What’s Vulnerable › Vulnerabilities
CVE-2025-64763: Envoy forwards early CONNECT data in TCP proxy mode
- Severity: medium (CVSS 5.3 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.3% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2025-12-03 · updated 2026-06-17
- Weakness: CWE-693
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.
Affected products
- envoyproxy envoy: before 1.33.13; from 1.34.0 before 1.34.11; from 1.35.0 before 1.35.7; from 1.36.0 before 1.36.3 — fixed in 1.33.13, 1.34.11, 1.35.7, 1.36.3
How to fix
Upgrade to a fixed version: envoyproxy envoy 1.33.13, 1.34.11, 1.35.7, 1.36.3. Check the vendor advisory for mitigations.
References
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