CVE-2025-64763
Envoy forwards early CONNECT data in TCP proxy mode
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.
How to fix CVE-2025-64763
To remediate CVE-2025-64763, upgrade the affected package to a fixed version below.
- —upgrade to 1.33.13 or later
- —upgrade to 1.36.3 or later
Is CVE-2025-64763 being exploited?
Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.
Affected packages (2)
- from 0, < 1.33.13, >= 1.34.0, < 1.34.11, >= 1.35.0, < 1.35.7, >= 1.36.0, < 1.36.3
- >= 1.36.0, < 1.36.3
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | LOW3.7 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N |