[ANY] SRCDS Server Crasher Exploit Patch [6/27/19]
 

There's a new exploit in the wild which allows any client to attack the server after connecting if you have sv_allowdownload set to 1. On Linux the servers will most likely restart within 30 seconds if there's a watchdog timer installed. On Windows this exploit can be utilized to cause a Blue Screen Of Death on your dedicated hosters box. The exploit involves the use of the RequestFile command and has already been reported to Valve (~8 Months ago) through the bounty bug reward program. The report was ignored by the HackerOne Staff because it didnt meet the standards of "crashing the server" ( Report #472858 ). Even though this can lead to a BSOD if used correctly and as shown in my submited Proof Of Concept. ...

The exploit's POC was stolen from one of my un-secured dedicated test servers recently by some "Hackers" and now is being sold by them. The POC was written to work on all versions of SRCDS so many servers are at risk until valve releases an official patch. I've written my own patch for the community to use until that date comes.

Symptoms of the exploit being used on your server would be to see the text "File '%s' requested from" spammed in your SRCDS console. These messages do not create logs in any document so it may be hard for some users to track what's happening. This is mostly expected to plauge CS:GO/CStrike servers currently.

I've only tested this on css/csgo and it seems to work fine. I'm unaware if any game mode will utilize the request file function after a player conects (for example sprays) but i believe it's handled differently (server sends files rather than client requesting file). Let me know if you run into any issues.

Edit: Added OnFileReceive Hook as well to prevent clients from spamming file sends to the server. Nopped out a message that still prints on file receive when the server has sv_allowupload set to 0 (Untested Changes) Updated 1/2/2021, Please post a report if it crashes on linux or windows CSGO servers


Updated 02/03/2023:
Untested, updated for linux changes.

Newest version: SendFileFix 3.3.zip

Re: [ANY] SRCDS Server Crasher Exploit Patch [6/27/19]
 

Eggcellent

Re: [ANY] SRCDS Server Crasher Exploit Patch [6/27/19]
 

what a server being crashed from console looks like:
https://i.imgur.com/TsBVrI9.png


https://www.youtube.com/watch?v=fMo_Au6QqBo
me doing it

Re: [ANY] SRCDS Server Crasher Exploit Patch [6/27/19]
 

why exactly 32?

iterating through 32 entities and checking if <= is wrong, you should start your for loop with 1 for that, there's no '0' client (let me mention i might be wrong, not sure)

after some lines you do the same exact thing but correctly, you should always start with 1 if you're checking <=

anyways, i didnt find any other wrong code besides that

Re: [ANY] SRCDS Server Crasher Exploit Patch [6/27/19]
 

Console is entity 0, although I'm not sure if it's a oversight or the console can play a role in this exploit.

Also to note, MaxClients variates depending on the number of clients the server can accept, so it could be iterating through 10, 32, 64 or whatever number of players the server is set up to.

Re: [ANY] SRCDS Server Crasher Exploit Patch [6/27/19]
 

why does the plugin loop through all clients every 5 seconds and subtract 32 from their RequestCount?


edit: I'm guessing it's to account for false-positive scenarios in case there's a game mode that happens to send a large amount of files:

Re: [ANY] SRCDS Server Crasher Exploit Patch [6/27/19]
 

Oh shit man, I feel sorry for you to get your work stolen and not even recognized.

Re: [ANY] SRCDS Server Crasher Exploit Patch [6/27/19]
 

Yes exactly, some game modes will send player sprays/jingle sound after a client is actively in the server. This will prevent a server of 64 slot players with all custom sprays and no map changes causing false postives from happening. When a new client connects on the same map it will count towards the requestcount.

Re: [ANY] SRCDS Server Crasher Exploit Patch [6/27/19]
 

:?: :?: :?:

Re: [ANY] SRCDS Server Crasher Exploit Patch [6/27/19]
 

In csgo you just need to use sv_allowdownload 0 and sv_allowupload 0.

This exploit has been running since 2018.