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Medium, CVSS 5.0

Envoy's TLS certificate matcher for match_typed_subject_alt_names may incorrectly treat certificates containing an embedded null byte

CVE-2025-66220GHSA-rwjg-c3h2-f57p

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (github.com/envoyproxy/envoy 1.36.3, 1.35.7, 1.34.11, 1.33.13), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • Go github.com/envoyproxy/envoy

    Affected
    >= 1.36.0, <= 1.36.2>= 1.35.0, <= 1.35.6>= 1.34.0, <= 1.34.10<= 1.33.12
    Fixed in
    1.33.13, 1.36.3, 1.35.7, 1.34.11

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
5.0 · CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:L/A:N
EPSS
  • CVE-2025-66220: 0.18% estimated exploitation activity in the next 30 days; percentile 7.59 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary Envoy’s mTLS certificate matcher for matchtypedsubjectaltnames may incorrectly treat certificates containing an embedded null byte (\0) inside an OTHERNAME SAN value as valid matches. Details This occurs when the SAN is encoded as a BMPSTRING or UNIVERSALSTRING, and its UTF-8 conversion result is truncated at the first null byte during string assignment. As a result, "victim\0evil" may match an exact: "victim" rule and be accepted by Envoy. PoC Create a CA and a server certificate signed by that CA. Create two client certificates signed by the same CA: clientevil with OTHERNAME BMPSTRING = "evil" clientnull with OTHERNAME BMPSTRING = "victim\0evil" Configure Envoy with requireclientcertificate: true and a matchtypedsubjectaltnames entry for the OTHERNAME OID with matcher.exact: "victim". Connect without a client cert → connection rejected. Connect with clientevil → connection rejected. Connect with clientnull → connection accepted (but shouldn't!). Impact An attacker who can…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-rwjg-c3h2-f57p

Agent brief

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# Patch Next advisory brief: CVE-2025-66220

Advisory: Envoy's TLS certificate matcher for `match_typed_subject_alt_names` may incorrectly treat certificates containing an embedded null byte
IDs: CVE-2025-66220, GHSA-rwjg-c3h2-f57p
Record: https://patchnext.com/advisories/cve-2025-66220 (revision 1, source checked 26 Oct 2026, 15:13 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.0)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/envoyproxy/envoy 1.36.3, 1.35.7, 1.34.11, 1.33.13. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/envoyproxy/envoy: affected >= 1.36.0, <= 1.36.2; >= 1.35.0, <= 1.35.6; >= 1.34.0, <= 1.34.10; <= 1.33.12; fixed in 1.33.13, 1.36.3, 1.35.7, 1.34.11

## Suggested inspection (read-only)
- Go github.com/envoyproxy/envoy: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/envoyproxy/envoy.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-rwjg-c3h2-f57p (GitHub-reviewed advisory GHSA-rwjg-c3h2-f57p lists affected ranges: Go github.com/envoyproxy/envoy >=1.36.0 =1.35.0 =1.34.0 =0 <=1.33.12)

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