1. Introduction
2. Technical Explanation
The vulnerability lies within the ‘securecgi-bin/CSuserCGI.exe’ CGI script in ACS when handling arguments passed to the Help feature. Insufficient input validation allows an attacker to inject arbitrary JavaScript or HTML code via this argument. This injected code is then executed in the context of a user’s browser, enabling malicious actions. The vulnerability has been assigned CVE-2008-0533 and IAVB 2008-B-0025-S.
- Root cause: Missing input validation on arguments passed to the CSuserCGI.exe script’s Help argument.
- Exploit mechanism: An attacker crafts a malicious URL containing JavaScript code in the Help argument and sends it to a user or tricks them into visiting the crafted link. When the user accesses the URL, the injected script executes within their browser session. For example:
http://[target]/securecgi-bin/CSuserCGI.exe?Help= - Scope: Cisco Secure Access Control Server (ACS) for Windows and ACS Solution Engine versions prior to 4.2 are affected.
3. Detection and Assessment
To confirm vulnerability, check the installed version of ACS. A thorough assessment involves attempting to inject a simple XSS payload.
- Quick checks: Use the ACS web interface to determine the software version. Look for versions older than 4.2.
- Scanning: Nessus plugin ID 578e73a1 can detect this vulnerability. This is an example only, and other scanners may also provide detection capabilities.
- Logs and evidence: Monitor ACS web server logs for suspicious URL parameters containing script tags or encoded JavaScript code in the Help argument.
4. Solution / Remediation Steps
Apply the latest patch or upgrade ACS to a non-vulnerable version.
4.1 Preparation
- Stop the Cisco Secure Access Control Server service prior to patching. A roll back plan involves restoring from backup or reverting the system snapshot.
- A change window is recommended, and approval should be obtained from the security team.
4.2 Implementation
- Step 1: Download the latest ACS software version (4.2 or later) from Cisco’s website.
- Step 2: Stop the Cisco Secure Access Control Server service.
- Step 3: Install the new ACS software version, following the vendor’s installation instructions.
- Step 4: Restore the backed-up configuration to the upgraded ACS instance.
- Step 5: Start the Cisco Secure Access Control Server service.
4.3 Config or Code Example
Before
After
4.4 Security Practices Relevant to This Vulnerability
Input validation and secure coding practices are crucial for preventing XSS vulnerabilities.
- Practice 2: Safe defaults minimize attack surfaces. Ensure that ACS is configured with secure default settings and unnecessary features are disabled.
4.5 Automation (Optional)
No automation script provided as this requires software installation/upgrade.
5. Verification / Validation
Confirm the fix by verifying the ACS version and attempting to re-exploit the vulnerability.
- Post-fix check: Use the ACS web interface to confirm that the installed version is 4.2 or later.
- Re-test: Attempt to inject a simple XSS payload (e.g.,
http://[target]/securecgi-bin/CSuserCGI.exe?Help=). The script should not execute, and the browser should display the code as text. - Monitoring: Monitor web server logs for any attempts to exploit the Help argument.
6. Preventive Measures and Monitoring
Regular patching, security baselines, and secure coding practices are essential.
- Baselines: Update your security baseline to require ACS version 4.2 or later.
- Pipelines: Implement static application security testing (SAST) in your CI/CD pipeline to identify potential XSS vulnerabilities during development.
- Asset and patch process: Establish a regular patch review cycle for all critical systems, including ACS.
7. Risks, Side Effects, and Roll Back
Upgrading ACS may introduce compatibility issues with existing integrations or configurations.
- Risk or side effect 2: Service downtime during the upgrade process. Mitigation: Schedule the upgrade during a maintenance window.
- Roll back: Restore from the pre-upgrade ACS configuration backup. If a system snapshot was taken, revert to that state.
8. References and Resources
- Vendor advisory or bulletin: http://www.cisco.com/warp/public/707/cisco-sa-20080312-ucp.shtml
- NVD or CVE entry: CVE-2008-0533
- Product or platform documentation relevant to the fix: No specific documentation available beyond vendor advisory.