1. Introduction
The vulnerability “DOM Elements Excluded” refers to situations where certain DOM elements are intentionally excluded from security interactions due to entries in a DOM Exclusion list. This can occur during web application scanning, potentially leading to incomplete assessments and missed vulnerabilities. It primarily affects web applications using automated scanning tools and could result in a false sense of security if critical elements are overlooked. The likely impact is low on confidentiality, integrity, and availability as it relates to assessment accuracy rather than direct exploitation.
2. Technical Explanation
The root cause is the configuration of DOM Exclusion lists within web application scanning tools. These lists define specific DOM elements that should be ignored during analysis, often for performance or compatibility reasons. An attacker could exploit this by crafting malicious content within excluded elements, which may not be detected by the scanner. The precondition is a configured DOM Exclusion list and an automated scan process.
- Root cause: Configuration of DOM Exclusion lists in web application scanners.
- Exploit mechanism: An attacker injects malicious code into DOM elements excluded from scanning, bypassing security checks. For example, injecting JavaScript within an element defined in the exclusion list.
- Scope: Web applications using automated scanning tools with configured DOM Exclusion lists.
3. Detection and Assessment
Confirming whether a system is vulnerable involves reviewing scanner configurations and scan results. A quick check is to examine the scanner’s configuration for any defined exclusion lists. A thorough method is to manually inspect the application source code and rendered DOM for elements that are excluded from scanning but contain sensitive data or functionality.
- Quick checks: Review the web application scanner’s configuration files for DOM Exclusion list settings.
- Scanning: Not applicable – this issue relates to scan configuration, not a directly scannable vulnerability.
- Logs and evidence: Examine scanner logs for messages related to excluded elements during scans.
4. Solution / Remediation Steps
The solution involves carefully reviewing and minimizing the use of DOM Exclusion lists in web application scanners. Only exclude elements when absolutely necessary, and ensure that any excluded elements do not contain sensitive data or critical functionality.
4.1 Preparation
- Dependencies: Ensure you have access to modify the web application scanner’s configuration. A roll back plan is to restore the original scanner configuration file if issues arise.
- Change window: Coordinate with security and development teams for any potential impact on scan results.
4.2 Implementation
- Step 1: Review the current DOM Exclusion list in your web application scanner’s configuration.
- Step 2: Remove any unnecessary exclusions from the list.
- Step 3: If exclusions are required, document the reason for each exclusion and assess the associated risk.
- Step 4: Save the updated scanner configuration.
4.3 Config or Code Example
Before
# Example exclusion list (insecure)
exclude_elements = ["#excluded-element1", ".excluded-class"]After
# Example exclusion list (more secure)
exclude_elements = [] # Remove unnecessary exclusions. Document any remaining ones.4.4 Security Practices Relevant to This Vulnerability
Several security practices are relevant to this vulnerability type. Least privilege helps reduce the impact if an excluded element is exploited. Input validation can prevent malicious code from being injected into DOM elements. Safe defaults ensure that scanners are configured with a secure baseline configuration.
- Practice 1: Least privilege – limit the scope of exclusions to only what’s necessary.
- Practice 2: Input validation – validate all user inputs to prevent malicious code injection.
4.5 Automation (Optional)
Not applicable – this issue is best addressed through manual configuration review and risk assessment.
5. Verification / Validation
Confirm the fix by re-running a web application scan with the updated configuration. Verify that previously excluded elements are now being scanned and assessed for vulnerabilities. Perform a simple service smoke test to ensure that core application functionality remains unaffected.
- Re-test: Re-run the web application scan and verify that all expected elements are being scanned.
- Monitoring: Monitor scanner logs for any unexpected errors or changes in scan results.
6. Preventive Measures and Monitoring
Update security baselines to reflect best practices for web application scanner configuration, including minimizing the use of DOM Exclusion lists. Incorporate checks in CI/CD pipelines to validate scanner configurations against these baselines. Establish a regular patch or config review cycle to ensure that scanners are up-to-date and securely configured.
- Baselines: Update security baselines with guidance on minimizing DOM exclusion lists.
- Pipelines: Add checks in CI/CD pipelines to validate scanner configurations against the baseline.
- Asset and patch process: Implement a regular review cycle for scanner configurations (e.g., quarterly).
7. Risks, Side Effects, and Roll Back
Removing exclusions may increase scan time or identify new vulnerabilities that were previously hidden. If issues arise, restore the original scanner configuration file to revert the changes.
- Risk or side effect 1: Increased scan time due to more elements being scanned. Mitigation: Optimize scan settings and hardware resources.
- Risk or side effect 2: Identification of new vulnerabilities in previously excluded elements. Mitigation: Prioritize remediation based on risk assessment.
- Roll back: Restore the original scanner configuration file from backup.
8. References and Resources
No specific references are available for this particular issue, as it relates to scanner configuration rather than a direct vulnerability. Consult your web application scanner’s documentation for guidance on configuring exclusion lists.
- Vendor advisory or bulletin: Refer to the documentation of your specific web application scanner vendor.
- NVD or CVE entry: Not applicable – this is not a directly exploitable vulnerability.
- Product or platform documentation relevant to the fix: Consult your web application scanner’s configuration guide.