FreeBSD 13 — ap20-mod_pubcookie — security advisory — patch and remediation guide

📖 ~4 min read  •  Source: FreeBSD VuXML

VuXML topic: mod_pubcookie — Empty Authentication Security Advisory

Upstream summary: Nathan Dors, Pubcookie Project reports: An Abuse of Functionality vulnerability in the Pubcookie authentication process was found. This vulnerability allows an attacker to appear as if he or she were authenticated using an empty userid when such a userid isn't expected. Unauthorized access to web content and applications may result where access is restricted to users who can authenticate successfully but where no additional authorization is performed after authentication.

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

On FreeBSD 13 hosts that have ap20-mod_pubcookie installed, operators see behaviour consistent with the FreeBSD VuXML entry: pkg audit flags the installed version; any daemon, CLI tool, or application linked against ap20-mod_pubcookie may misbehave or fail to start after upgrade; and — for security-rated advisories — the host is exposed to the vulnerabilities above. Impact ranges from a single restart cycle to full availability incidents on jails, bhyve guests, or downstream consumers that depend on ap20-mod_pubcookie.

Environment & Reproduction

Reproduction targets FreeBSD 13. Confirm release, installed package, and capture baseline state:

freebsd-version -kru
uname -a
pkg info ap20-mod_pubcookie
pkg query "%n-%v" ap20-mod_pubcookie
pkg audit -F
service -e

Trigger the workflow that exposes ap20-mod_pubcookie — security advisory — patch and remediation guide while collecting:

tail -200 /var/log/messages
dmesg -a | tail -200
tail -200 /var/log/pkg.log

Root Cause Analysis

Root cause is tracked at FreeBSD VuXML. The FreeBSD ports security team shipped a corrective ap20-mod_pubcookie port revision; hosts on an outdated build remain exposed. Correlate package logs with system logs and kernel state to isolate the change that triggered the failure mode:

tail -500 /var/log/pkg.log
tail -500 /var/log/messages
sysctl kern.lastpid
sysctl kern.osreldate     # numeric __FreeBSD_version, e.g. 1400097

Quick Triage

Run these checks on FreeBSD 13 to confirm the failure mode and current state of ap20-mod_pubcookie:

pkg version -v ap20-mod_pubcookie                # installed vs available version
pkg audit ap20-mod_pubcookie                     # advisory match for this package
tail -100 /var/log/messages
dmesg -a | tail -100
kldstat                              # kernel module state (for kernel/driver pkgs)
pfctl -sr 2>/dev/null || ipfw list   # only if pf/ipfw is enabled
# If ap20-mod_pubcookie ships an rc.d service (script name may differ from the pkg name,
# e.g. bind918→named, php83→php-fpm), check it:
service -e | grep -i ap20-mod_pubcookie && service <rc-script-name> status

Step-by-Step Diagnosis

1. List enabled services (only relevant if the package provides one).

   service -e

2. Follow live logs.

   tail -F /var/log/messages
   dmesg

3. Validate firewall rules (skip if neither pf nor ipfw is enabled).

   pfctl -sr -v 2>/dev/null || ipfw show

4. Check package integrity for ap20-mod_pubcookie.

   pkg check -B ap20-mod_pubcookie
   pkg check -d ap20-mod_pubcookie    # verify shared-library deps

5. Reinstall ap20-mod_pubcookie if integrity check fails.

   pkg install -fy ap20-mod_pubcookie

6. Correlate findings with /var/log/pkg.log and FreeBSD VuXML to pin the commit that introduced ap20-mod_pubcookie — security advisory — patch and remediation guide.

Solution – Primary Fix

Install the corrective ap20-mod_pubcookie port revision referenced by FreeBSD VuXML:

sudo pkg update
sudo pkg upgrade ap20-mod_pubcookie              # or: sudo pkg upgrade -y for the whole system
# If ap20-mod_pubcookie provides an rc.d service, restart it (script name may differ from pkg name):
# sudo service <rc-script-name> restart
pkg audit ap20-mod_pubcookie                    # confirm no remaining advisory for this package

For ports-tree builders (FreeBSD 13.x and earlier used portsnap; on FreeBSD 14+ the ports tree is fetched with Git):

# FreeBSD 14+ (portsnap was removed):
sudo pkg install -y git-lite
sudo git clone --depth 1 https://git.FreeBSD.org/ports.git /usr/ports
# FreeBSD 13.x and earlier:
# sudo portsnap fetch update
cd /usr/ports/<category>/ap20-mod_pubcookie
sudo make deinstall reinstall clean

Reboot only if the package ships a kernel module or replaces a shared library used by long-running daemons.

Solution – Alternative Approaches

If the primary fix is not viable, choose from these alternatives:

• Lock the package until the fix is vetted:

  sudo pkg lock ap20-mod_pubcookie

• Downgrade to a known-good revision. pkg install pkgname-VERSION is not a real downgrade syntax — fetch a specific build instead:

  # 1. Discover available versions across configured repos:
  pkg search -e ap20-mod_pubcookie
  pkg rquery -r FreeBSD-quarterly '%n-%v' ap20-mod_pubcookie
  # 2. Install from a specific saved .pkg file:
  sudo pkg add -f /path/to/ap20-mod_pubcookie-<older-version>.pkg
  # 3. Or switch the host repo to the quarterly branch (see snippet below) and:
  sudo pkg upgrade -fr FreeBSD-quarterly ap20-mod_pubcookie

• Switch the pkg repository between quarterly and latest by editing /usr/local/etc/pkg/repos/FreeBSD.conf:

  FreeBSD: {
    url: "pkg+https://pkg.FreeBSD.org/${ABI}/quarterly",
    mirror_type: "srv",
    signature_type: "fingerprints",
    fingerprints: "/usr/share/keys/pkg",
    enabled: yes
  }

• Isolate the affected service in a jail with stricter firewall rules:

  iocage create -n ap20-mod_pubcookie-jail -r 13.4-RELEASE
  iocage set allow_raw_sockets=0 ap20-mod_pubcookie-jail
  # or with Bastille:
  bastille create ap20-mod_pubcookie-jail 13.4-RELEASE 10.0.0.10

• Replace the service with a vendored static build for the period between exposure detection and full rollout.

Verification & Acceptance Criteria

All of these should pass after the fix:

pkg info ap20-mod_pubcookie                # shows the expected fixed version
pkg audit ap20-mod_pubcookie               # no advisory for this package (exit code 0)
tail -50 /var/log/messages   # no new errors after upgrade
# If ap20-mod_pubcookie ships a service, confirm it is running under its rc.d name:
# service <rc-script-name> status

The original reproduction for ap20-mod_pubcookie — security advisory — patch and remediation guide must not trigger across two consecutive runs.

Rollback Plan

Capture state before any change (only ZFS root has boot environments — UFS hosts skip bectl):

pkg query "%n-%v" > /root/pkg-pre.txt
# ZFS-on-root only:
sudo bectl create pre-ap20-mod_pubcookie-patch

To revert if the upgrade is bad, reinstall the previously saved .pkg file:

sudo pkg add -f /var/cache/pkg/ap20-mod_pubcookie-<previous-version>.pkg
# Or activate the pre-patch boot environment and reboot (ZFS-on-root only):
sudo bectl activate pre-ap20-mod_pubcookie-patch
sudo shutdown -r now

For kernel/loader changes on a UFS host, boot the previous kernel from the loader prompt (press 3 at the menu, then boot kernel.old).

Prevention & Hardening

Prevent recurrence on FreeBSD 13 hosts running ap20-mod_pubcookie:

• Enable the daily security pkg audit in /etc/periodic.conf:

  daily_status_security_pkgaudit_enable="YES"

• Subscribe to freebsd-security-notifications at lists.freebsd.org.

• Mirror through a local pkg repository managed by poudriere:

  poudriere jail -c -j 13amd64 -v 13.4-RELEASE
  poudriere ports -c -p default
  poudriere bulk -j 13amd64 -p default <category>/ap20-mod_pubcookie

• Version-pin sensitive packages:

  sudo pkg lock ap20-mod_pubcookie

• Take an automatic ZFS boot-environment snapshot before every upgrade (ZFS root only):

  sudo bectl create pre-upgrade-$(date +%Y%m%d)

• Monitor file integrity (create a baseline, verify against it later):

  # Create a baseline (use -c; target /usr/local/etc, /etc, /boot — NOT /):
  sudo mtree -c -K sha256digest -p /usr/local/etc > /var/db/usr-local-etc.mtree
  sudo mtree -c -K sha256digest -p /etc          > /var/db/etc.mtree
  # Verify later:
  sudo mtree -p /usr/local/etc < /var/db/usr-local-etc.mtree
  # Or with AIDE for a richer ruleset:
  sudo pkg install -y aide && sudo aide --init && sudo aide --check

• Harden jails with allow.* tunables in /etc/jail.conf:

  ap20-mod_pubcookie_jail {
    allow.raw_sockets = 0;
    allow.sysvipc    = 0;
    allow.mount      = 0;
    allow.chflags    = 0;
  }

Related Errors & Cross-Refs

Issues that commonly surface alongside ap20-mod_pubcookie — security advisory — patch and remediation guide: pkg lock contention, mismatched ABI after kernel/userland skew, pf rule drift, and stale shared-library references after upgrade. Triage with:

freebsd-version -kru
uname -K
pkg check -d
pfctl -sr

View all freebsd-13 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Primary reference: FreeBSD VuXML. Useful manual pages on FreeBSD 13:

man pkg
man freebsd-update
man pfctl
man ipfw
man bectl
man periodic.conf

Other resources: the FreeBSD Handbook, the FreeBSD Security Advisories at security.freebsd.org, and the /usr/ports/UPDATING file for port-specific notes implicated in ap20-mod_pubcookie — security advisory — patch and remediation guide.