1. Introduction
The Zimbra Collaboration Server aspell.php dictionary Parameter XSS vulnerability is a cross-site scripting flaw in the spell check service. Attackers can inject malicious code into a user’s browser, potentially stealing cookies or performing actions on their behalf. This affects systems running vulnerable versions of Zimbra Collaboration Server and could impact confidentiality, integrity, and availability depending on the injected script.
2. Technical Explanation
The vulnerability occurs because the ‘aspell.php’ script does not properly sanitise user input provided to the ‘dictionary’ parameter. This allows an attacker to inject arbitrary HTML and JavaScript code. An attacker could craft a malicious URL that, when visited by a user, executes their injected script within the user’s browser session. The vulnerability is tracked as CVE-2013-1938.
- Root cause: Insufficient input validation on the ‘dictionary’ parameter of the aspell.php script.
- Exploit mechanism: An attacker crafts a URL containing malicious JavaScript within the ‘dictionary’ parameter, which is then executed in the victim’s browser when they access the link. For example:
http://example.com/aspell.php?dictionary= - Scope: Zimbra Collaboration Server spell check service. Affected versions are not explicitly detailed in available documentation, but reports suggest older versions are vulnerable.
3. Detection and Assessment
Confirming vulnerability requires checking the installed Zimbra version and testing input sanitisation. A quick check is to determine the server version. More thorough assessment involves attempting to inject a simple XSS payload.
- Quick checks: Use the Zimbra Admin Console or command-line tools to display the Zimbra Collaboration Server version.
- Scanning: Nessus plugin ID 68913 may detect this vulnerability, but results should be verified manually.
- Logs and evidence: Examine web server logs for requests containing suspicious characters in the ‘dictionary’ parameter of aspell.php. Look for script tags or other HTML elements.
# Example command placeholder:
# Zimbra version check (command varies depending on installation type)
zimbra -v
4. Solution / Remediation Steps
A solution is currently unknown at this time. The following steps outline a process for monitoring and potential mitigation, pending an official patch from Zimbra.
4.1 Preparation
- No services need to be stopped at this stage.
4.2 Implementation
- Step 1: Monitor the OSS Security mailing list and the Zimbra Bugzilla for official updates or patches.
- Step 2: If a patch becomes available, download and install it according to Zimbra’s documentation.
4.3 Config or Code Example
Before
# No specific config example available as this is a code-level vulnerability.
# The issue lies in the aspell.php script's handling of user input.
After
# After applying an official patch, verify that the aspell.php script properly sanitises input to the 'dictionary' parameter. This requires code review or testing after patching.
4.4 Security Practices Relevant to This Vulnerability
Several security practices can help prevent this type of issue. Input validation is key, as is least privilege.
- Practice 1: Implement strict input validation on all user-supplied data to block potentially malicious characters and code.
- Practice 2: Apply the principle of least privilege to limit the impact if an attacker successfully exploits a vulnerability.
4.5 Automation (Optional)
No automation is available at this time due to lack of a known fix. Scripting could be used to monitor for new Zimbra releases, but requires custom development.
# Example script placeholder:
# This is an example only and needs significant customization.
# It would involve checking the Zimbra website or RSS feed for updates.
5. Verification / Validation
- Post-fix check: Verify the Zimbra version has been updated to the patched release.
- Re-test: Attempt to inject the same XSS payload as before (
http://example.com/aspell.php?dictionary=). The script should not execute. - Monitoring: Monitor web server logs for any attempts to inject malicious code into the ‘dictionary’ parameter of aspell.php.
# Post-fix command and expected output:
# zimbra -v
# Expected Output: Zimbra Collaboration Server 8.x.x (patched version)
6. Preventive Measures and Monitoring
Regular security baselines and patch management are important for preventing this issue. Consider adding input validation checks to your CI/CD pipeline.
- Baselines: Update your security baseline to include the latest Zimbra Collaboration Server version with all available patches.
- Pipelines: Implement Static Application Security Testing (SAST) tools in your CI/CD pipeline to identify potential vulnerabilities in custom code or configurations.
- Asset and patch process: Establish a regular patch review cycle for Zimbra Collaboration Server, ideally within 30 days of release.
7. Risks, Side Effects, and Roll Back
Patching may introduce compatibility issues with existing integrations. Always test in a non-production environment first.
- Risk or side effect 1: Patching could cause temporary service disruption.
- Risk or side effect 2: Compatibility issues with third-party plugins or integrations.
8. References and Resources
- Vendor advisory or bulletin: https://seclists.org/oss-sec/2013/q2/28
- NVD or CVE entry: CVE-2013-1938
- Product or platform documentation relevant to the fix: https://bugzilla.zimbra.com/show_bug.cgi?id=81588