Amazon Linux 2023 — cifs-utils — multiple vulnerabilities (3 CVEs) — patch and remediation guide

📖 ~4 min read  •  Source: Amazon Linux advisory ALAS2023-2024-530

Related CVEs: CVE-2022-27239 CVE-2022-29869 CVE-2025-2312

Upstream summary: A stack-based buffer overflow issue was found in pifs-utils. Parsing the mount.cifs ip command-line argument can lead to local attackers gaining root privileges. (CVE-2022-27239) A flaw was found in cifs-utils. When verbose logging is enabled, invalid credentials file lines may be dumped to stderr. This may lead to information disclosure in particular conditions when the credentials file given is sensitive and contains = signs. (CVE-2022-29869)

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 visibly changes on an Amazon Linux 2023 host until cifs-utils is next invoked: it runs, exits and leaves no daemon behind, so there is no restart loop or service log to watch. Exposure is per-invocation, and the invocations that matter are the unattended ones — cron jobs, backup and deployment scripts, CI runners, and anything passing attacker-influenced input such as a remote URL, a supplied archive or an untrusted filename. Where cifs-utils is run under sudo or from a privileged job, the same flaw becomes local privilege escalation. cifs-utils ships command-line programs that run when invoked and then exit, so there is no unit to restart — systemctl and journalctl -u have nothing to act on; only the next invocation matters.

Environment & Reproduction

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

cat /etc/system-release
cat /etc/os-release
rpm -q cifs-utils
dnf info cifs-utils | head -20

Exercise the workload that uses cifs-utils while collecting:

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 ALAS2023-2024-530. The Amazon Linux Security Team shipped fixes in the corresponding cifs-utils 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 cifs-utils
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 cifs-utils:

rpm -q cifs-utils                              # installed NVR
rpm -V cifs-utils                              # 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
dnf repoquery -l cifs-utils 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 cifs-utils)
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 cifs-utils and the system bus.

   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 cifs-utils integrity and reinstall if anything is altered.

   sudo rpm -V cifs-utils
   sudo dnf reinstall -y cifs-utils

6. Correlate findings with /var/log/dnf.log, dnf history, Amazon Inspector findings, and Amazon Linux advisory ALAS2023-2024-530 to pin the change that introduced the regression.

Solution – Primary Fix

Apply the corrective dnf transaction referenced by Amazon Linux advisory ALAS2023-2024-530, 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 cifs-utils
# Unit name may differ from pkg name; check first:
rpm -q cifs-utils                                # confirm new NVR

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 cifs-utils
  sudo dnf versionlock list
  sudo dnf versionlock delete cifs-utils      # remove the lock

• Install an older NVR if a regression is suspected:

  dnf --showduplicates list cifs-utils | tac | head
  sudo dnf install -y --allowerasing cifs-utils-<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=ALAS2023-2024-530 kernel

Verification & Acceptance Criteria

All of these should pass after the fix:

rpm -q cifs-utils                                            # expected fixed NVR
sudo dnf updateinfo list cves --installed              # CVEs above no longer listed
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-2022-27239}'

The conditions described in the advisory must no longer be reported for cifs-utils 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 cifs-utils-<older-NVR>
# 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 cifs-utils

• 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 a cifs-utils update: 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 ALAS2023-2024-530. 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/cifs-utils/ for components implicated in this advisory.

View all Amazon Linux 2023 tutorials on the Tutorials Hub →