A new tool, a new video:
base64dump_V0_0_1.zip (https)
MD5: 350C12F677E08030E0DD95339AC3604D
SHA256: 1F8156B43C8B52B7E5620B7A8CD19CFB48F42972E8625994603DDA47E07C9B35
Sunday 5 July 2015
base64dump.py Version 0.0.1
Friday 26 June 2015
Update: oledump.py Version 0.0.17 – ExitCode
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 16 June 2015
Metasploit Meterpreter Reverse HTTPS Snort Rule
Emerging Threats and Snort released my Snort rule to detect Metasploit Meterpreter Reverse HTTPS traffic.
More details about the rule in an upcoming blogpost.
Tuesday 9 June 2015
pcap-rename.py
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
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
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:
Monday 11 May 2015
Detecting Network Traffic from Metasploit’s Meterpreter Reverse HTTP Module
I teach a Wireshark class at Brucon 2015.
I took a closer look at Metasploit’s Meterpreter network traffic when reverse http mode is used.
The Meterpreter client will make regular HTTP requests to the Metasploit server to check if it has commands ready to be executed. This is how a request looks like:
The client sends an HTTP POST request with a 4-byte payload: RECV. The URI has the following pattern: 4 or 5 alphanumeric characters, an underscore and 16 alphanumeric characters. The 16 alphanumeric characters are chosen at random, and the 4 or 5 alphanumeric characters are some kind of checksum.
I checked Meteasploit’s source code: these characteristics of Meterpreter’s Reverse HTTP protocol are hardcoded.
What is not hardcoded, but parametrized with a variable, is the User Agent String. By default, it is “Mozilla/4.0 (compatible; MSIE 6.1; Windows NT)”, but it is an option that can be changed.
I’ve tested the detection of Metasploit Meterpreter traffic with this User Agent String in several environments, and never encountered a false positive. You might think that “Mozilla/4.0 (compatible; MSIE 6.1; Windows NT)” is quite common as a User Agent String, but it is not. “MSIE 6.1” is pretty rare (according to Wikipedia, there is no Internet Explorer version 6.1), and “Windows NT” without version number is also rare. Combined, I’ve never seen this User Agent String except for Metasploit Meterpreter traffic. The only User Agent String seen in-the-wild that comes close to this one is “Mozilla/4.0 (compatible; MSIE 6.1; Windows XP)”. But I suggest that you check your environment for this Metasploit User Agent String if you want to be sure no false positives will be generated in your environment.
But like I said, the User Agent String is an option, and can be easily changed by the Metasploit operator. That’s why I also developed a method to detect Metasploit Meterpreter Reverse HTTP traffic looking for its hardcoded characteristics: a POST request with RECV payload to a recognizable URI.
Here is the Snort rule:
# Snort rules by Didier Stevens (http://DidierStevens.com)
# 2015/05/01 - 2015/05/10
# Thanks to Nathan Fowler for helping out with performance optimization
# I start numbering my rules at SID 1618000
alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"Metasploit Meterpreter"; flow:to_server,established; content:"RECV"; http_client_body; depth:4; fast_pattern; isdataat:!0,relative; urilen:23<>24,norm; content:"POST"; pcre:"/^\/[a-z0-9]{4,5}_[a-z0-9]{16}\/$/Ui"; classtype:trojan-activity; reference:url,blog.didierstevens.com/2015/05/11/detecting-network-traffic-from-metasploits-meterpreter-reverse-http-module/; sid:1618008; rev:1;)
This Snort rule looks for traffic from your internal network to the outside. You need to change the rule if you want to detect internal-only traffic.
