Vulnerability in Envoyproxy Envoy

CVE-2025-64763

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.

Published · last modified .

CVSS v3 metric

CVSS v3 base score 3.7 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N.

EPSS exploit prediction

EPSS: 0.003 (20.6th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 21st percentile — 20.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2025-64763: held from 0.003 to 0.003.

EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: 0.000

Affected products

  • Envoyproxy Envoy — versions >= 1.36.0, <= 1.36.2, >= 1.35.0, <= 1.35.6, >= 1.34.0, <= 1.34.10

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2025-64763?
CVE-2025-64763 is a low-severity vulnerability in Envoyproxy Envoy, classified under Protection Mechanism Failure. CVSS score: 3.7/10. Published 2025-12-03.
How severe is CVE-2025-64763?
Low severity. CVSS v3 base score is 3.7 out of 10.