Bug 2418664 (CVE-2025-64763) - CVE-2025-64763 Envoy: Envoy: De-synchronized CONNECT tunnel state due to early data handling in TCP proxy mode
Summary: CVE-2025-64763 Envoy: Envoy: De-synchronized CONNECT tunnel state due to earl...
Keywords:
Status: NEW
Alias: CVE-2025-64763
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Product Security DevOps Team
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Blocks:
TreeView+ depends on / blocked
 
Reported: 2025-12-03 19:02 UTC by OSIDB Bzimport
Modified: 2026-01-05 10:03 UTC (History)
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Description OSIDB Bzimport 2025-12-03 19:02:09 UTC 
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.
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