Alpine Linux edge — kpmcore — vulnerability — patch and remediation guide

📖 ~4 min read  •  Source: Alpine secdb entry — kpmcore 4.2.0-r0

Related CVEs: CVE-2020-27187

Upstream summary: Alpine community repository for vedge ships kpmcore 4.2.0-r0 which addresses CVE-2020-27187.

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 kpmcore on its own; its code runs inside whatever links against or imports it, so the exposed surface on an Alpine Linux edge 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. kpmcore is a library — code loaded by other programs rather than a daemon — so there is no service to restart and rc-service kpmcore will simply report no such service; restart its consumers instead.

Environment & Reproduction

Reproduction targets Alpine Linux edge. Confirm release and the installed package:

cat /etc/alpine-release
cat /etc/os-release
apk info -v kpmcore
apk policy kpmcore
apk version | grep -w kpmcore || true

Exercise the workload that uses kpmcore while collecting:

sudo tail -200 /var/log/messages       # busybox syslog / syslog-ng
sudo dmesg | tail -200
rc-service "$SVC" needsme  # HARD dependants: OpenRC will stop these, restart $SVC, then start them again - review this list before you touch anything
rc-service "$SVC" restart && rc-service "$SVC" status  # restart and confirm 'status: started' - never assume it came back
rc-service nginx reload  # WARNING - reload/HUP does NOT re-exec the binary, the old deleted library stays mapped. For a shared-library patch you MUST use 'restart', not 'reload'.
rc-service sshd restart  # safe: OpenRC restarts the listener only, established SSH sessions survive - still, keep a second session open before you run it
sudo rc-status
sudo apk audit --system

Root Cause Analysis

Root cause is recorded in Alpine secdb entry — kpmcore 4.2.0-r0. Alpine maintainers shipped the fix in 4.2.0-r0 for Alpine Linux edge; running an older build leaves the host exposed. Correlate apk transactions with the kernel ring buffer and OpenRC logs:

sudo tail -200 /var/log/apk.log
apk info -v kpmcore
apk info -L kpmcore | head
sudo dmesg --ctime | tail -100
ls -lt /var/log/rc.log 2>/dev/null && sudo tail -100 /var/log/rc.log

Quick Triage

Run these on Alpine Linux edge to capture the current state of kpmcore:

apk info -v kpmcore                       # installed version
apk policy kpmcore                        # repository / pin info
apk version -l '<'                       # all packages with newer candidates
sudo apk audit --system
apk info -L kpmcore | head                # files shipped by kpmcore
sudo rc-status                           # OpenRC runtime state
sudo rc-update show                      # services per runlevel
sudo iptables -L -n -v --line-numbers 2>/dev/null | head -40
sudo nft list ruleset 2>/dev/null | head -40
# If kpmcore ships an OpenRC service (init name may differ from pkg name,
# e.g. nginx, postgresql, php-fpm83):
ls /etc/init.d/ | grep -i kpmcore | head

Step-by-Step Diagnosis

1. List OpenRC services and any failed ones.

   sudo rc-status
   sudo rc-status --crashed

2. Inspect logs for kpmcore.

   sudo grep -i kpmcore /var/log/messages | tail -200
   sudo dmesg | tail -200

3. Inspect firewall posture (Alpine ships iptables/nftables or the awall front-end).

   sudo iptables -L -n -v --line-numbers
   sudo nft list ruleset
   sudo awall list 2>/dev/null || true

4. Verify kpmcore integrity and reinstall if files are altered.

   sudo apk verify kpmcore
   sudo apk fix kpmcore

5. Confirm the current vs. available version for kpmcore.

   apk version | grep -w kpmcore || true
   apk policy kpmcore

6. Correlate findings with /var/log/apk.log and Alpine secdb entry — kpmcore 4.2.0-r0 to pin the change that introduced the regression.

Solution – Primary Fix

Apply the corrective apk transaction referenced by Alpine secdb entry — kpmcore 4.2.0-r0, then restart affected OpenRC services:

sudo apk update
sudo apk upgrade --available --no-cache       # apply all repository updates
# Or target a single package:
sudo apk add --upgrade kpmcore
apk info -v kpmcore                              # confirm new version
sudo rc-update add kpmcore default 2>/dev/null || true

For kernel / musl / openssl updates a reboot is required (Alpine has no live-patching equivalent of kpatch):

apk info -v linux-lts linux-virt 2>/dev/null
sudo sync && sudo reboot
# On Alpine diskless / lbu installations, commit the change first:
sudo lbu status
sudo lbu commit -d

Solution – Alternative Approaches

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

• Roll back to a known-good version by installing a pinned version from /etc/apk/cache:

  ls /etc/apk/cache/ | head
  sudo apk add kpmcore=4.2.0-r0     # downgrade / pin to a specific version
  sudo apk fix

