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

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

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.

Products include 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 Trivial authentication bypass in Envoy Critical 10.0
• CVE-2019-18801 Memory corruption in n/a Critical 9.8
• CVE-2019-18802 Security feature bypass in n/a Critical 9.8
• CVE-2020-35470 Information disclosure in n/a High 8.8
• CVE-2024-23324 Envoy ext auth can be bypassed when Proxy protocol filter sets invalid UTF-8 metadata High 8.6

All Envoyproxy Envoy vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BIT-envoy-2025-64763, GHSA-rj35-4m94-77jh.