CVE-2025-64763 - CVE House
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Status published Low CVE-2025-64763

Envoy forwards early CONNECT data in TCP proxy mode

Vulnerability 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.

Impact Analysis

Refer to official advisory for detailed impact metrics.

Remediation

Ensure systems are updated to the latest vendor-supplied patch levels.

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Credits & Attribution

No credits recorded in the NVD database.

References

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Affected Vendor

Affected Software

envoy
Vulnerable Versions:
>= 1.36.0, <= 1.36.2, >= 1.35.0, <= 1.35.6, >= 1.34.0, <= 1.34.10, <= 1.33.12

Timeline

Official Publish: December 3rd, 2025
Last Modified: December 3rd, 2025
Added to House: July 22nd, 2026

CVSS Vectors

V3: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Weaknesses (CWE)

CWE-693

MITRE ATT&CK TTPs

T1562 Impair Defenses
Defense Evasion
T1190 Exploit Public-Facing Application
Initial Access
T1068 Exploitation for Privilege Escalation
Privilege Escalation
T1550 Use Alternate Authentication Material
Defense Evasion
T1485 Data Destruction
Impact