Amazon Linux 2023 — kernel6.18 — multiple vulnerabilities (20 CVEs) — patch and remediation guide

📖 ~4 min read  •  Source: Amazon Linux advisory ALAS2023-2026-1709

Related CVEs: CVE-2026-46300 CVE-2025-71239 CVE-2025-71265 CVE-2025-71266 CVE-2025-71267 CVE-2025-71295 CVE-2025-71298 CVE-2025-71301  +12 more

Upstream summary: In the Linux kernel, the following vulnerability has been resolved: net: skbuff: propagate shared-frag marker through pskb_copy() (CVE-2026-46300)

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 Amazon Linux 2023 hosts that have kernel6.18 installed, operators report behaviour consistent with Amazon Linux advisory ALAS2023-2026-1709: 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 on a single EC2 instance to wider availability incidents whenever kernel6.18 sits on the serving path of an Auto Scaling group or ECS task.

Environment & Reproduction

Reproduction targets Amazon Linux 2023. Confirm release and the installed package:

cat /etc/system-release
cat /etc/os-release
rpm -q kernel6.18
dnf info kernel6.18 | head -20

Trigger the workflow that exposes kernel6.18 — multiple vulnerabilities (20 CVEs) — patch and remediation guide while collecting:

sudo journalctl -u kernel6.18 -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 (Amazon Linux ships it):
sudo sosreport --batch

For fleet-wide visibility, query Amazon Inspector and SSM at the same time:

aws inspector2 list-findings 
  --filter-criteria 'awsAccountId={comparison=EQUALS,value=<account-id>}' 
  --max-results 50
aws ssm describe-instance-patches --instance-id <i-xxxx> | head -40

Root Cause Analysis

Root cause is documented in Amazon Linux advisory ALAS2023-2026-1709. The Amazon Linux Security Team shipped fixes in the corresponding kernel6.18 update for Amazon Linux 2023; running an outdated AMI or unpatched instance leaves the host exposed to the failure modes described in the advisory.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 kernel6.18
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 Amazon Linux 2023 to capture the current state of kernel6.18:

rpm -q kernel6.18                              # installed NVR
rpm -V kernel6.18                              # verify shipped files
sudo dnf check-update --security
sudo dnf updateinfo list cves
systemctl --failed --no-pager
sudo firewall-cmd --list-all 2>/dev/null || sudo iptables -L -n
getenforce && sestatus
# If kernel6.18 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 kernel6.18 | head

Step-by-Step Diagnosis

1. List failed systemd units.

   systemctl --failed --no-pager

2. Tail the journal for kernel6.18 and the system bus.

   sudo journalctl -u kernel6.18 -f --no-pager
   sudo journalctl -xe -f --no-pager

3. Inspect firewall / security-group posture from inside the instance.

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

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 kernel6.18 integrity and reinstall if anything is altered.

   sudo rpm -V kernel6.18
   sudo dnf reinstall -y kernel6.18

6. Correlate findings with /var/log/dnf.log, dnf history, Amazon Inspector findings, and Amazon Linux advisory ALAS2023-2026-1709 to pin the change that introduced kernel6.18 — multiple vulnerabilities (20 CVEs) — patch and remediation guide.

Solution – Primary Fix

Apply the corrective dnf transaction referenced by Amazon Linux advisory ALAS2023-2026-1709, then reload affected systemd units:

sudo dnf -y makecache
sudo dnf -y update --security              # apply ALL security errata (recommended)
# Or target a single package:
sudo dnf -y update kernel6.18
sudo systemctl daemon-reload
# Unit name may differ from pkg name; check first:
systemctl list-unit-files | grep -i kernel6.18 | head
sudo systemctl restart kernel6.18
rpm -q kernel6.18                                # confirm new NVR
systemctl is-active kernel6.18 2>/dev/null       # confirm running (if a unit exists)

