1. Introduction
The AIX bind Advisory : bind_advisory10.asc (IV80187) (IV80188) (I…) vulnerability affects versions of the BIND DNS server on AIX systems. This is a denial-of-service issue caused by improper parsing of malformed data, potentially leading to service crashes. Systems running vulnerable versions of bind are at risk of becoming unavailable. Impact: Confidentiality – None; Integrity – None; Availability – High.
2. Technical Explanation
The vulnerability in BIND (CVE-2015-8000) occurs due to a flaw in the db.c file when parsing class attributes within DNS records. A remote, unauthenticated attacker can send a crafted DNS request containing an incorrect class attribute that triggers a REQUIRE assertion failure, causing bind to crash and become unresponsive.
- Root cause: Improper parsing of malformed class attributes in the db.c file.
- Exploit mechanism: An attacker sends a malicious DNS query with a crafted class attribute designed to trigger an assertion failure within the bind process.
- Scope: AIX systems running vulnerable versions of BIND are affected.
3. Detection and Assessment
To confirm vulnerability, check the installed version of bind. A thorough assessment involves reviewing DNS logs for unexpected crashes or errors related to parsing failures.
- Quick checks: Use the following command to display the BIND version:
named -v - Scanning: Nessus plugin ID 79349 can detect this vulnerability as an example.
- Logs and evidence: Examine system logs (e.g., /var/log/messages) for crash reports or errors related to bind, specifically mentioning db.c or assertion failures.
named -v4. Solution / Remediation Steps
Apply the fix available from IBM AIX website. These steps ensure a safe and effective resolution of the vulnerability.
4.1 Preparation
- There are no specific dependencies, but ensure sufficient disk space for the update. Roll back plan: Restore from backup or revert to the previous system snapshot.
- A change window may be required depending on service criticality and availability requirements. Approval should be obtained from IT operations.
4.2 Implementation
- Step 1: Download the appropriate fix package for your AIX version from https://aix.software.ibm.com/aix/efixes/security/bind_advisory10.asc.
- Step 2: Install the fix package using the smit command:
smit apply. - Step 3: Reboot the AIX system to ensure the updated bind version is loaded and running.
4.3 Config or Code Example
Before
# No specific configuration changes are required before applying the patch. After
# After applying the patch, verify the updated bind version using named -v.4.4 Security Practices Relevant to This Vulnerability
Patch management is crucial for addressing vulnerabilities like this one. Regular security scans help identify vulnerable systems. Least privilege can limit the impact of a successful exploit.
- Practice 1: Implement a regular patch cadence to apply security updates promptly, reducing the window of opportunity for attackers.
4.5 Automation (Optional)
# Example Ansible playbook snippet (requires appropriate credentials and access):
# - name: Apply AIX patch for bind vulnerability
# ibm_aix_patch:
# bundle_id: bind_advisory10
# state: applied
# become: true
5. Verification / Validation
Confirm the fix by verifying the updated BIND version and re-testing for the vulnerability. A simple service smoke test should ensure DNS resolution continues to function normally.
- Post-fix check: Run
named -vand confirm the version is updated to a patched release. - Re-test: Re-run the initial detection method (e.g., Nessus scan) to verify the vulnerability is no longer detected.
- Smoke test: Verify DNS resolution by pinging a known hostname (e.g.,
ping google.com). - Monitoring: Monitor system logs for any errors related to bind, specifically looking for crashes or assertion failures.
named -v6. Preventive Measures and Monitoring
Update security baselines to include the patched BIND version. Implement automated vulnerability scanning in CI/CD pipelines. Establish a regular patch review cycle based on risk assessment.
- Baselines: Update your AIX security baseline or policy to require the latest patched version of bind.
- Asset and patch process: Implement a monthly patch review cycle for critical systems like DNS servers.
7. Risks, Side Effects, and Roll Back
- Risk or side effect 1: System reboot required, leading to brief DNS outage. Mitigate by scheduling during off-peak hours.
- Roll back: 1) Restore from backup if necessary. 2) Revert to the previous system snapshot if taken.
8. References and Resources
- Vendor advisory or bulletin: https://aix.software.ibm.com/aix/efixes/security/bind_advisory10.asc
- NVD or CVE entry: CVE-2015-8000
- Product or platform documentation relevant to the fix: IBM AIX Documentation for bind configuration and patching.