[SANS ISC] BASE85 Decoding With base64dump.py, (Sat, Jul 17th)

Xavier’s diary entry “Multiple BaseXX Obfuscations” covers a malicious script that is encoded with different “base” encodings. Xavier starts with my tool base64dump.py, but he can not do the full decoding with base64dump, as it does not support BASE85.

I’ve now added support for BASE85: base64dump.py version

(you can watch this video: “Adding BASE85 To basedump64.py“, if you are interested to know what changes I made to my base64dump.py tool to support BASE85)

So, let’s see how to use base64dump with Xavier’s sample. As Xavier showed yesterday, this sample has the payload encoded as a list of hexadecimal string. So let’s do hex decoding with base64dump: option -e hex. And option -n 10 for a minimum length of 10:

base64dump found 21 hexadecimal strings, with a minimal decoded length of 10.

These strings have to be concatenated together. We can achieve this with base64dump, by ignoring all whitespace (including newlines) and ignoring the string quotes (single quote ‘), like this:

Now we have extracted one single, long hexadecimal string. Let’s selected and decode it:

This is again an hexadecimal string. Let’s decode it with another instance of base64dump:

And this is the BASE85 encoded script. Let’s decode that too:

And we end up with the same decoded script as Xavier found yesterday.

Didier Stevens
Senior handler
Microsoft MVP

(c) SANS Internet Storm Center. https://isc.sans.edu Creative Commons Attribution-Noncommercial 3.0 United States License.

Source: Read More (SANS Internet Storm Center, InfoCON: green)

You might be interested in …

[BleepingComputer] Microsoft: SEO poisoning used to backdoor targets with malware

Microsoft is tracking a series of attacks that use SEO poisoning to infect targets with a remote access trojan (RAT) capable of stealing the victims’ sensitive info and backdooring their systems. […] Source: Read More (BleepingComputer)

Read More

[ZDNet] Telstra, Optus, and Aldi Mobile warned by ACMA for not verifying new customer info

All posts, ZDNet

ACMA states it is ‘cracking down’ on telcos leaving customers vulnerable to identity theft, with Telstra, Aldi Mobile, and Optus in the firing line. Source: Read More (Latest topics for ZDNet in Security)

Read More

[SecurityWeek] Hackers Claim to Have Data of 70 Million AT&T Customers

All posts, Security Week

A hacking group claims to be in the possession of a database containing private information on roughly 70 million AT&T customers, but the telecoms company says its systems have not been breached. read more Source: Read More (SecurityWeek RSS Feed)

Read More

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.