Speed up your fuzzfarm: fast hit tracing

11/05/2012 12 comments

The fuzzing methodology introduced by Charlie Miller [1] was widely adopted in the security industry, as it is indeed an effective and low cost method of finding bugs.

The idea is:

  • collect a lot of sample files
  • let your target application parse them all
  • collect the set of basic blocks executed for every file
  • calculate the minimal set of samples that covers all of the collected basic blocks
  • flip random bytes in files from that set and wait for a crash

It’s a simple process, but all implementations I heard of suffer from an interesting performance bottleneck in the basic block tracing part.

If your tracer takes >1min per file, you can speed it up to take only few seconds, with just a few simple observations.

Read more…

Exploiting CVE-2011-2371 (FF reduceRight) without non-ASLR modules

22/02/2012 2 comments

CVE-2011-2371 (found by Chris Rohlf and Yan Ivnitskiy) is a bug in Firefox versions <= 4.0.1. It has an interesting property of being a code-exec and an info-leak bug at the same time. Unfortunately, all public exploits targeting this vulnerability rely on non-ASLR modules (like those present in Java).

In this post I’ll show how to exploit this vulnerability on Firefox 4.0.1/Window 7, by leaking imagebase of one of Firefox’s modules, thus circumventing ASLR without any additional dependencies.

Read more…

Hyperelliptic curve crypto — Dcoder’s keygenme #2

26/09/2011 2 comments

Apparently ordinary elliptic curves in crackmes are getting boring, so Dcoder decided to make things interesting with hyperelliptic curves. Due to intricate nature of HE curves, performing computations on them is more expensive, than for ordinary curves, but on the other hand HE curves provide superior bitstrength security, with regard to size of the base field, they are defined over.

In this blog post, I will try to introduce HE curves, and how to use them in crypto. Using that knowledgle, it will be easy to analyze and break a signature scheme implemented in keygenme #2 by Dcoder. Note that this won’t be a rigorous mathematical dissertation, but a “tutorial” for mathematically inclined programmer :).

Read more…

Universal ROP shellcode for OS X x64

23/07/2011 12 comments

One of the hurdles one will encounter during OS X exploitation is ASLR/DEP combination for 64-bit processes (32bit don’t have DEP [1]). When implemented correctly, it’s an effective mitigation, which can be circumvented only with an info leak. (Un)fortunately, OS X versions up to recent Lion (10.7) offer only incomplete ASLR which still allows attackers to succeed in their efforts to execute arbitrary code. One of the problems (among others) is dyld (dynamic loader) image being located at the same address in every process. This makes ROP possible — by controlling the stack, we can reuse snippets of code from dyld and, in effect, execute arbitrary code.

The only public ROP dyld shellcode for OS X was presented in [1]. Charlie Miller’s version works under the assumption that that rax/rdi have specific values. Due to x64 calling convention [2] it is very probable that this precondition is met. Nevertheless it would be useful to create a shellcode with weaker assumptions — that’s exactly what this post is about. We will create a generic ROP shellcode, similiar to sayonara, but for OS X :).

Read more…

Dongles and Nyberg-Rueppel signature scheme

10/07/2011 3 comments

“Dongle me” by cyclops is, as name suggest, a crackme that requires a hardware dongle, or a software emulator. These two technical problems, combined with an uncommon authentication scheme, make it an interesting target to analyse.

Read more…

Solving confidence 2011 crackme for fun and profit

26/06/2011 3 comments

Confidence is a security conference organized in Poland. During this year’s edition (and like during few previous editions) a crackme contest took place — attendees were invited to provide a solution (serial, keygen). The fastest one would win the prize (pocketbook reader).

Read more…

Solving Pimp crackme by j00ru and Gynvael Coldwind

24/06/2011 9 comments

I figured a nice tutorial would be more interesting than yet another “hello world” post, so here it goes — solution for Pimp crackme, a winning entry for Pimp my crackme contest (polish) by j00ru and Gynvael. You can download entires (all three of them) from the contest’s page. AFAIK I’m the only person who submitted a solution.

Let’s see what we are up against.

Looks nice :).

Read more…