Wednesday, November 18, 2009

Heap Spraying with Actionscript by FireEye and From Targeted PDF Attack to Backdoor in Five Stages y McAfee

FireEye Malware Intelligence Lab
Julia Wolf @ FireEye Malware Intelligence Lab

Heap Spraying with Actionscript

Why turning off Javascript won't help this time

As you may have heard, there's a new Adobe PDF-or-Flash-or-something 0-day in the wild. So this is a quick note about how it's implemented, but this blog post is not going to cover any details about the exploit itself.

Background Summary

Most of the Acrobat exploits over the last several months use the, now common, heap spraying technique, implemented in Javascript/ECMAscript, a Turing complete language that Adobe thought would go well with static documents. (Cause that went so well for Postscript) (Ironically, PDF has now come full circle back to having the features of Postscript that it was trying to get away from.) The exploit could be made far far less reliable, by disabling Javascript in your Adobe Acrobat Reader.

But apparently there's no easy way to disable Flash through the UI. US-CERT recommends renaming the “%ProgramFiles%\Adobe\Reader 9.0\Reader\authplay.dll” and “%ProgramFiles%\Adobe\Reader 9.0\Reader\rt3d.dll” files. [Edit: Actually the source for this advice is the Adobe Product Security Incident Response Team (PSIRT).]

Anyway, here's why… Flash has it's own version of ECMAScript called Actionscript, and whoever wrote this new 0-day, finally did something new by implementing the heap-spray routine with Actionscript inside of Flash. More

McAfee Labs Blog
          From Targeted PDF Attack to Backdoor in Five Stages
          Monday September 14, 2009 at 12:33 pm CST
          Posted by Dennis Elser

 As reported by Adobe in July, a Flash vulnerability is being actively exploited by targeted attacks against Adobe Reader. Yes, embedding Flash movies in PDF documents is supported in Adobe Acrobat 9. The idea of allowing Flash movies to be displayed within PDFs isn’t bad if you like your documents spiced up with a bit of interactivity or training videos. From a security perspective, however, this poses yet another attack vector for criminals to take control of vulnerable systems. As history has shown, complexity and feature richness go hand in hand with remotely exploitable vulnerabilities. It is unfortunately no different with this latest PDF feature.

The exploitation of this vulnerability continues. Below are screenshots from one such malicious PDF document, discovered in a targeted attack this week. The attack contains several compressed streams and at least two embedded Flash movies. The first embedded Flash movie is clean, the second 6exploits CVE-ID 2009-1862, which causes a memory corruption and allows an attacker’s code to execute. Underneath the compression layer, JavaScript code is embedded in the PDF document. This code fills heap memory with the attacker’s shellcode. Apart from the PDF acting as an additional obfuscation layer around the exploit, the JavaScript code, once unpacked, contains another function that attempts to evade detection. More

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