1. Introduction
Missing Function Level Access Control means the web application doesn’t properly restrict who can use certain features. This allows users with limited permissions to access functions they shouldn’t, potentially compromising data and system integrity. Web applications are commonly affected. A successful exploit could lead to unauthorised data access, modification or deletion.
2. Technical Explanation
- Root cause: Lack of authorisation checks on sensitive functions within the web application code.
- Exploit mechanism: An attacker crafts a malicious HTTP request to access a restricted function, bypassing normal user interface controls. For example, directly accessing an admin panel URL without authentication or with forged credentials.
- Scope: All web applications are potentially affected, particularly those using custom authorisation logic.
3. Detection and Assessment
Confirming vulnerability requires checking access to privileged functions. Start with a quick check of user permissions, then perform thorough testing.
- Quick checks: Log in as a standard user and attempt to access administrative URLs or features directly via the browser address bar.
- Scanning: Burp Suite or OWASP ZAP can be used to identify potentially accessible functions through crawling and active scanning (examples only).
- Logs and evidence: Examine web application logs for unauthorised access attempts to sensitive endpoints, looking for error messages related to permissions or authorisation failures.
curl -v 'https://example.com/admin/delete_user' # Check if a standard user can reach the admin panel URL. Look for 403 Forbidden responses as expected.4. Solution / Remediation Steps
Fixing this issue requires implementing proper authorisation checks on all privileged functions. Follow these steps carefully to ensure security and stability.
4.1 Preparation
- No services need to be stopped, but testing should occur in a non-production environment first. Roll back involves restoring the previous backup or snapshot.
- Changes require approval from the security team and a planned change window.
4.2 Implementation
- Step 1: Review all code that handles user requests, identifying functions with administrative or privileged capabilities.
- Step 2: Implement authorisation checks at the beginning of each privileged function to verify the current user has the necessary permissions.
- Step 3: Ensure authorisation logic is robust and cannot be bypassed through URL manipulation or other techniques.
- Step 4: Thoroughly test all privileged functions with different user roles to confirm access control is working as expected.
4.3 Config or Code Example
Before
def delete_user(username):
# Delete user without any permission check
...After
def delete_user(username):
if not current_user.is_admin():
return "Permission denied"
# Delete user only if the user is an admin
...4.4 Security Practices Relevant to This Vulnerability
Several security practices can help prevent this issue. Implementing least privilege reduces the impact of a successful exploit, while input validation prevents attackers from manipulating requests.
- Practice 1: Least privilege – grant users only the minimum permissions required for their tasks.
- Practice 2: Input validation – ensure all user inputs are properly sanitised and validated to prevent malicious data from reaching the application logic.
4.5 Automation (Optional)
If using a CI/CD pipeline, static code analysis tools can help identify missing authorisation checks during development.
# Example SonarQube rule:
# Rule ID: SXXXX - Detects functions without access control checks.
# Configure the tool to flag these instances as security vulnerabilities.5. Verification / Validation
Confirming the fix requires re-testing access to privileged functions with a standard user account. Ensure that unauthorised access is now blocked.
- Post-fix check: Log in as a standard user and attempt to access administrative URLs or features directly via the browser address bar. Expect 403 Forbidden responses.
- Re-test: Repeat the initial detection steps (Section 3) to confirm that unauthorised access is no longer possible.
- Smoke test: Verify core application functionality still works for standard users, such as logging in, viewing data, and submitting forms.
- Monitoring: Monitor web application logs for any attempts to access restricted endpoints, flagging unusual activity or error messages related to authorisation failures (example only).
curl -v 'https://example.com/admin/delete_user' # Should return 403 Forbidden after the fix.6. Preventive Measures and Monitoring
Updating security baselines and incorporating checks into CI pipelines can prevent similar issues in the future. Regular patch reviews are also important.
- Baselines: Update your web application security baseline to include requirements for function level access control (for example, CIS Benchmarks).
- Pipelines: Add static code analysis tools to your CI pipeline to identify missing authorisation checks during development.
- Asset and patch process: Implement a regular review cycle for all web application code and configurations to ensure security best practices are followed.
7. Risks, Side Effects, and Roll Back
- Risk or side effect 1: Overly restrictive access control rules may prevent valid users from performing their tasks. Mitigation: Carefully review and test all changes with representative user accounts.
- Risk or side effect 2: Performance impact due to increased authorisation checks. Mitigation: Optimise the authorisation logic for efficiency.
- Roll back: Restore the previous backup of the web application code and database. If a snapshot was taken, revert to that state.
8. References and Resources
- Vendor advisory or bulletin: Check your web application vendor’s security advisories for specific guidance on access control issues.
- NVD or CVE entry: Search the National Vulnerability Database (NVD) for related vulnerabilities, although a general entry may not exist for this broad issue.
- Product or platform documentation relevant to the fix: Refer to your web application framework’s documentation for guidance on implementing authorisation controls.