AlmaLinux 8 — libwmf — vulnerability — patch and remediation guide

📖 ~4 min read  •  Source: AlmaLinux ALSA ALSA-2019:2722

Related CVEs: CVE-2019-6978

Upstream summary: The libwmf packages provide a library for reading and converting Windows Metafile Format (WMF) vector graphics. The library is used by applications such as GIMP and ImageMagick.

Security Fix(es):

* gd: double free in the gdImage*Ptr in gd_gif_out.c, gd_jpeg.c, and gd_wbmp.c (CVE-2019-6978)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References sectio

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

Nothing executes libwmf on its own; its code runs inside whatever links against or imports it, so the exposed surface on an AlmaLinux 8 host is the union of every process that has loaded it — web workers, cron jobs, mail handlers, backup agents. The package manager replaces the files on disk, but processes already running keep the old build mapped, and virtualenvs, vendored copies and container images each carry their own copy, so a host can report itself patched while still running vulnerable code. libwmf is a library — code loaded by other programs rather than a daemon — so there is no unit to restart and systemctl status libwmf will simply report no such unit; restart its consumers instead.

Environment & Reproduction

Reproduction targets AlmaLinux 8. Confirm release and the installed package:

cat /etc/almalinux-release
cat /etc/os-release
rpm -q libwmf
dnf info libwmf | head -20

Exercise the workload that uses libwmf while collecting:

sudo needs-restarting -u  # --useronly: restrict to the invoking user's processes (useful on shared/app hosts)
sudo lsof -n +L1  # link count < 1 = file deleted but still open/mmap'd; this is the ground truth after an RPM replaces a .so (package: lsof)
sudo lsof -n +L1 2>/dev/null | awk 'NR>1 {print $1, $2}' | sort -u  # condensed COMMAND + PID list of every process still running old code
sudo journalctl -xe --no-pager | tail -200
sudo tail -200 /var/log/dnf.log
sudo tail -200 /var/log/audit/audit.log
# For an evidence bundle bundle with sosreport:
sudo sosreport --batch

Root Cause Analysis

Root cause is documented in AlmaLinux ALSA ALSA-2019:2722. AlmaLinux / Red Hat maintainers shipped fixes in the corresponding libwmf update for AlmaLinux 8; running an outdated build leaves the host exposed to the failure modes described in the advisory. Correlate dnf history with system logs:

sudo dnf history | head
sudo dnf history list libwmf
sudo dnf history info <id>
sudo ausearch -m AVC,USER_AVC -ts today | tail -100
cat /proc/sys/kernel/tainted   # non-zero = tainted kernel / out-of-tree modules

Quick Triage

Run these on AlmaLinux 8 to capture the current state of libwmf:

rpm -q libwmf                              # installed NVR
rpm -V libwmf                              # verify shipped files
sudo dnf check-update --security
sudo dnf updateinfo list cves
systemctl --failed --no-pager
sudo firewall-cmd --list-all
getenforce && sestatus
dnf repoquery -l libwmf 2>/dev/null | grep -E '/lib/systemd/system/.*\.(service|socket|timer)$'  # same check WITHOUT installing (EL7/Amazon Linux 2: yum install yum-utils, then: repoquery -l libwmf)
systemctl show --no-pager -p Type,RemainAfterExit <UNIT>  # Type=oneshot (often paired with a .timer) means a one-shot job, NOT a daemon -- do not 'restart' it, let the timer fire

Step-by-Step Diagnosis

1. List failed systemd units.

   systemctl --failed --no-pager

2. Tail the journal for libwmf and the system bus.

   sudo journalctl -xe -f --no-pager

3. Inspect firewall posture.

   sudo firewall-cmd --list-all-zones --permanent
   sudo nft list ruleset 2>/dev/null | head -50

4. Surface SELinux denials and author a local policy module if needed.

   sudo ausearch -m AVC,USER_AVC -ts today
   sudo ausearch -m AVC -ts today | audit2allow -a -M /tmp/local-fix
   sudo semodule -i /tmp/local-fix.pp

5. Verify libwmf integrity and reinstall if anything is altered.

   sudo rpm -V libwmf
   sudo dnf reinstall libwmf

6. Correlate findings with /var/log/dnf.log, dnf history, and AlmaLinux ALSA ALSA-2019:2722 to pin the change that introduced the regression.

Solution – Primary Fix

Apply the corrective dnf transaction referenced by AlmaLinux ALSA ALSA-2019:2722, then reload affected systemd units:

sudo dnf -y makecache
sudo dnf -y upgrade --security              # apply ALL security errata (recommended)
# Or target a single package:
sudo dnf -y upgrade libwmf
sudo systemctl daemon-reload
# Unit name may differ from pkg name; check first:
sudo needs-restarting -s | sort -u  # STEP 1: read the list before acting. dbus.service, systemd-logind.service and PID 1 must NOT be blind-restarted on a live host -- those mean 'reboot'
sudo systemctl daemon-reload  # STEP 3: pick up any unit files the update rewrote
sudo systemctl restart <UNIT> && sudo systemctl is-active <UNIT> && sudo systemctl status --no-pager --full <UNIT>  # single-unit path, with an immediate health check
systemctl --user list-units --type=service --no-pager  # desktop/session and per-user services are a separate manager; restart them with: systemctl --user restart <UNIT>
rpm -q libwmf                                # confirm new NVR

