CVE-2025-64763

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.

CVSS v3.1 Score

3.7

LOW

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

Weakness Type (CWE)

CWE-693 CWE-693

Affected Products

Vendor	Product	Versions
envoyproxy	envoy	< 1.33.13
envoyproxy	envoy	1.34.0 — 1.34.11
envoyproxy	envoy	1.35.0 — 1.35.7
envoyproxy	envoy	1.36.0 — 1.36.3

References

Advisories & Patches

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

Frequently Asked Questions

What is 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. It has a CVSS v3.1 base score of 3.7 (LOW).

How severe is CVE-2025-64763? +

CVE-2025-64763 has a CVSS v3.1 score of 3.7 out of 10, rated LOW. This is a low-severity vulnerability with limited impact.

What products are affected by CVE-2025-64763? +

CVE-2025-64763 affects products from envoyproxy, specifically: envoy. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-64763? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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