Auth bypass in Envoyproxy Envoy
CVE-2026-26308
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.
Vulnerability class: Broken Access Control
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N.
EPSS exploit prediction
EPSS: 0.003 (25.5th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 26th percentile — 25.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: +0.001
Affected products
- Envoyproxy Envoy — versions >= 1.37.0, < 1.37.1, 1.37.0, < 1.34.13
Weakness classification (CWE)
References
- github.com/envoyproxy/envoy/security/advisories/GHSA-ghc4-35x6-crw5 (Exploit, Mitigation, Vendor Advisory)
- github.com/envoyproxy/envoy/commit/b6ba0b2294b98484fb0ed8556897d1073cc27867 (Patch)
Frequently asked questions
- What is CVE-2026-26308?
- CVE-2026-26308 is a high-severity vulnerability in Envoyproxy Envoy, classified under Incorrect Authorization. CVSS score: 7.5/10. Published 2026-03-10.
- How severe is CVE-2026-26308?
- High severity. CVSS v3 base score is 7.5 out of 10.