# CVE-2025-66220: Envoy's TLS certificate matcher for `match_typed_subject_alt_names` may incorrectly treat certificates containing an embedded null byte

> Attackers can bypass mTLS authentication by using certificates with embedded null bytes in SAN values, allowing unauthorized access to protected services.

- **Severity:** Medium 5.0 (`CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 3 Dec 2025
- **Updated:** 3 Dec 2025
- **Also known as:** BIT-envoy-2025-66220, GHSA-rwjg-c3h2-f57p

## What is CVE-2025-66220?

CVE-2025-66220 is a medium-severity vulnerability in Envoyproxy Envoy, published on 3 Dec 2025. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

Envoy is a high-performance edge/middle/service proxy. In 1.33.12, 1.34.10, 1.35.6, 1.36.2, and earlier, Envoy’s mTLS certificate matcher for match_typed_subject_alt_names may incorrectly treat certificates containing an embedded null byte (\0) inside an OTHERNAME SAN value as valid matches.

Weakness: CWE-170 (Improper Null Termination)

## Which versions are affected by CVE-2025-66220?

9 open source packages ship an affected version, including github.com/envoyproxy/envoy and envoy. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/envoyproxy/envoy` | Go | All versions | 1.33.13 |
| `github.com/envoyproxy/envoy` | Go | All versions | 1.33.13 |
| `github.com/envoyproxy/envoy` | Go | From 1.34.0 | 1.34.11 |
| `github.com/envoyproxy/envoy` | Go | From 1.34.0 | 1.34.11 |
| `github.com/envoyproxy/envoy` | Go | From 1.35.0 | 1.35.7 |
| `github.com/envoyproxy/envoy` | Go | From 1.35.0 | 1.35.7 |
| `github.com/envoyproxy/envoy` | Go | From 1.36.0 | 1.36.3 |
| `github.com/envoyproxy/envoy` | Go | From 1.36.0 | 1.36.3 |
| `envoy` | Bitnami | All versions | 1.33.13, 1.34.11, 1.35.7, 1.36.3 |

Products: Envoyproxy Envoy.

## How do I fix CVE-2025-66220?

Upgrade github.com/envoyproxy/envoy to a fixed version for your release line: 1.33.13, 1.34.11, 1.35.7 or 1.36.3.

## Is CVE-2025-66220 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-66220 exists.

## Other vulnerabilities in Envoyproxy Envoy

- [CVE-2022-29226](https://insights.sbomify.com/CVE-2022-29226/): Trivial authentication bypass in Envoy (critical 10.0)
- [CVE-2019-18801](https://insights.sbomify.com/CVE-2019-18801/): Memory corruption in n/a (critical 9.8)
- [CVE-2019-18802](https://insights.sbomify.com/CVE-2019-18802/): Security feature bypass in n/a (critical 9.8)
- [CVE-2020-35470](https://insights.sbomify.com/CVE-2020-35470/): Information disclosure in n/a (high 8.8)
- [CVE-2024-23324](https://insights.sbomify.com/CVE-2024-23324/): Envoy ext auth can be bypassed when Proxy protocol filter sets invalid UTF-8 metadata (high 8.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-66220 and fix it if it is affected.

What it is: CVE-2025-66220 is a medium-severity vulnerability in Envoyproxy Envoy, published on 3 Dec 2025. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-66220 exists.

Affected packages and fixed versions:
- github.com/envoyproxy/envoy (Go): affected all versions; fixed in 1.33.13
- github.com/envoyproxy/envoy (Go): affected all versions; fixed in 1.33.13
- github.com/envoyproxy/envoy (Go): affected from 1.34.0; fixed in 1.34.11
- github.com/envoyproxy/envoy (Go): affected from 1.34.0; fixed in 1.34.11
- github.com/envoyproxy/envoy (Go): affected from 1.35.0; fixed in 1.35.7
- github.com/envoyproxy/envoy (Go): affected from 1.35.0; fixed in 1.35.7
- github.com/envoyproxy/envoy (Go): affected from 1.36.0; fixed in 1.36.3
- github.com/envoyproxy/envoy (Go): affected from 1.36.0; fixed in 1.36.3
- envoy (Bitnami): affected all versions; fixed in 1.33.13, 1.34.11, 1.35.7, 1.36.3

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-66220/ (Markdown: https://insights.sbomify.com/CVE-2025-66220/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-66220
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-66220
- OSV: https://osv.dev/vulnerability/CVE-2025-66220

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-66220/
Summaries are generated and may contain mistakes; the official description above is the record.