# CVE-2026-47778: Envoy: Embedded NUL in TLS DNS SAN Truncation in the Default TLS Certificate Validator. (Auth Bypass)

> Attackers can bypass TLS certificate validation by using embedded NUL bytes in DNS SANs, allowing unauthorized upstream routing.

- **Severity:** Medium 4.4 (`CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:N/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:** 26 Jun 2026
- **Updated:** 27 Jun 2026
- **Also known as:** BIT-envoy-2026-47778, GHSA-f8x4-rw5x-f3r7

## What is CVE-2026-47778?

CVE-2026-47778 is a medium-severity authentication bypass vulnerability in Envoyproxy Envoy, published on 26 Jun 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.35.11, 1.36.7, 1.37.3, and 1.38.1, a structural flaw was identified in DefaultCertValidator::verifySubjectAltName where the extracted DNS SAN string is cast to a C-style string using .c_str() before being passed to the Utility::dnsNameMatch() algorithm. If the attacker serves a certificate with a dNSName SAN containing an embedded NUL byte, the helper Utility::generalNameAsString captures the complete string including the NUL. However, when .c_str() evaluates it, implicit conversion to absl::string_view inside dnsNameMatch relies on strlen(), prematurely truncating the evaluation context. Envoy evaluates trucated string against the exact required config_san match and returns true, thereby successfully validating the string with the Nul byte for an upstream routing. This vulnerability is fixed in 1.35.11, 1.36.7, 1.37.3, and 1.38.1.

Weakness: CWE-158 (Improper Neutralization of Null Byte or NUL Character)

## Which versions are affected by CVE-2026-47778?

1 open source package ship an affected version, including envoy. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `envoy` | Bitnami | All versions | 1.35.11, 1.36.7, 1.37.3, 1.38.1 |

Products: Envoyproxy Envoy.

## How do I fix CVE-2026-47778?

Upgrade envoy to a fixed version for your release line: 1.35.11, 1.36.7, 1.37.3 or 1.38.1.

## Is CVE-2026-47778 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-47778 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-2026-47778 and fix it if it is affected.

What it is: CVE-2026-47778 is a medium-severity authentication bypass vulnerability in Envoyproxy Envoy, published on 26 Jun 2026. 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-2026-47778 exists.

Affected packages and fixed versions:
- envoy (Bitnami): affected all versions; fixed in 1.35.11, 1.36.7, 1.37.3, 1.38.1

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-2026-47778/ (Markdown: https://insights.sbomify.com/CVE-2026-47778/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-47778
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-47778
- OSV: https://osv.dev/vulnerability/CVE-2026-47778

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-47778/
Summaries are generated and may contain mistakes; the official description above is the record.