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EnvoyApplication · Envoyproxy

CVE-2026-26308

HIGH · 8.2 CVSS v3.1 Published 2026-03-10
Fix available
A fix is available. Upgrade to 1.34.13 / 1.35.8 or later.
See remediation →
91/100
Remediation priority · Urgent
Public exploit Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-863

An authorization check exists but is flawed, so it passes when it should fail. Attackers probe roles and object references to find the gap. Remediation means centralising and correctly implementing the access-control logic, then testing it against every role.

General guidance for the incorrect authorization class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
EnvoyApplication
Affected:< 1.34.13>= 1.35.0, < 1.35.8>= 1.36.0, < 1.36.5= 1.37.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 1.34.13 / 1.35.8 / 1.36.5 or later
Fixed in 1.34.131.35.81.36.5
Vendor patch github.com →
Recommended fix High confidence

Upgrade to Envoy 1.37.1 (or the appropriate patched version for your branch: 1.36.5, 1.35.8, or 1.34.13)

  1. Identify the currently running Envoy version using 'envoy --version' or checking the deployment manifests
  2. Plan the upgrade to a fixed version based on your current major.minor branch (e.g., if on 1.37.x upgrade to 1.37.1, if on 1.36.x upgrade to 1.36.5, etc.)
  3. Download the fixed Envoy release from the official releases (https://github.com/envoyproxy/envoy/releases) for your target version
  4. Replace the Envoy binary in your deployment pipeline (CI/CD), container registry, or infrastructure
  5. Review existing RBAC policies to understand which headers are being checked for authorization decisions
  6. Deploy the upgraded Envoy to a staging or testing environment
  7. Validate that RBAC Deny rules correctly block requests with duplicate headers (e.g., multiple 'Authorization' headers with a benign value followed by a malicious value)
  8. Deploy to production after successful validation
Caveat Review Envoy release notes for any breaking changes between your current version and the target fixed version; major version upgrades may have configuration or API changes

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,950. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-26308 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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