1. Introduction
The Xerver Double Slash Authentication Bypass vulnerability allows unauthenticated access to protected web directories on affected servers. This occurs because of a flaw in how Xerver handles directory requests, potentially exposing sensitive data and functionality. Systems running vulnerable versions of Xerver are at risk. A successful exploit could compromise confidentiality, integrity, and availability of web-hosted content.
2. Technical Explanation
The vulnerability stems from insufficient path sanitisation within the Xerver web server software. By prepending an extra forward slash to a directory path in a URL request, an attacker can bypass authentication checks if the target directory is not recursively protected. This allows access to files and resources that should require login credentials.
- Root cause: Missing input validation on web directory paths allowing duplicate slashes.
- Scope: Xerver versions are affected; specific versions were not identified in the provided information but multiple other vulnerabilities may also be present.
3. Detection and Assessment
Confirming vulnerability requires checking the installed Xerver version and testing directory access with a modified URL.
- Quick checks: There is no command listed in the provided context to check the Xerver version directly. Check server configuration files for version information.
- Scanning: Nessus signature ID may identify this vulnerability, but other scanners should be checked.
- Logs and evidence: Examine web server access logs for requests containing duplicate slashes preceding directory paths. Look for successful access to protected directories without authentication.
4. Solution / Remediation Steps
Currently, there is no known solution available for this vulnerability. Mitigation focuses on limiting access and monitoring for exploitation attempts.
4.1 Preparation
- Dependencies: No specific dependencies are listed in the context.
- Roll back plan: Restore from the pre-change backup if issues arise.
4.2 Implementation
- Step 1: Implement strict access controls on protected directories, limiting access to only authorized users.
- Step 2: Monitor web server logs for suspicious activity and unauthorized access attempts.
4.3 Config or Code Example
Before
After
4.4 Security Practices Relevant to This Vulnerability
Practices that address this vulnerability include least privilege and input validation.
- Practice 1: Least privilege restricts access, limiting the impact of a successful exploit.
- Practice 2: Input validation can block requests with malformed directory paths, preventing bypass attempts.
4.5 Automation (Optional)
No automation script is provided in the context.
5. Verification / Validation
Verify that access controls are working as expected and monitor logs for exploitation attempts.
- Post-fix check: Attempt to access protected directories with a modified URL (e.g., ‘//example/protected’). Access should be denied.
- Re-test: Review web server logs for failed access attempts using the duplicate slash method.
- Smoke test: Verify that authorized users can still access protected directories normally.
- Monitoring: Monitor web server access logs for requests containing duplicate slashes preceding directory paths, and alert on any successful accesses.
6. Preventive Measures and Monitoring
Update security baselines to include input validation rules and a regular patch review cycle.
- Baselines: Update your web server security baseline to enforce strict access controls and input validation.
- Pipelines: Implement SAST or DAST tools in CI/CD pipelines to identify similar vulnerabilities during development.
- Asset and patch process: Review Xerver updates regularly for security patches.
7. Risks, Side Effects, and Roll Back
Implementing strict access controls may disrupt legitimate users if not configured carefully.
- Roll back: Restore the server from the pre-change backup to revert any configuration changes.
8. References and Resources
Links to official advisories and documentation are provided below.
- Vendor advisory or bulletin: http://www.nessus.org/u?bfed227d
- NVD or CVE entry: Not provided in the context.
- Product or platform documentation relevant to the fix: Not provided in the context.