Didier Stevens

Wednesday 21 October 2009

A Windows 7 Launch Party Trick!

Filed under: Entertainment,Forensics,My Software,Windows 7 — Didier Stevens @ 17:19

In search of a new trick for that Windows 7 Launch Party you’re invited to? 😉

Here’s one:


You can download a beta version of my UserAssist tool here. Soon I’ll be posting a final version with details and source code.

Wednesday 14 October 2009

Update: WhoAmI? Version 0.1.3

Filed under: My Software,Update — Didier Stevens @ 18:00

I’ve updated my WhoAmI? Firefox add-on for Firefox version 3.5.

You can download it here or get it from the Mozilla site. I’ve nominated it to leave the Sandbox. If you use it, please post a review on the Mozilla page to help it on its way out of the the Sandbox (or keep it there if it’s too buggy).

Tuesday 13 October 2009

Update: PDFiD Version 0.0.9 to Detect Another Adobe 0Day

Filed under: My Software,PDF,Vulnerabilities — Didier Stevens @ 21:23

PDFiD is updated to detect the latest Adobe 0day, CVE-2009-3459.

I’ll provide more details in an upcoming post, just now for know that PDFiD detects a /Colors name followed by a very big number (larger than 2^24 or 16777216).


You can download PDFiD here.

Monday 5 October 2009

Preventing Applications From Starting (Malicious) Applications

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

Another very effective way to prevent malicious documents from infecting PCs, is to prevent vulnerable applications from starting other applications. As almost all shellcode found in malicious documents in-the-wild (again, I’m excluding targeted attacks) will ultimately start another process to execute the trojan, blocking this will prevent the trojan from executing.

This is an old idea you’ll find implemented in many sandboxes and HIPS. I added a new DLL to my basic process manipulation tool kit to prevent applications from creating a new process. Loading this DLL inside a process will prevent this process from creating a new process. I’ll explain the technique used in my DLL and how to load it in vulnerable applications in upcoming blogposts, but I want to start with showing how it prevents malicious documents from infecting a PC.

When the DLL is loaded inside a process, it will patch the Create Process API to intercept and block calls to it:


As a first test, we’ll use my eicar.pdf document.


Clicking the button will save the eicar.txt file to a temporary folder and launch the editor.

Adobe Acrobat reader will warn you when an application is to be launched:


But when you accept, the editor will be prevented to execute:


That’s because the DLL intercepted and blocked the Create Process call:


As a second test, let’s use a real malicious PDF document. The hooks installed by the DLL prevent it from executing the trojan:


Adobe Reader starts and then just crashes, without spawning another process:


When opening the same malicious PDF, but without the protecting DLL, the machine gets trojaned (execution of 1.exe and Internet Explorer):


This simple way of preventing applications from launching other applications comes with some drawbacks. For example, the Check Update function in Adobe Reader will not function anymore.

When you have a sandboxing system of HIPS installed on the machines you manage, check if you can use it to prevent vulnerable applications from starting other applications. If it doesn’t provide such a feature, try the new DLL I’ll be posting in the new version of bpmtk.

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