High 7.5Published Mar 10, 2026

CVE-2026-26308Envoy has an RBAC Header Validation Bypass via Multi-Value Header Concatenation

Updated under an hour ago (Oct 29, 2026, 9:50 PM ET)

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No exploitation reported and no EPSS estimate yet.

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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.

CVSS: 7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N
Weakness (CWE): CWE-863
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Analyzed
Record last updated: Mar 10, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

envoyproxy envoy envoyproxy:envoy (from the name)	from 1.37.0, < 1.37.1; from 1.36.0, < 1.36.5; from 1.35.0, < 1.35.9; before 1.34.13	CNA record
envoyproxy envoy envoyproxy:envoy	before 1.34.13; from 1.35.0 before 1.35.8; from 1.36.0 before 1.36.5; 1.37.0	NVD

References

References

https://github.com/envoyproxy/envoy/security/advisories/GHSA-ghc4-35x6-crw5	x-refsource-confirm, exploit, mitigation, vendor-advisory
https://github.com/envoyproxy/envoy/commit/b6ba0b2294b98484fb0ed8556897d1073cc27867	x-refsource-misc, patch

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.