How to remediate – IBM Lotus Notes/Domino Square Brackets Encoding Failure XSS

1. Introduction

IBM Lotus Notes/Domino is prone to a cross-site scripting (XSS) vulnerability when handling requests for .nsf files with html arguments. This allows an attacker to inject malicious scripts into web pages viewed by other users, potentially stealing cookies or performing actions on their behalf. Systems running vulnerable versions of IBM Lotus Notes/Domino are affected. A successful exploit could lead to a loss of confidentiality, integrity and availability depending on the injected script.

2. Technical Explanation

The vulnerability occurs because the server does not properly encode user-supplied input when reflecting it back in web responses. Specifically, when requesting a .nsf file with html arguments (e.g., /FormReflectingURLValue?OpenForm&Field=[XSS]), the input is included directly into the HTML output without sanitization. This allows an attacker to inject arbitrary JavaScript code that will be executed in the victim’s browser. The vulnerability is tracked as CVE-2004-1621.

• Root cause: Insufficient input validation and encoding of user-supplied data within URL parameters when generating HTML responses.
• Exploit mechanism: An attacker crafts a malicious URL containing JavaScript code in the Field parameter, then tricks a victim into visiting that URL. The injected script executes in the victim’s browser context. For example: http://example.com/FormReflectingURLValue?OpenForm&Field=
• Scope: IBM Lotus Notes and Domino versions prior to those with fixes for CVE-2004-1621 are affected.

3. Detection and Assessment

You can confirm if a system is vulnerable by checking the version of IBM Lotus Notes/Domino and testing its response to malicious URLs.

• Quick checks: Use the ‘notes -c "show server"‘ command in the Domino console to display the server version.
• Scanning: Nessus plugin ID 10862 may detect this vulnerability, but results should be verified manually.
• Logs and evidence: Examine web server logs for requests containing suspicious URL parameters like ‘OpenForm&Field=‘. Look for encoded script tags in the responses.

notes -c "show server"
# Example output (vulnerable version):
Server name: example.com
Version: 6.5.2FP1
...

4. Solution / Remediation Steps

Currently, there is no official solution available for this vulnerability. Mitigation focuses on limiting exposure and monitoring for exploitation attempts.

4.1 Preparation

• No services need to be stopped for testing but consider a change window if implementing workarounds. A roll back plan involves restoring from backup.

4.2 Implementation

1. Step 1: Implement web application firewall (WAF) rules to block requests containing suspicious URL parameters like ‘OpenForm&Field=‘.
2. Step 2: Monitor web server logs for exploitation attempts and investigate any detected malicious activity.

4.3 Config or Code Example

Before

After

# Example WAF rule (syntax varies by vendor)
# Block requests containing "OpenForm&Field=" in the URL.
# This is a mitigation only and does not fix the root cause.
block url contains "OpenForm&Field="

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help mitigate this vulnerability type.

• Practice 2: Output encoding prevents injected scripts from being executed in the browser.

4.5 Automation (Optional)

5. Verification / Validation

Confirm that the fix works by testing whether malicious URLs are blocked and that injected scripts do not execute.

• Post-fix check: Attempt to access a vulnerable URL (e.g., http://example.com/FormReflectingURLValue?OpenForm&Field=). The WAF should block the request and prevent the script from executing.
• Smoke test: Ensure legitimate users can still access and use core Lotus Notes/Domino functionality, such as mail and calendar features.
• Monitoring: Monitor web server logs for any attempts to exploit this vulnerability or similar XSS attacks.

# Example WAF log entry (syntax varies by vendor)
# Blocked request due to "OpenForm&Field=" in URL.
timestamp: 2024-10-27 10:00:00
status: blocked
url: http://example.com/FormReflectingURLValue?OpenForm&Field=

6. Preventive Measures and Monitoring

Update security baselines and implement checks in CI pipelines to prevent similar vulnerabilities.

• Baselines: Update a web server security baseline or policy to require input validation and output encoding for all user-supplied data.
• Asset and patch process: Maintain a regular patch review cycle, prioritizing critical security updates.

7. Risks, Side Effects, and Roll Back

Implementing WAF rules may cause false positives, blocking legitimate traffic.

• Risk or side effect 1: False positives from WAF rules can disrupt service availability. Monitor logs carefully and adjust rules as needed.
• Roll back: Remove the WAF rule to restore normal functionality. Restore from backup if necessary.

8. References and Resources

• Vendor advisory or bulletin: http://www.securityfocus.com/bid/11458
• NVD or CVE entry: CVE-2004-1621
• Product or platform documentation relevant to the fix: No specific documentation available, as there is no patch.