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TI-2026-21264 Aliases CVE-2026-26308GHSA-ghc4-35x6-crw5

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

Priority LOW 36CWE-863Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Security bypass
Confidentiality · integrity · availability
High · Low · None
Fix status
Fixed

Attack profile from CVSS 3.1 · NVD. Fix status from CNA and GitHub. Impact type from CWE-863.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00323 25th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Fixed envoy (envoyproxy): 1.37.1, 1.36.5, 1.35.9 +1github.com/envoyproxy/envoy (Go): 1.37.1, 1.36.5, 1.35.9 +1

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
envoyproxyenvoy1.37.0 to before 1.37.1; 1.36.0 to before 1.36.5; 1.35.0 to before 1.35.9; before 1.34.131.37.1, 1.36.5, 1.35.9, 1.34.13Patch availableCNA
—github.com/envoyproxy/envoy (Go)1.37.0 to before 1.37.11.37.1Patch availableGHSA-ghc4-35x6-crw5
—github.com/envoyproxy/envoy (Go)1.36.0 to before 1.36.51.36.5Patch availableGHSA-ghc4-35x6-crw5
—github.com/envoyproxy/envoy (Go)1.35.0 to before 1.35.91.35.9Patch availableGHSA-ghc4-35x6-crw5
—github.com/envoyproxy/envoy (Go)before 1.34.131.34.13Patch availableGHSA-ghc4-35x6-crw5
  • envoy Vendorenvoyproxy Affected 1.37.0 to before 1.37.1; 1.36.0 to before 1.36.5; 1.35.0 to before 1.35.9; before 1.34.13 Fixed in 1.37.1, 1.36.5, 1.35.9, 1.34.13 Patch available CNA
  • github.com/envoyproxy/envoy (Go) Vendor— Affected 1.37.0 to before 1.37.1 Fixed in 1.37.1 Patch available GHSA-ghc4-35x6-crw5
  • github.com/envoyproxy/envoy (Go) Vendor— Affected 1.36.0 to before 1.36.5 Fixed in 1.36.5 Patch available GHSA-ghc4-35x6-crw5
  • github.com/envoyproxy/envoy (Go) Vendor— Affected 1.35.0 to before 1.35.9 Fixed in 1.35.9 Patch available GHSA-ghc4-35x6-crw5
  • github.com/envoyproxy/envoy (Go) Vendor— Affected before 1.34.13 Fixed in 1.34.13 Patch available GHSA-ghc4-35x6-crw5

CPE configurations NVD · 2

CPEVersionsRoleVendor
cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*before 1.34.13; 1.35.0 to before 1.35.8; 1.36.0 to before 1.36.5Vulnerableenvoyproxy
cpe:2.3:a:envoyproxy:envoy:1.37.0:*:*:*:*:*:*:*1.37.0Vulnerableenvoyproxy
  • cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:* Versions before 1.34.13; 1.35.0 to before 1.35.8; 1.36.0 to before 1.36.5 Vulnerable ·envoyproxy
  • cpe:2.3:a:envoyproxy:envoy:1.37.0:*:*:*:*:*:*:* Versions 1.37.0 Vulnerable ·envoyproxy

Remediation

  • Fix · CNA envoy (envoyproxy) Fixed in 1.37.1, 1.36.5, 1.35.9, 1.34.13
  • Fix · GHSA-ghc4-35x6-crw5 github.com/envoyproxy/envoy (Go) Fixed in 1.37.1 Advisory →
  • Fix · GHSA-ghc4-35x6-crw5 github.com/envoyproxy/envoy (Go) Fixed in 1.36.5 Advisory →
  • Fix · GHSA-ghc4-35x6-crw5 github.com/envoyproxy/envoy (Go) Fixed in 1.35.9 Advisory →
  • Fix · GHSA-ghc4-35x6-crw5 github.com/envoyproxy/envoy (Go) Fixed in 1.34.13 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-26308
  2. 2026-10-03 Alias added: GHSA-ghc4-35x6-crw5

References

Exploit 1

Patch 1

Advisory 1

Other 1

  • TI-2026-79288 Out-of-bounds write in Google Brotli decoder KEVCVSS 4.0CRITICAL 9.2
  • TI-2023-23979 The HTTP/2 protocol allows a denial of service (server resource consumption) because… KEVCVSS 3.1HIGH 7.5
  • TI-2024-20001 HTTP/2: CPU exhaustion due to CONTINUATION frame flood CVSS 3.1HIGH 7.5
  • TI-2024-18524 HTTP/2: memory exhaustion due to CONTINUATION frame flood CVSS 3.1HIGH 7.5
  • TI-2023-12215 Envoy client may fake the header `x-envoy-original-path` CVSS 3.1CRITICAL 9.1
  • TI-2023-18002 Envoy vulnerable to OAuth2 credentials exploit with permanent validity CVSS 3.1CRITICAL 9.8
See all 126 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences