New VAC exploit detection reads & reports users DNS cache

[DrunknMunky Veteran]

Decompiled module: http://i.imgur.com/z9dppCk.png

 

What it does:

• Goes through all your DNS Cache entries (ipconfig /displaydns)

• Hashes each one with md5

• Reports back to VAC Servers

• So the domain reddit.com would be 1fd7de7da0fce4963f775a5fdb894db5 or organner.pl would be 107cad71e7442611aa633818de5f2930 (Although this might not be fully correct because it seems to be doing something to characters between A-Z, possible making them lowercase)

• Hashing with md5 is not full proof, they can be reversed easily nowadays using rainbowtables. So they are relying on a weak hashing function

You dont have to visit the site, any query to the site (an image, a redirect link, a file on the server) will be added to the dns cache. And only the domain will be in your cache, no full urls. Entries in the cache remains till they expire or at most 1 day (might not be 100% accurate), but they dont last forever.

 

We don't know how long this information is kept on their servers, maybe forever, maybe a few days. It's probably done everytime you join a vac server. It seems they are moving from detecting the cheats themselves to computer forensics. Relying on leftover data from using the cheats. This has been done by other anticheats, like punkbuster and resulted in false bans. Although im not saying they will ban people from simply visiting the site, just that it can be easily exploited

 

EDIT1: To replicate this yourself, you will have to dump the vac modules from the game. Vac modules are streamed from vac servers and attach themselves to either steamservice.exe or steam.exe (not sure which one). Once you dump it, you can load the dll into ida and decompile it yourself, then reverse it to find the winapi calls it is using and come to the conclusion yourself. There might be software/code out there to dump vac modules. But its not an easy task. And on a final note, you shouldn't trust anyone with your data, even if its valve. At the very least they should have a clear privacy policy for vac.

 

http://www.reddit.com/r/GlobalOffensive/comments/1y0kc1/vac_now_reads_all_the_domains_you_have_visited/

 

[DrunknMunky Veteran]

GabeN made a surprising post over on Reddit to explain more on this:

 

 

Trust is a critical part of a multiplayer game community - trust in the developer, trust in the system, and trust in the other players. Cheats are a negative sum game, where a minority benefits less than the majority is harmed.

 

There are a bunch of different ways to attack a trust-based system including writing a bunch of code (hacks), or through social engineering (for example convincing people that the system isn't as trustworthy as they thought it was).

 

For a game like Counter-Strike, there will be thousands of cheats created, several hundred of which will be actively in use at any given time. There will be around ten to twenty groups trying to make money selling cheats.

 

We don't usually talk about VAC (our counter-hacking hacks), because it creates more opportunities for cheaters to attack the system (through writing code or social engineering).

 

This time is going to be an exception.

 

There are a number of kernel-level paid cheats that relate to this Reddit thread[1] . Cheat developers have a problem in getting cheaters to actually pay them for all the obvious reasons, so they start creating DRM and anti-cheat code for their cheats. These cheats phone home to a DRM server that confirms that a cheater has actually paid to use the cheat.

 

VAC checked for the presence of these cheats. If they were detected VAC then checked to see which cheat DRM server was being contacted. This second check was done by looking for a partial match to those (non-web) cheat DRM servers in the DNS cache. If found, then hashes of the matching DNS entries were sent to the VAC servers. The match was double checked on our servers and then that client was marked for a future ban. Less than a tenth of one percent of clients triggered the second check. 570 cheaters are being banned as a result.

 

Cheat versus trust is an ongoing cat-and-mouse game. New cheats are created all the time, detected, banned, and tweaked. This specific VAC test for this specific round of cheats was effective for 13 days, which is fairly typical. It is now no longer active as the cheat providers have worked around it by manipulating the DNS cache of their customers' client machines.

 

Kernel-level cheats are expensive to create, and they are expensive to detect. Our goal is to make them more expensive for cheaters and cheat creators than the economic benefits they can reasonably expect to gain.

 

There is also a social engineering side to cheating, which is to attack people's trust in the system. If "Valve is evil - look they are tracking all of the websites you visit" is an idea that gets traction, then that is to the benefit of cheaters and cheat creators. VAC is inherently a scary looking piece of software, because it is trying to be obscure, it is going after code that is trying to attack it, and it is sneaky. For most cheat developers, social engineering might be a cheaper way to attack the system than continuing the code arms race, which means that there will be more Reddit posts trying to cast VAC in a sinister light.

 

Our response is to make it clear what we were actually doing and why with enough transparency that people can make their own judgements as to whether or not we are trustworthy.

 

Q&A

1) Do we send your browsing history to Valve? No.

2) Do we care what porn sites you visit? Oh, dear god, no. My brain just melted.

3) Is Valve using its market success to go evil? I don't think so, but you have to make the call if we are trustworthy. We try really hard to earn and keep your trust.

 

 

http://redd.it/1y70ej

[trag3dy]

That's funny that the cheaters need to have DRM to protect their cheat software. The future is where cheaters need to pirate their cheat software. Not that I have any sympathy for the people who make the cheats anyways. If ever there was a software that deserved to be pirated..