CVE-2025-64763
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-12-03

Last updated on: 2025-12-05

Assigner: GitHub, Inc.

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.
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Meta Information
Published
2025-12-03
Last Modified
2025-12-05
Generated
2026-06-16
AI Q&A
2025-12-03
EPSS Evaluated
2026-06-15
NVD
CVE-2025-64763
Affected Vendors & Products
Showing 4 associated CPEs
Vendor Product Version / Range
envoyproxy envoy to 1.33.13 (exc)
envoyproxy envoy From 1.34.0 (inc) to 1.34.11 (exc)
envoyproxy envoy From 1.35.0 (inc) to 1.35.7 (exc)
envoyproxy envoy From 1.36.0 (inc) to 1.36.3 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-693 The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product.
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Executive Summary

This vulnerability occurs in Envoy when it is configured in TCP proxy mode to handle CONNECT requests. Envoy accepts client data before sending a 2xx success response and forwards that data upstream. If an upstream proxy then responds with a non-2xx status, it can cause a de-synchronized CONNECT tunnel state. This happens because Envoy forwards early data before the connection is fully established, potentially leading to communication issues.

Impact Analysis

The vulnerability can cause a de-synchronized CONNECT tunnel state, which may disrupt communication between clients and upstream servers. This could lead to unexpected behavior or failures in establishing TCP tunnels through Envoy, potentially impacting the reliability of network connections that depend on CONNECT tunnels.

Mitigation Strategies

To mitigate this vulnerability, set the runtime flag envoy.reloadable_features.reject_early_connect_data to reject CONNECT requests that send data before a 2xx response. This prevents Envoy from accepting early client data that could cause a de-synchronized CONNECT tunnel state when upstream proxies reject the connection.

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