Multiple vulnerabilities in csDoom 0.7

Type securityvulns
Reporter Securityvulns
Modified 2006-03-27T00:00:00


                         Luigi Auriemma

Application: client/server Doom (csDoom) (current maintainer) (original author, 2000) Versions: <= 0.7 Platforms: Windows, nix, BSD and more Bugs: A] buffer-overflow in SV_BroadcastPrintf B] buffer-overflow in SV_SetupUserInfo C] format string in Printf Exploitation: A] remote, versus server B] remote, versus server C] remote, versus server and client Date: 26 March 2006 Author: Luigi Auriemma e-mail: web:

1) Introduction 2) Bugs 3) The Code 4) Fix

=============== 1) Introduction ===============

client/server Doom (csDoom) is an open source Doom engine developed by Sergey Makovkin and based on the ZDoom 1.22 code. The game is focused on online multiplayer and the latest version has been released in the far year 2000.

In the 2004/2005 Denis Lukianov decided to continue the development of this engine focusing moreover on the removing of all the bugs which caused the death of this software.

Although enough old, this game is still included in the Internet Doom Explorer (IDE, server browser used to retrieve the online servers list of some multiplayer Doom engine.

======= 2) Bugs =======

A] buffer-overflow in SV_BroadcastPrintf

The function SV_BroadcastPrintf is used by the server for sending a message to all the connected clients. For example it's used when a client joins the match or when he sends a chat message. The buffer used for containing the generated string is composed by 1024 bytes while the input text sent from the attacker can be max 2048 bytes long (MSG_ReadString) allowing possible malicious code execution.

From doomsv/src/sv_main.cpp:

void STACK_ARGS SV_BroadcastPrintf (int level, const char fmt, ...) { va_list argptr; char string[1024]; client_t cl;

va_start &#40;argptr,fmt&#41;;
vsprintf &#40;string, fmt,argptr&#41;;
va_end &#40;argptr&#41;;

B] buffer-overflow in SV_SetupUserInfo

When a player joins the server he sends two text strings which identify his nickname and teamname. Both these strings (max 2048 bytes, MSG_ReadString) are copied through strcpy() in two buffers of 16 bytes. Anyway these buffers are global, not local, so should be not possible to use this bug for executing malicious code but only for crashing the server.

From doomsv/src/sv_main.cpp:

void SV_SetupUserInfo(void) { player_t *p;

p = &amp;players[parse_cl];

strcpy&#40;p-&gt;userinfo.netname, MSG_ReadString&#40;&#41; &#41;;
strcpy&#40;p-&gt;, MSG_ReadString&#40;&#41; &#41;;

C] format string in Printf

Both client and server have the same format string vulnerability in the PrintString function (in the instruction "printf (outline);") located in doom*/src/c_console.cpp. This function is used for visualizing all the text strings in the console and in the game screen through the Printf function, widely used in the engine. The following code flow should be enough clear:

int STACK_ARGS Printf (int printlevel, const char *format, ...) { va_list argptr; int count;

va_start &#40;argptr, format&#41;;
count = VPrintf &#40;printlevel, format, argptr&#41;;
va_end &#40;argptr&#41;;

return count;


int VPrintf (int printlevel, const char *format, va_list parms) { char outline[8192];

if &#40;gameisdead&#41;
    return 0;

vsprintf &#40;outline, format, parms&#41;;
return PrintString &#40;printlevel, outline&#41;;


int PrintString (int printlevel, const char *outline) { printf (outline); return strlen (outline); }

Note: this bug has been already patched by Denis in the csDoom client.

=========== 3) The Code ===========

====== 4) Fix ======

All the bugs have been fixed in the current version (released yesterday) maintained by Denis: