How to remediate – AIX OpenSSL Advisory : openssl_advisory5.asc

1. Introduction

The vulnerability “AIX OpenSSL Advisory : openssl_advisory5.asc” affects versions of OpenSSL running on AIX systems. It involves timing side-channel attacks and signature verification issues in OCSP responses, potentially allowing remote attackers to recover plaintext or cause a denial of service. This impacts the confidentiality, integrity, and availability of services relying on TLS/DTLS connections.

2. Technical Explanation

The vulnerability stems from flaws in how OpenSSL handles CBC padding during TLS/DTLS processing (Lucky Thirteen – CVE-2013-0169) and signature verification for OCSP responses (CVE-2013-0166). An attacker can exploit these weaknesses by sending crafted packets to the server, analyzing timing variations to recover plaintext data or trigger a crash. Exploitation requires network access to vulnerable systems.

• Root cause: The TLS protocol 1.1 and 1.2 do not properly consider timing side-channel attacks on MAC check requirements during processing of malformed CBC padding. OpenSSL does not properly perform signature verification for OCSP responses, leading to a NULL pointer dereference.
• Exploit mechanism: An attacker sends specially crafted TLS/DTLS packets and monitors the time it takes for the server to respond. Statistical analysis of these timings can reveal information about the plaintext data (Lucky Thirteen). For CVE-2013-0166, an invalid key in an OCSP response causes a crash.
• Scope: AIX systems running OpenSSL versions prior to 0.9.8y, 1.0.0k, and 1.0.1d are affected.

3. Detection and Assessment

Confirm vulnerability by checking the installed OpenSSL version. A thorough assessment involves reviewing system logs for potential exploitation attempts.

• Quick checks: Use the following command to check the OpenSSL version: openssl version
• Logs and evidence: Check system logs for crashes related to OpenSSL or TLS/DTLS connections. Look for error messages indicating signature verification failures.

openssl version

4. Solution / Remediation Steps

4.1 Preparation

• Create a mksysb backup of the system and verify it is bootable and readable. Stop any services that rely on OpenSSL if possible.
• The fix package can be downloaded from the AIX website. A roll back plan involves restoring the mksysb backup if issues occur.
• A change window may be required depending on your organization’s policies, with approval from system owners.

4.2 Implementation

1. Step 1: Extract the fix package using the following command: zcat openssl-0.9.8.2500.tar.Z | tar xvf - or zcat openssl-fips-12.9.8.2500.tar.Z | tar xvf -
2. Step 2: Preview the fix installation using the following command: installp -apYd . openssl
3. Step 3: Install the fix package using the following command: installp -aXYd . opensssl

4.3 Config or Code Example

No configuration changes are required; this is a patch installation.

Before

N/A - Vulnerable OpenSSL version installed.

After

N/A - Patched OpenSSL version installed.

4.4 Security Practices Relevant to This Vulnerability

Practices such as a robust patch management process and least privilege can help mitigate the impact of this vulnerability.

• Practice 1: Implement a regular patch cadence for all software, including OpenSSL, to address known vulnerabilities promptly.
• Practice 2: Apply the principle of least privilege by limiting access to sensitive services and data. This reduces the potential impact if an attacker exploits this vulnerability.

4.5 Automation (Optional)

Automation is not included as it depends on your specific environment and tools.

N/A

5. Verification / Validation

• Post-fix check: Run openssl version and verify that the output shows a patched version (0.9.8y or later, 1.0.0k or later, or 1.0.1d or later).
• Re-test: Re-run the command openssl version to confirm the updated version is installed.
• Monitoring: Monitor system logs for any new errors related to OpenSSL or TLS/DTLS connections, which could indicate a regression.

openssl version

6. Preventive Measures and Monitoring

Update security baselines to include the patched OpenSSL versions. Implement automated scanning in CI/CD pipelines to detect vulnerable configurations.

• Baselines: Update your security baseline or policy to require OpenSSL versions 0.9.8y or later, 1.0.0k or later, or 1.0.1d or later.
• Asset and patch process: Review and update your asset inventory and patch management process to ensure timely application of security updates.

7. Risks, Side Effects, and Roll Back

Applying the patch may cause temporary service disruptions. A roll back plan involves restoring the mksysb backup.

• Risk or side effect 1: Applying the patch could temporarily disrupt services that rely on OpenSSL. Mitigate by scheduling maintenance during off-peak hours and testing thoroughly in a non-production environment first.

8. References and Resources

Refer to IBM’s official advisory for detailed information about this vulnerability.

• Vendor advisory or bulletin: https://aix.software.ibm.com/aix/efixes/security/openssl_advisory5.asc
• NVD or CVE entry: CVE-2013-0166, CVE-2013-0169
• Product or platform documentation relevant to the fix: https://www14.software.ibm.com/webapp/iwm/web/preLogin.do?source=aixbp