Skip to content
Fencer Vulns
high 7.5

CVE-2026-26308 json

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

published 2026-03-10 8 mo ago modified 2026-09-08 2 mo ago also BIT-envoy-2026-26308 , EUVD-2026-10798 , GHSA-ghc4-35x6-crw5

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 25%
public exploits
0
none known

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.

Patch / fix

  • go github.com/envoyproxy/envoy 1.34.13, 1.35.9, 1.36.5, 1.37.1
  • bitnami envoy 1.34.13, 1.35.9, 1.36.5, 1.37.1
  • envoyproxy envoy 1.34.13, 1.35.9, 1.36.5, 1.37.1

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
8 mo ago

Exploit prediction

0.32% chance of exploitation in the next 30 days, higher than 25% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/envoyproxy/envoy/security/advisories/GHSA-ghc4-35x6-crw5 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N
NVD 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
OSV 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

Affected packages

ecosystem package affected fixed in
go github.com/envoyproxy/envoy
>=1.37.0, <1.37.1
>=1.36.0, <1.36.5
>=1.35.0, <1.35.9
<1.34.13
1.37.1
1.36.5
1.35.9
1.34.13
bitnami envoy
<1.34.13
>=1.35.0, <1.35.9
>=1.36.0, <1.36.5
>=1.37.0, <1.37.1
1.34.13
1.35.9
1.36.5
1.37.1

Affected products

  • envoyproxy envoy

Classification

Weakness
  • CWE-863 Incorrect Authorization
  • CWE-20 Improper Input Validation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.