FreeBSD 13 — ruby22-gems — multiple vulnerabilities (2 CVEs) — patch and remediation guide

📖 ~4 min read  •  Source: FreeBSD VuXML

VuXML topic: rubygems — deserialization vulnerability

Related CVEs: CVE-2015-3900 CVE-2017-0903

Upstream summary: oss-security mailing list: There is a possible unsafe object desrialization vulnerability in RubyGems. It is possible for YAML deserialization of gem specifications to bypass class white lists. Specially crafted serialized objects can possibly be used to escalate to remote code execution.

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

ruby22-gems on FreeBSD 13 runs only when something invokes it, so there is no crash loop and no failed unit to notice — the exposure is input-driven. A developer build, a CI job, a package rebuild or triage tooling that runs objdump, readelf or gdb across an untrusted binary can hit a malformed section header and corrupt memory inside the toolchain process, running code as the build user. On a shared builder or CI runner that means tampered build output rather than downtime. ruby22-gems is a build-time developer tool that exits when the command finishes, so there is no service to restart — only in-flight builds and long-lived helpers such as distcc or clangd still hold the old binaries.

Environment & Reproduction

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

freebsd-version -kru
uname -a
pkg info ruby22-gems
pkg query "%n-%v" ruby22-gems
pkg audit -F
service -e

Exercise the workload that uses ruby22-gems 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 The FreeBSD ports security team shipped a corrective ruby22-gems port revision; hosts on an outdated build remain exposed.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 ruby22-gems:

pkg version -v ruby22-gems                # installed vs available version
pkg audit ruby22-gems                     # 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
# e.g. bind918→named, php83→php-fpm), check it:
pkg query '%Fp' ruby22-gems | sed -n 's|.*/etc/rc\.d/||p'  # FreeBSD: the REAL service name(s) = basename of the rc.d script (bind918 -> named, postgresql16-server -> postgresql, apache24 -> apache24)
pkg query '%b' ruby22-gems  # FreeBSD: shared libraries PROVIDED by ruby22-gems. Non-empty here + no rc.d script = it is a library: patch it, then restart its consumers

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 ruby22-gems.

   pkg check -B ruby22-gems
   pkg check -d ruby22-gems    # verify shared-library deps

5. Reinstall ruby22-gems if integrity check fails.

   pkg install -fy ruby22-gems

6. Correlate findings with /var/log/pkg.log and FreeBSD VuXML to pin the commit that introduced the regression.

Solution – Primary Fix

Install the corrective ruby22-gems port revision referenced by FreeBSD VuXML:

sudo pkg update
sudo pkg upgrade ruby22-gems              # or: sudo pkg upgrade -y for the whole system
pkg audit ruby22-gems                    # 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>/ruby22-gems
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 ruby22-gems

• 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 ruby22-gems
  pkg rquery -r FreeBSD-quarterly '%n-%v' ruby22-gems
  # 2. Install from a specific saved .pkg file:
  sudo pkg add -f /path/to/ruby22-gems-<older-version>.pkg
  # 3. Or switch the host repo to the quarterly branch (see snippet below) and:
  sudo pkg upgrade -fr FreeBSD-quarterly ruby22-gems

• 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 ruby22-gems-jail -r 13.4-RELEASE
  iocage set allow_raw_sockets=0 ruby22-gems-jail
  # or with Bastille:
  bastille create ruby22-gems-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 ruby22-gems                # shows the expected fixed version
pkg audit ruby22-gems               # no advisory for this package (exit code 0)
tail -50 /var/log/messages   # no new errors after upgrade
# If ruby22-gems ships a service, confirm it is running under its rc.d name:

The conditions described in the advisory must no longer be reported for ruby22-gems 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-ruby22-gems-patch

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

sudo pkg add -f /var/cache/pkg/ruby22-gems-<previous-version>.pkg
# Or activate the pre-patch boot environment and reboot (ZFS-on-root only):
sudo bectl activate pre-ruby22-gems-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 ruby22-gems:

• 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>/ruby22-gems

• Version-pin sensitive packages:

  sudo pkg lock ruby22-gems

• 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:

  ruby22-gems_jail {
    allow.raw_sockets = 0;
    allow.sysvipc    = 0;
    allow.mount      = 0;
    allow.chflags    = 0;
  }

Related Errors & Cross-Refs

Issues that commonly surface alongside a ruby22-gems update: 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 this advisory.