Content-Encoding WAF Evasion

FortiWeb WAF policies can be bypassed by unauthenticated attackers using crafted Content-Encoding requests (CVSS 4.8).

Fortinet disclosed an incomplete list of disallowed inputs (CWE-184) in FortiWeb's WAF, tracked as FG-IR-26-157. An unauthenticated attacker can bypass WAF policies using specifically crafted requests with crafted Content-Encoding values. The issue carries a CVSSv3 score of 4.8 and was revised on 2026-08-12. The advisory does not report active exploitation.

• Incomplete input filtering (CWE-184) allows unauthenticated WAF policy bypass
• Crafted Content-Encoding requests evade the FortiWeb disallowed-input list
• CVSSv3 4.8; no exploitation reported in the advisory