# CVE-2025-64763: Envoy forwards early CONNECT data in TCP proxy mode


- **Severity:** Low 3.7 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 3 Dec 2025
- **Updated:** 3 Dec 2025
- **Also known as:** BIT-envoy-2025-64763, GHSA-rj35-4m94-77jh

## What is CVE-2025-64763?

CVE-2025-64763 is a low-severity vulnerability in Envoyproxy Envoy, published on 3 Dec 2025. 

### 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, when Envoy is configured in TCP proxy mode to handle CONNECT requests, it accepts client data before issuing a 2xx response and forwards that data to the upstream TCP connection. If a forwarding proxy upstream from Envoy then responds with a non-2xx status, this can cause a de-synchronized CONNECT tunnel state. By default Envoy continues to allow early CONNECT data to avoid disrupting existing deployments. The envoy.reloadable_features.reject_early_connect_data runtime flag can be set to reject CONNECT requests that send data before a 2xx response when intermediaries upstream from Envoy may reject establishment of a CONNECT tunnel.

Weakness: CWE-693 (Protection Mechanism Failure)

## Which versions are affected by CVE-2025-64763?

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-2025-64763?

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-2025-64763 being exploited?

There is no known exploitation of CVE-2025-64763 in the wild and no public exploit code.

## 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-2025-64763 and fix it if it is affected.

What it is: CVE-2025-64763 is a low-severity vulnerability in Envoyproxy Envoy, published on 3 Dec 2025. 
Exploitation: There is no known exploitation of CVE-2025-64763 in the wild and no public exploit code.

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-2025-64763/ (Markdown: https://insights.sbomify.com/CVE-2025-64763/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-64763
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-64763
- OSV: https://osv.dev/vulnerability/CVE-2025-64763

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-64763/
Summaries are generated and may contain mistakes; the official description above is the record.