Pi-hole: arbitrary root file clobber / chmod / disclosure via updatecheck.sh cron following /etc/pihole/versions symlink

Summary

Pi-hole is a DNS sinkhole that protects devices from unwanted content without installing any client-side software. From 6.4.2 until 6.5, the root-run advanced/Scripts/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 executing as pihole can replace that path with a symlink so the scheduled root operations truncate or create an arbitrary root-owned file, or race the operations so chmod makes a sensitive target world-readable without truncating it. This issue is fixed in version 6.5.

Remediation

1. Inventory every pi-hole pi-hole deployment, including staging.
2. No fixed version appears in the public sources yet. Check the references below and the vendor directly.

References

• Referencehttps://github.com/pi-hole/pi-hole/commit/85de82dd2b63bf71ecb936177dfb82421d9d2f25
• Referencehttps://github.com/pi-hole/pi-hole/commit/c1062f43b0de1876321bafac58fba862406366cb
• Referencehttps://github.com/pi-hole/pi-hole/commit/e05dc3f139206fd8d0e4a052dceefb9056533517
• Referencehttps://github.com/pi-hole/pi-hole/pull/6719
• Referencehttps://github.com/pi-hole/pi-hole/releases/tag/v6.5
• Referencehttps://github.com/pi-hole/pi-hole/security/advisories/GHSA-xch2-4qxw-g5vj