Here is an example of an alert:
[**] [1:1618008:1] Metasploit Meterpreter [**] [Classification: A Network Trojan was detected] [Priority: 1] 05/11-22:26:31.236007 192.168.174.1:54949 -> 192.168.174.137:80 TCP TTL:64 TOS:0x0 ID:21177 IpLen:20 DgmLen:212 DF ***A**** Seq: 0x1B677291 Ack: 0x861008DD Win: 0x7680 TcpLen: 20 [Xref => https://blog.didierstevens.com/2015/05/11/detecting-network-traffic-from-metasploits-meterpreter-reverse-http-module/]
Based on the Metasploit User Agent Strings I published a couple of months ago, I made these Snort rules:
# Snort rules by Didier Stevens (http://DidierStevens.com)
# 2015/04/30
# I start numbering my rules at SID 1618000
#alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"Metasploit User Agent String"; flow:to_server,established; content:"User-Agent|3a| Mozilla/4.0 (compatible\; MSIE 6.0\; Windows NT 5.1)|0d 0a|"; http_header; classtype:trojan-activity; reference:url,blog.didierstevens.com/2015/03/16/quickpost-metasploit-user-agent-strings/; sid:1618000; rev:1;)
alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"Metasploit User Agent String"; flow:to_server,established; content:"User-Agent|3a| Mozilla/4.0 (compatible\; MSIE 6.1\; Windows NT)|0d 0a|"; http_header; classtype:trojan-activity; reference:url,blog.didierstevens.com/2015/03/16/quickpost-metasploit-user-agent-strings/; sid:1618001; rev:1;)
#alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"Metasploit User Agent String"; flow:to_server,established; content:"User-Agent|3a| Mozilla/4.0 (compatible\; MSIE 7.0\; Windows NT 6.0)|0d 0a|"; http_header; classtype:trojan-activity; reference:url,blog.didierstevens.com/2015/03/16/quickpost-metasploit-user-agent-strings/; sid:1618002; rev:1;)
alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"Metasploit User Agent String"; flow:to_server,established; content:"User-Agent|3a| Mozilla/4.0 (compatible\; MSIE 7.0\; Windows NT 6.0\; Trident/4.0\; SIMBAR={7DB0F6DE-8DE7-4841-9084-28FA914B0F2E}\; SLCC1\; .N|0d 0a|"; http_header; classtype:trojan-activity; reference:url,blog.didierstevens.com/2015/03/16/quickpost-metasploit-user-agent-strings/; sid:1618003; rev:1;)
alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"Metasploit User Agent String"; flow:to_server,established; content:"User-Agent|3a| Mozilla/4.0 (compatible\; Metasploit RSPEC)|0d 0a|"; http_header; classtype:trojan-activity; reference:url,blog.didierstevens.com/2015/03/16/quickpost-metasploit-user-agent-strings/; sid:1618004; rev:1;)
#alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"Metasploit User Agent String"; flow:to_server,established; content:"User-Agent|3a| Mozilla/5.0 (Windows\; U\; Windows NT 5.1\; en-US) AppleWebKit/525.13 (KHTML, like Gecko) Chrome/4.0.221.6 Safari/525.13|0d 0a|"; http_header; classtype:trojan-activity; reference:url,blog.didierstevens.com/2015/03/16/quickpost-metasploit-user-agent-strings/; sid:1618005; rev:1;)
alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"Metasploit User Agent String"; flow:to_server,established; content:"User-Agent|3a| Mozilla/5.0 (compatible\; Googlebot/2.1\; +http://www.google.com/bot.html)|0d 0a|"; http_header; classtype:trojan-activity; reference:url,blog.didierstevens.com/2015/03/16/quickpost-metasploit-user-agent-strings/; sid:1618006; rev:1;)
#alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"Metasploit User Agent String"; flow:to_server,established; content:"User-Agent|3a| Mozilla/5.0 (compatible\; MSIE 10.0\; Windows NT 6.1\; Trident/6.0)|0d 0a|"; http_header; classtype:trojan-activity; reference:url,blog.didierstevens.com/2015/03/16/quickpost-metasploit-user-agent-strings/; sid:1618007; rev:1;)
Remark that I commented-out the Snort rules that I expect to generate too many false positives. But it’s best that you check what User Agent Strings are common in your environment, before you deploy and uncomment these rules.
Update: these rules are designed for an environment where egress traffic has to go to an HTTP port. If your environment allows all destination ports (like Metasploit’s default 4444 port), then replace $HTTP_PORTS by any in the rules you deploy. Thanks @securitygen for the remark.
snort-rules-V0_0_1.zip (https)
MD5: 526AAC1CE1E8576633498223DFA07E3D
SHA256: 7694E4E884E12068BC2A32714D3B0C48060B12C80E4093AFB6B1563E2EDA5E8D
Wednesday 6 May 2015
Update: NAFT Version 0.0.9
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
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:
- 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
- Execute the Python program to create the PDF file: embedded.py embedded.pdf
- 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
- 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
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
Didier Stevens 