CVE-2026-26308

Envoy has an RBAC Header Validation Bypass via Multi-Value Header Concatenation

State: Published
Severity: 7.5 High
Published: Mar 10, 2026
Updated: Mar 10, 2026
Reserved: Feb 13, 2026

Description

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.

Scores

CVSS	Score	Vector	Source
3.1	7.5 High	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N	GitHub_M

Weaknesses

CWE-863 Incorrect Authorization

Affected Products

Product	Versions
envoyenvoyproxy	>= 1.37.0, < 1.37.1Affected >= 1.36.0, < 1.36.5Affected >= 1.35.0, < 1.35.9Affected < 1.34.13Affected

References

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