Atomicorp WAF Rule 390700

Rule Summary

• Rule ID: 390700
• Status: Active
• Alert message: Atomicorp.com WAF Rules: Evasion Attack: Invalid filename in FILES argument. Which may be a possible attempt at multipart/form-data bypass
• Observed CWEs: CWE-20 (3), CWE-22 (2), CWE-23 (1), CWE-73 (1), CWE-74 (1), CWE-77 (1), CWE-78 (7), CWE-79 (1), CWE-89 (5), CWE-91 (1), CWE-94 (1), CWE-264 (1), CWE-287 (5), CWE-288 (1), CWE-306 (7), CWE-434 (14), CWE-502 (1), CWE-668 (1), CWE-798 (1), CWE-862 (1), CWE-863 (1)
• Revision: 7
• Phase: 2 (request body)
• Request surfaces: Uploaded files
• Rule action: deny
• HTTP status: 403
• Logging: log, auditlog

Description

This rule can be triggered if an attacker attempts to bypass the WAF’s multipart assembler. There are several known attack methods that attempt to bypass WAFs by using this method.

Additionally, if any of the following characters are used in a filename this rule will be triggered:

“;=

These characters are not supported in the filename and are reserved characters.

False Positives

False Positives are rare with this rule. We do not recommend you disable this unless you want to ignore any evasion based on the multipart parser in the WAF. Currently there are no known vulnerabilities in the 2.5.12 version of the WAF (ASL versions 2.2.7 and up are not vulnerable). Therefore, if you know that your client sends an invalid multipart message when uploading a file, you are running the latest version of ASL and you do not care about detecting and blocking evasion based attacks disable this rule. We do not recommend you disable this rule, rather we recommend fixing the application to ensure that it does not accept broken multipart messages.

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.

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 390700
• Source revision: 4340
• Source revision date: 2013-12-19