pastebin.com is a wonderful website. I'm scrapping all posted pasties (not only from pastebin.com) and pass them to a bunch of regular expressions. As I said in a previous diary[1], it is a good way to perform open source intelligence. Amongst many configuration files, pieces of code with hardcoded credentials, dumps of databases or passwords, sometimes it pays and you find more interesting data.

For a few days, I'm finding many pasties that contain only Base64 data. The decoded data are malicious PE files. Some files were posted multiple times, others were unique. Some examples from my list:

• hxxp://pastebin.com/cW0zR4St
• hxxp://pastebin.com/QTEd5Eqe
• hxxp://pastebin.com/Zfhtnk9X
• hxxp://pastebin.com/nVRhzRxJ
• hxxp://pastebin.com/8U5beggH

Most of the malicious files are known on VT (submitted a few hours ago), others are unknown. I also detected some obfuscated pasties:The Base64 code is reversed:

• hxxp://pastebin.com/C7YYaUZB

Another technique is the hex-encode the Base64 data:

• hxxp://pastebin.com/GeNX7DYP
• hxxp://pastebin.com/15en56ZE

This technique has already been seen in the past[2]. Powershell or Javascript scripts download malicious content from pastebin.com. But, until now, I was not able to find any reference to the pasties above. Please share with us if you have more information!

In the meantime, it could be a good idea to keep an eye on your logs and search for HTTP requests to these URLs (or globally to pastebin.com if this service is not used in your environment).

[1] https://isc.sans.edu/forums/diary/Hunting+for+Juicy+Information/20555
[2] https://blog.malwarebytes.com/cybercrime/2016/10/get-your-rat-on-pastebin/

Xavier Mertens (@xme)
ISC Handler - Freelance Security Consultant
PGP Key