Rocky Linux 8 — perl-File-Which — vulnerability — patch and remediation guide

📖 ~4 min read  •  Source: Rocky Linux RXSA RLSA-2026:8096

Related CVEs: CVE-2025-40909

Upstream summary: Perl is a high-level programming language that is commonly used for system administration utilities and web programming.

Security Fix(es):

* perl: Perl threads have a working directory race condition where file operations may target unintended paths (CVE-2025-40909)

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 section.

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 Rocky Linux 8 hosts that have perl-File-Which installed, operators report behaviour consistent with Rocky Linux RXSA RLSA-2026:8096: dnf refuses to install or restart affected services, SELinux AVC denials appear in /var/log/audit/audit.log, and — for security-rated advisories — the host is exposed to the vulnerability set above. Impact ranges from a single service-restart loop to wider availability incidents whenever perl-File-Which sits on the serving path.

Environment & Reproduction

Reproduction targets Rocky Linux 8. Confirm release and the installed package:

cat /etc/rocky-release
cat /etc/os-release
rpm -q perl-File-Which
dnf info perl-File-Which | head -20

Trigger the workflow that exposes perl-File-Which — vulnerability — patch and remediation guide while collecting:

sudo journalctl -u perl-File-Which -b --no-pager | tail -200
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 Rocky Linux RXSA RLSA-2026:8096. Rocky Linux / Red Hat maintainers shipped fixes in the corresponding perl-File-Which update for Rocky Linux 8; running an outdated build leaves the host exposed to the failure modes described in the advisory.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 perl-File-Which
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 Rocky Linux 8 to capture the current state of perl-File-Which:

rpm -q perl-File-Which                              # installed NVR
rpm -V perl-File-Which                              # verify shipped files
sudo dnf check-update --security
sudo dnf updateinfo list cves
systemctl --failed --no-pager
sudo firewall-cmd --list-all
getenforce && sestatus
# If perl-File-Which ships a systemd unit (unit name may differ from pkg name, e.g.
# bind→named, postgresql-server→postgresql, php-fpm→php-fpm):
systemctl list-unit-files | grep -i perl | head

Step-by-Step Diagnosis

1. List failed systemd units.

   systemctl --failed --no-pager

2. Tail the journal for perl-File-Which and the system bus.

   sudo journalctl -u perl-File-Which -f --no-pager
   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 perl-File-Which integrity and reinstall if anything is altered.

   sudo rpm -V perl-File-Which
   sudo dnf reinstall perl-File-Which

6. Correlate findings with /var/log/dnf.log, dnf history, and Rocky Linux RXSA RLSA-2026:8096 to pin the change that introduced perl-File-Which — vulnerability — patch and remediation guide.

Solution – Primary Fix

Apply the corrective dnf transaction referenced by Rocky Linux RXSA RLSA-2026:8096, 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 perl-File-Which
sudo systemctl daemon-reload
# Unit name may differ from pkg name; check first:
systemctl list-unit-files | grep -i perl | head
sudo systemctl restart perl-File-Which
rpm -q perl-File-Which                                # confirm new NVR
systemctl is-active perl-File-Which 2>/dev/null       # confirm running (if a unit exists)

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 perl-File-Which
  sudo dnf versionlock list
  sudo dnf versionlock delete perl-File-Which      # remove the lock

• Install an older NVR if a regression is suspected:

  dnf --showduplicates list perl-File-Which | tac | head
  sudo dnf install -y --allowerasing perl-File-Which-<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 perl-File-Which                                            # expected fixed NVR
sudo dnf updateinfo list cves --installed               # CVEs above no longer listed
systemctl is-active perl-File-Which 2>/dev/null
sudo journalctl -u perl-File-Which --since "5 minutes ago" --no-pager | grep -iE "error|fail" || echo OK
sudo firewall-cmd --list-services
getenforce
sudo needs-restarting -r

The original reproduction for perl-File-Which — vulnerability — patch and remediation guide must not trigger 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 perl-File-Which-<older-NVR>
sudo systemctl daemon-reload
sudo systemctl restart perl-File-Which
# 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 Rocky Linux 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 rocky-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 perl-File-Which

• 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 Rocky Linux 8 Benchmark hardening and remove unused packages.

Related Errors & Cross-Refs

Issues that commonly surface alongside perl-File-Which — vulnerability — patch and remediation guide: 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: Rocky Linux RXSA RLSA-2026:8096. Manual pages useful on Rocky Linux 8:

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

Other resources: docs.rockylinux.org, Red Hat CVE database, Rocky Linux errata, and per-package notes in /usr/share/doc/perl-File-Which/ for components implicated in perl-File-Which — vulnerability — patch and remediation guide.

View all Rocky Linux 8 tutorials on the Tutorials Hub →