CVE-2025-64763

Envoy forwards early CONNECT data in TCP proxy mode

State: Published
Severity: 3.7 Low
Published: Dec 3, 2025
Updated: Dec 3, 2025
Reserved: Nov 10, 2025

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.

Scores

CVSS	Score	Vector	Source
3.1	3.7 Low	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N	GitHub_M

Weaknesses

CWE-693 Protection Mechanism Failure

Affected Products

Product	Versions
envoyenvoyproxy	>= 1.36.0, <= 1.36.2Affected >= 1.35.0, <= 1.35.6Affected >= 1.34.0, <= 1.34.10Affected <= 1.33.12Affected

References

https://github.com/envoyproxy/envoy/security/advisories/GHSA-rj35-4m94-77jh

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