Envoy Proxy Incorrect Authorization Vulnerability - CVE-2026-26308

Envoy is a high-performance edge/middle/service proxy. Prior to 1.37.1 1.36.5 1.35.8 and 1.34.13 the Envoy RBAC (Role-Based Access Control) filter contains a logic vulnerability in how it validates HTTP headers when multiple values are present for the same header name. Instead of validating each header value individually Envoy concatenates all values into a single comma-separated string. This behavior allows attackers to bypass RBAC policiesspecifically quotDenyquot rulesby sending duplicate headers effectively obscuring the malicious value from exact-match mechanisms. This vulnerability is fixed in 1.37.1 1.36.5 1.35.8 and 1.34.13.