CVE-2025-64763 LOW

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

Vendor Envoyproxy
Product envoy
Weakness CWE-693
Published December 3, 2025
Last update December 3, 2025
View on NVD All CVEs

CVSS base score

3.7/10
Attack vector Network
Attack complexity High
Privileges required None
User interaction None
Confidentiality Low
Integrity None

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

December 3, 2025 CVE published
December 3, 2025 Record updated