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Vulnerability · Published Dec 3, 2025 · Assigned by GitHub_M

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

Low 3.7

In plain English

A low-severity security flaw in envoy from envoyproxy. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 25% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)3.7Low
Exploit odds (30 days)0.3%top 74.5% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Gogithub.com/envoyproxy/envoy1.36.3GHSA-rj35-4m94-77jh
Gogithub.com/envoyproxy/envoy1.35.7GHSA-rj35-4m94-77jh
Gogithub.com/envoyproxy/envoy1.34.11GHSA-rj35-4m94-77jh
Gogithub.com/envoyproxy/envoy1.33.13GHSA-rj35-4m94-77jh

Affected products (as reported)

VendorProductVersions
envoyproxy envoy >= 1.36.0, <= 1.36.2>= 1.35.0, <= 1.35.6>= 1.34.0, <= 1.34.10<= 1.33.12

Weakness: CWE-693 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

References