It has no knowledge of the BSP file format or of the target Through fuzzing VLC when it used to be called Failure Observation Engine (FOE).īFF is a simple “dumb” fuzzer, meaning it merely corrupts bytes in the file and I also had some relevant experience with the framework This proved to be an excellent choice due to its easy configuration file andĭeep integration with Microsoft debugging tools, including WinDBG and In the end I gave up trying to get a coverageīased fuzzer to work and went instead with the solid CERT Basic Fuzzing Led to a multi-day rabbit hole of building DynamicRIO from source and Work due to some binary incompatibilities and possible Windows 10 issues.

Proved to be completely broken for crash detection. I had a few false starts to this project when selecting a fuzzer to use. It’s even possible that stored sizes of data structures in the BSP file will be less validated than most file formats. BSP would map quite well to low-level memcpy operations in the engine. I figured that highly complex file formats such as. If a crash is found, it is recorded and stored for later triage and classification. This will corrupt them and then feed them back in to the program (CZ) to be parsed while being watched for any crashes. My approach to finding bugs was to use the tried and true method of fuzzing.Įssentially I gathered a bunch of existing BSP map files for my corpus and then used them as seeds to my fuzzing engine. I certainly look forward to disclosing to Valve in the future. The whole process, from initial email to fix, lasted less than 30 days. I would like to extend my thanks to the Valve Security team and specifically to Alfred Reynolds who was my liaison during the disclosure process. The vulnerability discussed in this article has been disclosed to Valve Security and the patch publicly deployed on July 10th. This automatic resource fetching looked like the ticket to a remotely exploitable vulnerability via a local file. Only then will the client begin receiving commands and entity updates from the server. Once all of the resources have been downloaded, they have to be loaded and parsed from disk into memory. Upon connecting to the server, the game client will automatically download any required resources (maps, textures, sounds, etc.).

What makes Counter Strike an interesting target is that it relies on a game lobby for players to find and select servers to play on. Condition Zero, Half-Life 1, and CS 1.6 all run on the GoldSrc engine, which was created by Valve and is based upon the original Quake engine. One night while playing Counter Strike: Condition Zero (CZ), I decided to take a break and challenge myself to find an exploitable bug in the old engine known as GoldSrc.

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