For kernel / glibc / systemd / openssl advisories a reboot is required (or kpatch where licensed):

sudo needs-restarting -r                    # report whether reboot needed
sudo systemctl reboot                       # or: sudo shutdown -r now
# kpatch (Red Hat / Oracle) avoids reboot for many kernel CVEs:
sudo dnf install -y kpatch kpatch-dnf
sudo dnf kpatch auto                        # enable auto-patching
sudo kpatch list

Solution – Alternative Approaches

If the primary patch is not viable, choose from these:

• Roll back the offending dnf transaction:

  sudo dnf history list | head
  sudo dnf history info <id>
  sudo dnf history undo <id>

• Version-lock the package so dnf cannot upgrade it:

  sudo dnf install -y python3-dnf-plugin-versionlock
  sudo dnf versionlock add libwmf
  sudo dnf versionlock list
  sudo dnf versionlock delete libwmf      # remove the lock

• Install an older NVR if a regression is suspected:

  dnf --showduplicates list libwmf | tac | head
  sudo dnf install -y --allowerasing libwmf-<older-NVR>

• Switch SELinux to permissive briefly to confirm policy is the cause, then re-enforce:

  sudo setenforce 0
  # reproduce, capture denials, author a custom module:
  sudo ausearch -m AVC -ts recent | audit2allow -a -M mylocal
  sudo semodule -i mylocal.pp
  sudo setenforce 1

• Take an LVM snapshot before kernel / glibc upgrades for fast rollback:

  sudo lvs
  sudo lvcreate -s -n preupgrade -L 4G /dev/<vg>/<lv>
  # revert later via:
  sudo lvconvert --merge /dev/<vg>/preupgrade && sudo systemctl reboot

• Where kpatch is licensed, apply kernel fixes without reboot:

  sudo kpatch list
  sudo kpatch load /usr/lib/modules/$(uname -r)/extra/kpatch/*.ko

Verification & Acceptance Criteria

All of these should pass after the fix:

rpm -q libwmf                                            # expected fixed NVR
sudo dnf updateinfo list cves --installed               # CVEs above no longer listed
sudo firewall-cmd --list-services
getenforce
sudo needs-restarting -r

The conditions described in the advisory must no longer be reported for libwmf across two consecutive runs.

Rollback Plan

Capture state before any change:

rpm -qa > /root/rpm-pre.txt
sudo dnf history list > /root/dnf-history-pre.txt
# Optional LVM snapshot of the root LV:
sudo lvcreate -s -n preupgrade -L 4G /dev/<vg>/<lv>

To revert if the patch is bad:

sudo dnf history undo <id>
# Or downgrade just the package:
sudo dnf install -y --allowerasing libwmf-<older-NVR>
sudo systemctl daemon-reload
# Or merge the LVM snapshot and reboot:
sudo lvconvert --merge /dev/<vg>/preupgrade && sudo systemctl reboot
# Custom SELinux policy cleanup:
sudo semodule -r mylocal

Prevention & Hardening

Reduce the chance of this recurring on AlmaLinux 8:

• Enable automatic security patching:

  sudo dnf install -y dnf-automatic
  sudo sed -i 's/^upgrade_type.*/upgrade_type = security/' /etc/dnf/automatic.conf
  sudo sed -i 's/^apply_updates.*/apply_updates = yes/' /etc/dnf/automatic.conf
  sudo systemctl enable --now dnf-automatic.timer

• Subscribe to almalinux-announce and watch Red Hat security updates for upstream changes.

• Mirror through a local Pulp / Foreman / Spacewalk-style repo for controlled rollouts:

  sudo dnf install -y dnf-utils createrepo_c
  sudo reposync --download-metadata --downloadcomps -p /srv/mirror -- repoid=baseos
  sudo createrepo_c /srv/mirror/baseos

• Version-lock sensitive packages so they cannot be auto-upgraded:

  sudo dnf install -y python3-dnf-plugin-versionlock
  sudo dnf versionlock add libwmf

• Monitor file integrity with AIDE:

  sudo dnf install -y aide
  sudo aide --init && sudo mv /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz
  sudo aide --check

• Enable kpatch so kernel CVEs can be remediated without reboot:

  sudo dnf install -y kpatch kpatch-dnf
  sudo dnf kpatch auto
  sudo kpatch list

• Keep SELinux in enforcing mode and review custom modules in /etc/selinux/targeted/ after every package upgrade.

• Apply CIS AlmaLinux 8 Benchmark hardening and remove unused packages.

Related Errors & Cross-Refs

Issues that commonly surface alongside a libwmf update: dnf lock contention, systemd unit ordering cycles, SELinux AVC bursts, firewalld zone drift, and kernel taint flags. Useful triage:

sudo dnf check
systemd-analyze critical-chain
sudo ausearch -m AVC -ts today | tail
sudo firewall-cmd --get-active-zones
cat /proc/sys/kernel/tainted
sudo needs-restarting -r

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References & Further Reading

Primary reference: AlmaLinux ALSA ALSA-2019:2722. Manual pages useful on AlmaLinux 8:

man dnf
man dnf.conf
man systemctl
man journalctl
man firewall-cmd
man semanage
man audit2allow
man kpatch
man sosreport

Other resources: wiki.almalinux.org, Red Hat CVE database, AlmaLinux errata, and per-package notes in /usr/share/doc/libwmf/ for components implicated in this advisory.

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