1. Introduction
The Amazon Linux AMI : containerd vulnerability (ALAS-2020-1455) is a missing security update affecting containerized environments running on Amazon Linux AMIs. This allows malicious containers to potentially run processes with elevated privileges, impacting the confidentiality, integrity and availability of the host system. Systems using containerd are usually affected.
2. Technical Explanation
The vulnerability occurs because access controls for the shim’s API socket do not sufficiently restrict access. Specifically, the connecting process is verified to have an effective UID of 0 but other restrictions are missing. This allows containers running in the same network namespace with a reduced privilege level (but still having UID 0) to execute processes with elevated privileges on the host system. The vulnerability is referenced as CVE-2020-15257. An attacker could exploit this by creating a malicious container that leverages the unrestricted API socket access to gain higher permissions than intended.
- Root cause: Insufficient restriction of access to the shim’s abstract Unix domain socket.
- Exploit mechanism: A malicious container running with an effective UID of 0 can exploit the lack of restrictions on the shim’s API socket to run processes with elevated privileges.
- Scope: Amazon Linux AMIs using containerd are affected.
3. Detection and Assessment
To confirm if a system is vulnerable, check the installed version of containerd. A thorough method involves reviewing the ALAS advisory for specific impacted versions.
- Quick checks: Use the following command to determine the containerd version:
containerd --version - Scanning: Nessus vulnerability ID 1608925 can be used as an example, but relies on self-reported version numbers.
- Logs and evidence: Review system logs for unusual process execution or container activity. Specific log files may vary depending on the AMI configuration.
containerd --version4. Solution / Remediation Steps
4.1 Preparation
- Ensure you have sufficient disk space for the update process and a rollback plan in case of issues.
- A change window may be required depending on your environment, with approval from relevant stakeholders.
4.2 Implementation
- Step 1: Update the system using yum:
sudo yum update containerd - Step 2: Reboot the instance if prompted by the update process.
4.3 Config or Code Example
Before
# No specific configuration example available, as this is a missing update. Check containerd version.After
containerd --version # Verify updated version after applying the yum update. Expected output should show a newer version than previously installed.4.4 Security Practices Relevant to This Vulnerability
- Practice 1: Least privilege – running containers with minimal necessary permissions reduces the impact if exploited.
- Practice 2: Patch cadence – regularly applying security updates ensures systems are protected against known vulnerabilities.
4.5 Automation (Optional)
#!/bin/bash
# Example automation using yum to update containerd on multiple instances
for instance_id in $(aws ec2 describe-instances --query 'Reservations[*].Instances[*].InstanceId' --output text)
do
echo "Updating containerd on instance $instance_id..."
ssh -i /path/to/your/key.pem ec2-user@$instance_id "sudo yum update containerd -y"
done
5. Verification / Validation
Confirm the fix by verifying the updated version of containerd and performing a smoke test to ensure container functionality remains intact.
- Post-fix check: Run
containerd --versionand confirm that the output shows an updated version number. - Re-test: Re-run the initial vulnerability check (
containerd --version) to verify the issue is resolved. - Smoke test: Start a simple container (e.g.,
docker run hello-worldor equivalent) to confirm basic container functionality.
containerd --version # Expected output should show a newer version number.6. Preventive Measures and Monitoring
- Baselines: Update your security baseline or policy to include regular patching of containerd and other container-related components.
- Asset and patch process: Implement a consistent patch management cycle for all systems, including Amazon Linux AMIs.
7. Risks, Side Effects, and Roll Back
- Risk or side effect 1: The update may cause temporary service disruption if critical services are stopped during the process. Mitigate by scheduling updates during maintenance windows.
- Roll back: 1) Revert the yum transaction using
sudo yum history undo. 2) Restore from the pre-update snapshot if necessary.
8. References and Resources
- Vendor advisory or bulletin: https://alas.aws.amazon.com/ALAS-2020-1455.html
- NVD or CVE entry: https://access.redhat.com/security/cve/CVE-2020-15257
- Product or platform documentation relevant to the fix: https://docs.aws.amazon.com/AmazonLinux/latest/ReleaseNotes/ALAS-2020-1455.html