• Hold the package so apk cannot upgrade it during the next apk upgrade:

  echo 'kpmcore' | sudo tee -a /etc/apk/world
  # To pin a version, edit /etc/apk/world to read: kpmcore=4.2.0-r0
  sudo apk fix

• Pull the fix from edge while staying on a stable release (tagged repo):

  echo '@edge https://dl-cdn.alpinelinux.org/alpine/edge/main' | sudo tee -a /etc/apk/repositories
  sudo apk add kpmcore@edge

• Use awall to ring-fence the affected service while you patch:

  sudo apk add awall
  sudo awall list
  sudo awall enable <policy>
  sudo awall activate

• Take an lbu snapshot of /etc before kernel / musl upgrades (Alpine diskless mode):

  sudo lbu status
  sudo lbu package /var/backups/alpine-pre-upgrade.apkovl.tar.gz
  # Revert later by booting from media and restoring the apkovl tarball.

• For container deployments, rebuild the image from a patched base:

  docker run --rm alpine:edge apk version | grep -w kpmcore || true
  # In your Dockerfile, force a refresh: RUN apk add --no-cache --upgrade kpmcore

Verification & Acceptance Criteria

All of these should pass after the fix:

apk info -v kpmcore                              # expected fixed version
sudo apk audit --system                         # the package no longer flagged
sudo apk verify kpmcore
sudo grep -iE 'error|fail' /var/log/messages | grep -i kpmcore | tail -50 || echo OK
sudo iptables -L -n -v | head -20
sudo nft list ruleset | head -20

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

Rollback Plan

Capture state before any change:

apk info -v > /root/apk-pre.txt
sudo cp /etc/apk/world /root/world-pre
sudo cp -a /var/log/apk.log /root/apk.log-pre 2>/dev/null || true
# On lbu / diskless installs, snapshot the apkovl:
sudo lbu package /var/backups/alpine-pre-upgrade.apkovl.tar.gz

To revert if the patch is bad:

# Reinstall the previous version from /etc/apk/cache (must be mounted):
ls /etc/apk/cache/ | head
sudo apk add kpmcore=<previous-version>
# Or restore the saved apkovl on diskless:
sudo tar -xzf /var/backups/alpine-pre-upgrade.apkovl.tar.gz -C /
sudo reboot

Prevention & Hardening

Reduce the chance of this recurring on Alpine Linux edge:

• Run apk audit --system on a schedule and fail builds on new findings:

  # /etc/periodic/daily/apk-audit
  #!/bin/sh
  apk update -q && apk audit --system > /var/log/apk-audit.log

• Mount /etc/apk/cache so previous versions are always available for rollback:

  sudo mkdir -p /etc/apk/cache
  sudo setup-apkcache /etc/apk/cache

• Subscribe to alpine-security and watch security.alpinelinux.org for new CVE entries.

• Mirror the Alpine repository locally for controlled rollouts:

  sudo apk add rsync
  rsync -av --delete rsync://rsync.alpinelinux.org/alpine/v3.20/main/ /srv/mirror/v3.20/main/
  rsync -av --delete rsync://rsync.alpinelinux.org/alpine/v3.20/community/ /srv/mirror/v3.20/community/

• Pin sensitive packages in /etc/apk/world with explicit versions so apk cannot silently bump them.

• Alpine does not enable mandatory-access-control frameworks (such as AppArmor) by default; consult [grsecurity/PaX] or [seccomp profile] in container deployments and apply CIS-style hardening for Alpine Linux edge (disable unused OpenRC services, set rc_logger=YES in /etc/rc.conf, mount /tmp with nosuid,nodev).

• For container fleets, scan images in CI:

  docker run --rm alpine:edge apk version
  trivy image --severity HIGH,CRITICAL myrepo/app:tag

Related Errors & Cross-Refs

Issues that commonly surface alongside a kpmcore update: apk lock contention (/var/lib/apk/lock), OpenRC dependency cycles, busybox applet quirks vs. coreutils, and musl-vs-glibc behavioural differences. Useful triage:

sudo apk fix
sudo rc-status --crashed
ls /var/lib/apk/lock 2>/dev/null
sudo grep -i busybox /var/log/messages | tail
cat /proc/sys/kernel/tainted

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References & Further Reading

Primary reference: Alpine secdb entry — kpmcore 4.2.0-r0. Manual pages useful on Alpine Linux edge:

apk --help
man apk
man rc-service
man rc-update
man rc-status
man iptables
man nft
man awall
man lbu

Other resources: wiki.alpinelinux.org, security.alpinelinux.org, pkgs.alpinelinux.org, and per-package notes in /usr/share/doc/kpmcore/ for components implicated in this advisory.

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