CVE-2026-26308: Envoyproxy Envoy

High severity, CVSS 8.2. EPSS: 0.4% chance of exploitation in the next 30 days.

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 policies—specifically "Deny" rules—by 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.

Affected products

• Envoyproxy Envoy: before 1.34.13 (fixed in 1.34.13); from 1.35.0, before 1.35.8 (fixed in 1.35.8); from 1.36.0, before 1.36.5 (fixed in 1.36.5); version 1.37.0 only

Published 2026-03-10. Last modified 2026-06-17.