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CVE-2025-64763

Envoy forwards early CONNECT data in TCP proxy mode

Published: Dec 3, 2025Updated: Dec 5, 2025 Sources: CVE List NVD GHSACWE-693
NVD MITRE
3.7CVSSLOW
EPSS Score
0.3%
Top 81.3%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

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 Vector Breakdown

AV:NAC:HPR:NUI:NS:UC:LI:NA:N
Exploitability
AV:NAttack Vector
Network
AC:HAttack Complexity
High
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:LConfidentiality
Low
I:NIntegrity
None
A:NAvailability
None
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Weaknesses

CWE-693

Affected Products

envoyenvoyproxy
On-prem
Cloud & SaaS / api-gateway
github.com/envoyproxy/envoyGoOSS Libraries
envoyproxyoss-projectUSCloud & SaaSaka envoy proxy, envoy
gopackage-ecosystemOSS Libraries

Exploitability

Official Patch Available

References

https://github.com/envoyproxy/envoy/security/advisories/GHSA-rj35-4m94-77jh
github.com
https://nvd.nist.gov/vuln/detail/CVE-2025-64763
nvd.nist.gov
https://github.com/envoyproxy/envoy
github.com

Timeline

Published
Dec 3, 2025
Last Updated
Dec 5, 2025

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