For kernel / glibc / systemd / openssl advisories a reboot is required (or Live Patching where available):

sudo needs-restarting -r                    # report whether reboot needed
sudo systemctl reboot                       # or: sudo shutdown -r now
# Amazon Linux Live Patching for the kernel (when enabled on the instance):
sudo dnf install -y kernel-livepatch
sudo dnf kernel-livepatch enable           # AL2 / AL2023
sudo dnf kernel-livepatch status

Roll the same change across an Auto Scaling group / fleet with AWS Systems Manager Patch Manager:

aws ssm send-command 
  --document-name AWS-RunPatchBaseline 
  --targets Key=tag:Patch,Values=yes 
  --parameters 'Operation=Install,RebootOption=RebootIfNeeded' 
  --comment 'Apply Amazon Linux security errata'
aws ssm list-command-invocations --details --max-results 5
# Confirm the patch landed across the fleet:
aws ssm describe-instance-patch-states-for-patch-group 
  --patch-group <patch-group>

For immutable infrastructure, rebuild the golden AMI in EC2 Image Builder so newly launched instances start patched (do not rely on in-place patching alone):

aws imagebuilder start-image-pipeline-execution 
  --image-pipeline-arn arn:aws:imagebuilder:<region>:<acct>:image-pipeline/<name>
aws imagebuilder list-images --owner Self --max-results 5
# Then update the launch template / ASG to the new AMI:
aws ec2 create-launch-template-version --launch-template-id <lt-id> 
  --source-version '$Latest' --launch-template-data 'ImageId=<new-ami-id>'

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 kernel6.18
  sudo dnf versionlock list
  sudo dnf versionlock delete kernel6.18      # remove the lock

• Install an older NVR if a regression is suspected:

  dnf --showduplicates list kernel6.18 | tac | head
  sudo dnf install -y --allowerasing kernel6.18-<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 EBS snapshot of the root volume before kernel / glibc upgrades for fast rollback:

  INSTANCE_ID=$(curl -s http://169.254.169.254/latest/meta-data/instance-id)
  VOL_ID=$(aws ec2 describe-instances --instance-ids $INSTANCE_ID 
    --query 'Reservations[].Instances[].BlockDeviceMappings[?DeviceName==`/dev/xvda`].Ebs.VolumeId' 
    --output text)
  aws ec2 create-snapshot --volume-id $VOL_ID 
    --description 'pre-patch-snapshot' --tag-specifications 
    'ResourceType=snapshot,Tags=[{Key=Name,Value=pre-patch}]'

• For immutable workloads, swap the ASG to a previous AMI version instead of patching in place:

  aws ec2 describe-launch-template-versions --launch-template-id <lt-id> --max-results 5
  aws autoscaling update-auto-scaling-group --auto-scaling-group-name <asg> 
    --launch-template LaunchTemplateId=<lt-id>,Version='<prev-version>'
  aws autoscaling start-instance-refresh --auto-scaling-group-name <asg>

• Where Kernel Live Patching is enabled, apply kernel fixes without reboot:

  sudo dnf kernel-livepatch status
  sudo dnf kernel-livepatch enable
  sudo dnf update -y --advisory=ALAS2023-2026-1709 kernel

Verification & Acceptance Criteria

All of these should pass after the fix:

rpm -q kernel6.18                                            # expected fixed NVR
sudo dnf updateinfo list cves --installed              # CVEs above no longer listed
systemctl is-active kernel6.18 2>/dev/null
sudo journalctl -u kernel6.18 --since "5 minutes ago" --no-pager | grep -iE "error|fail" || echo OK
sudo firewall-cmd --list-services 2>/dev/null || sudo iptables -L -n
getenforce
sudo needs-restarting -r
# Inspector should drop the finding within ~24h:
aws inspector2 list-findings 
  --filter-criteria 'vulnerabilityId={comparison=EQUALS,value=CVE-2026-46300}'

The original reproduction for kernel6.18 — multiple vulnerabilities (20 CVEs) — 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 pre-patch EBS snapshot of the root volume (run from inside the instance):
INSTANCE_ID=$(curl -s http://169.254.169.254/latest/meta-data/instance-id)
aws ec2 create-snapshot --volume-id <vol-id> --description 'pre-patch'

