is the same regular expression with a comment (bold): [A-Z0-9._%+-]+@(?#domain)[A-Z0-9.-]+\.[A-Z]{2,6}

Why am I posting this? Because I’m using this in my new Snort rules I’m blogging about soon.

Monday 18 May 2015

Howto: Install Wireshark Dissectors

Filed under: My Software,Wireshark — Didier Stevens @ 0:00

I teach a Wireshark class at Brucon 2015.

If you want to use my Wireshark dissectors like TCP Flag dissector, but don’t know how to install a Wireshark dissector, then watch this video howto:

Wednesday 6 May 2015

Update: NAFT Version 0.0.9

Filed under: Forensics,My Software,Networking,Update — Didier Stevens @ 13:55

This update to NAFT adds support for YARA. YARA rules can be used to search through the heap, like this:

naft-icd.py -y IOS_canary.yara –decoders decoder_xor1 heap r870-core

Address      Bytes     Prev     Next Ref     PrevF    NextF Alloc PC  what
83AB9498 0000004100 83AB9444 83ABA4CC 001  -------- -------- 80B5CC7C  8253709C
 YARA rule: IOS_canary

Rule IOS_canary.yara searches for a canary value inside the blocks.

rule IOS_canary
{
    strings:
        $canary = {FD 01 10 DF}
    condition:
        $canary
}

NAFT_V0_0_9.zip (https)
MD5: FEBBDB892D631275A95A0FEA59F8519F
SHA256: 95F42F109623F2BA6D8A9FFB013CBB0B5E995F02E5EB35F8E83A62B8CA8B86D0

Wednesday 29 April 2015

pdf-parser: A Method To Manipulate PDFs Part 2

Filed under: My Software,PDF — Didier Stevens @ 0:00

I provide 2 days of Hacking PDF training at HITB Amsterdam. This is one of the methods I teach.

Maarten Van Horenbeeck posted a diary entry (July 2008) explaining how scripts and data are stored in PDF documents (using streams), and demonstrated a Perl script to decompress streams. A couple of months before, I had started developing my pdf-parser tool, and Maarten’s diary entry motivated me to continue adding features to pdf-parser.

Extracting and decompressing a stream (for example containing a JavaScript script) is easy with pdf-parser. You select the object that contains the stream (example object 5: -o 5) and you “filter” the content of the stream (-f ). The command is:

pdf-parser.py –o 5 –f sample.pdf

In PDF jargon, streams are compressed using filters. You have all kinds of filters, for example ZLIB DEFLATE, but also lossy compressions like JPEG. pdf-parser supports a couple of filters, but not all, because the implementation of some of them (mostly the lossy ones) differs between vendors and PDF applications.

 

A recent article published by Virus Bulletin on JavaScript stored inside a lossy stream gave me the opportunity to implement a method I had worked out manually.

The problem: you need to decompress a stream and you have no decompression algorithm.

The solution: you use the PDF application to decompress the stream.

The method: you create a new PDF document with the stream as embedded file, and then save the embedded file using the PDF application.

The detailed method: when you need to decompress a stream for which you have no decompressor (or no decompressor identical to the target application), you create a new PDF document into which you include the object with the stream as an embedded file. PDF documents support embedded files. For example, if you have a PDF document explaining a financial method, you can include a spreadsheet in the PDF document as an embedded file. The embedded file is stored as an object with a stream, and the compression can be any method supported by the PDF application. Crafting this PDF document with embedded file manually requires many manipulations and calculations, and is thus a very good candidate for automation.

Figure: this PDF embeds a file called vbanner2.jpg

With pdf-parser, you can use this method as follows:

  1. Create a Python program that generates the PDF document with embedded file. Use pdf-parser like this (in this example, the data stream you want to decompress is in object 5 of PDF file sample.pdf): pdf-parser.py –generateembedded 5 sample.pdf > embedded.py
  2. Execute the Python program to create the PDF file: embedded.py embedded.pdf
  3. Open the created PDF file embedded.pdf with the target application (Adobe Reader for the Virus Bulletin example), and save the embedded file to disk
  4. The saved file contains the decompressed stream

You can find my PDF tools here.

Remark: the generated Python program requires my module mPDF.py, which can also be found on my PDF tools page.

Remark 2: don’t use this method when the stream contains an exploit for the decompressor.

Monday 27 April 2015

Update: virustotal-search Version 0.1.2 Daily Quota Handling and CVEs

Filed under: My Software,Update — Didier Stevens @ 0:00

This new version op virustotal-search adds a bunch of options to manage the local database, and 2 features I want to highlight here:

1) If you exceed your daily quota, virustotal-search will now do a clean stop. You can use option -w (waitquota) to instruct virustotal-search to wait until your daily quota is reset, and then continue. The quota reset is tested by doing a query every hour.

2) A new column was added to the CSV output: CVEs. virustotal-search will extract CVE numbers from AV detection signatures and report them in column CVEs.

And I also worked together with VirusTotal so that you get a proper error message when you submit an invalid search request (for example MD5 hash prefixed with $).

virustotal-search_V0_1_2.zip (https)
MD5: 62C8031738E6E20FEC38337010496DF6
SHA256: 317AF862A62CF78FC58604EDB77AA3C00EC1543D2337EC634749C25CC5E4908C

Thursday 16 April 2015

pdf-parser: A Method To Manipulate PDFs Part 1

Filed under: My Software,PDF,Update — Didier Stevens @ 0:00

I provide 2 days of Hacking PDF training at HITB Amsterdam. This is one of the methods I teach.

Sometimes when I analyze PDF documents (benign or malicious), I want to reduce the PDF to its essential objects. But when one removes objects in a PDF, indexes need to be updated and references updated/removed. To automate this process as much as possible, I updated my pdf-parser program to generate a Python program that in turn, generates the original PDF.

Thus when I want to make changes to the PDF (like removing objects), I generate its corresponding Python program, and then I edit this Python program.

I do this simply with option -g.

20150415-233047

Then you can edit the Python program, and when you run it, it will generate a new PDF file.

You can also use option -g together with option -f to filter the streams before they are inserted in the Python program. This gives you the decompressed streams in the Python program, opening them up to editing.

In this example, without option -f the Python statement for the stream object is:

oPDF.stream(5, 0, 'x\x9cs\nQ\xd0w3T02Q\x08IS040P0\x07\xe2\x90\x14\x05\r\x8f\xd4\x9c\x9c|\x85\xf0\xfc\xa2\x9c\x14M\x85\x90,\x05\xd7\x10\x00\xdfn\x0b!', '<<\r\n /Length %d\r\n /Filter /FlateDecode\r\n>>')

And with option -f, it becomes:

oPDF.stream2(5, 0, 'BT /F1 24 Tf 100 700 Td (Hello World) Tj ET', '', 'f')

The generated Python program relies on my mPDF library found in my PDF make tools.

pdf-parser_V0_6_2.zip (https)
MD5: D6717F1CA6B9DA2392E63F0DABF590DD
SHA256: 4DC0136062E9A5B6D84C74696005531609BD0299887B70DDFFAA19115BF2E746

Monday 13 April 2015

Update: oledump.py Version 0.0.14

Filed under: My Software,Update — Didier Stevens @ 0:00

A new version of oledump (small bugfix and updated plugins).

oledump_V0_0_14.zip (https)
MD5: 5ECD8BC3BD1F6C59F57E7C74DACCF017
SHA256: 7EEF509D84F7185C299A17882D3BD71481B7B1E41654F463F58492455FBDBD11

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