Atomicorp WAF Rule 340035

Rule Summary

• Rule ID: 340035
• Status: Active
• Alert message: Atomicorp.com WAF Rules: Bogus file extensions
• Observed CWEs: CWE-434 (1)
• Revision: 5
• Rule severity: Critical (2)
• Phase: 2 (request body)
• Request surfaces: Request URI
• Rule action: deny
• HTTP status: 403
• Logging: log, auditlog

Description

This rule detects “bogus” file extensions, that is file extensions that should not be valid. For example, a file named “shell.php.wmv”. This method is used by attackers to try to bypass upload managers that try to enforce valid files by looking at file extensions, and deny certain types of files.

False Positives

A false positive can occur when a file or application is legitimately named in this non-standard fashion. We recommend that you follow a standard naming convention, as most upload managers will also follow these conventions and allowing non-standard files may allow an attacker to bypass the file type checks in some web applications.

The rules also contain a large library of known web applications and safe methods that use non standard naming conventions, and can detect known safe methods and ignore them. However it is possible for a new or custom application to do this in an unknown manner and incorrectly trigger this rule.

It is not recommended that you disable this rule if you have a false positive. If you believe this is a false positive, please report this to our security team to determine if this is a legitimate case, or if its clever attack on your system. Instructions to report false positives are detailed on the Reporting False Positives wiki page. If it is a false positive, we will fix the issue in the rules and get a release out to you promptly.

Tuning Guidance

If you know that this behavior is acceptable for your application, you can tune by following the guidance on the Tuning the Atomicorp WAF Rules page.

Selected Related CVEs

This is a selected list of documented research observations, not an exhaustive coverage matrix. Absence of a CVE does not imply absence of protection.

Observed CWEs

These CWEs are recorded on published CVEs in the selected observations associated with this rule. They are observational relationships, not a claim that the rule universally blocks every vulnerability assigned to a CWE.

Documentation Source

• Original wiki page: WAF 340035
• Source revision: 1717
• Source revision date: 2011-07-20