Pi-hole vulnerabilities

Pi-hole, a DNS sinkhole system, has a vulnerability in shell scripts that perform file operations with root privileges without validating paths. An attacker with Pi-hole privileges can exploit this flaw to escalate privileges to root by manipulating SSH keys.

In Pi-hole from 6.4.2 until 6.5, the root-run updatecheck.sh cron job applies truncate -s 0 and chmod 644 to /etc/pihole/versions while following symbolic links in a directory owned by the pihole user. An attacker running as pihole can replace the path with a symlink so the scheduled root operations truncate or create an arbitrary root-owned file, or race them so chmod makes a sensitive target world-readable.

In Pi-hole prior to 6.5, getFTLPID() in utils.sh validates the pihole-owned /run/pihole-FTL.pid file with expr, rejecting only values whose first character is not a digit. An attacker with code execution as pihole can write a digit-prefixed arithmetic expression that Bash then evaluates as root, enabling command substitution execution.

In Pi-hole prior to 6.5, gravity.sh checks file:// adlist readability with sudo -u pihole test -r but then allows curl, sometimes running as root, to normalize URL dot segments and open a different file. A pihole-readable decoy can therefore pass the check while curl reads a root-only target, and /proc/self paths can similarly resolve against different processes.

A vulnerability in Pi-hole versions 6.0 to 6.4.2 allows a user with code execution as the unprivileged pihole user to escalate privileges to root by replacing the /etc/pihole/logrotate file. The file is then processed by pihole-FTL-prestart.sh, which changes its ownership to root:root, and subsequently executed as root by the daily pihole flush cron, enabling arbitrary code execution with administrative privileges.