To revert if the patch is bad:

sudo dnf history undo <id>
# Or downgrade just the package:
sudo dnf install -y --allowerasing kernel6.18-<older-NVR>
sudo systemctl daemon-reload
sudo systemctl restart kernel6.18
# Or replace the instance from a snapshot/older AMI via ASG instance refresh:
aws autoscaling start-instance-refresh --auto-scaling-group-name <asg>
# Custom SELinux policy cleanup:
sudo semodule -r mylocal

Prevention & Hardening

Reduce the chance of this recurring on Amazon Linux 2023:

• Enable automatic security patching on each instance:

  sudo dnf install -y dnf-automatic
  sudo sed -i 's/^update_cmd.*/update_cmd = security/' /etc/dnf-automatic/dnf-automatic.conf 2>/dev/null || true
  sudo sed -i 's/^upgrade_type.*/upgrade_type = security/' /etc/dnf/automatic.conf 2>/dev/null || true
  sudo sed -i 's/^apply_updates.*/apply_updates = yes/' /etc/dnf/automatic.conf 2>/dev/null || true
  sudo systemctl enable --now dnf-automatic.timer

• Drive fleet-wide patching through AWS Systems Manager Patch Manager (preferred for any fleet bigger than a handful of instances):

  aws ssm send-command --document-name AWS-RunPatchBaseline 
    --targets Key=tag:Patch,Values=yes 
    --parameters 'Operation=Install,RebootOption=RebootIfNeeded'
  aws ssm describe-patch-baselines --filters Key=OWNER,Values=AWS
  aws ssm get-default-patch-baseline --operating-system AMAZON_LINUX_2023

• Enable Amazon Inspector for continuous CVE / package vulnerability scanning:

  aws inspector2 enable --resource-types EC2 ECR LAMBDA
  aws inspector2 list-findings 
    --filter-criteria 'severity={comparison=EQUALS,value=HIGH}' --max-results 20
  aws inspector2 batch-get-account-status

• Bake patched golden AMIs with EC2 Image Builder and roll them via ASG instance refresh instead of in-place patching for immutable infrastructure:

  aws imagebuilder list-image-pipelines
  aws imagebuilder start-image-pipeline-execution 
    --image-pipeline-arn arn:aws:imagebuilder:<region>:<acct>:image-pipeline/<name>
  aws autoscaling start-instance-refresh --auto-scaling-group-name <asg>

• Subscribe to alas.aws.amazon.com and watch AWS security bulletins for upstream changes.

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

  sudo dnf install -y python3-dnf-plugin-versionlock
  sudo dnf versionlock add kernel6.18

• 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 Kernel Live Patching so kernel CVEs can be remediated without reboot:

  sudo dnf install -y kernel-livepatch
  sudo dnf kernel-livepatch enable
  sudo dnf kernel-livepatch status

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

• Apply CIS Amazon Linux 2023 Benchmark hardening and remove unused packages.

Related Errors & Cross-Refs

Issues that commonly surface alongside kernel6.18 — multiple vulnerabilities (20 CVEs) — patch and remediation guide: dnf lock contention, systemd unit ordering cycles, SELinux AVC bursts, security-group / NACL drift, and kernel taint flags after out-of-tree modules. Useful triage:

sudo dnf check
systemd-analyze critical-chain
sudo ausearch -m AVC -ts today | tail
sudo firewall-cmd --get-active-zones 2>/dev/null || sudo iptables -L -n
cat /proc/sys/kernel/tainted
sudo needs-restarting -r
aws ssm describe-instance-patches --instance-id <i-xxxx> | tail -40

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References & Further Reading

Primary reference: Amazon Linux advisory ALAS2023-2026-1709. Manual pages useful on Amazon Linux 2023:

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

Other resources: alas.aws.amazon.com, SSM Patch Manager docs, Amazon Inspector docs, EC2 Image Builder docs, and per-package notes in /usr/share/doc/kernel6.18/ for components implicated in kernel6.18 — multiple vulnerabilities (20 CVEs) — patch and remediation guide.

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