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5.3
MEDIUM CVSS 3.1
CVE-2025-64763
Envoy forwards early CONNECT data in TCP proxy mode
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.

INFO

Published Date :

Dec. 3, 2025, 6:15 p.m.

Last Modified :

Dec. 5, 2025, 4:52 p.m.

Remotely Exploit :

Yes !

Source :

[email protected]
Affected Products

The following products are affected by CVE-2025-64763 vulnerability. Even if cvefeed.io is aware of the exact versions of the products that are affected, the information is not represented in the table below.

ID Vendor Product Action
1 Envoyproxy envoy
: Total Affected Vendor : 1 | Products : 1
CVSS Scores
The Common Vulnerability Scoring System is a standardized framework for assessing the severity of vulnerabilities in software and systems. We collect and displays CVSS scores from various sources for each CVE.
Score Version Severity Vector Exploitability Score Impact Score Source
CVSS 3.1 LOW [email protected]
CVSS 3.1 MEDIUM [email protected]
Solution
Configure Envoy to reject early CONNECT data for improved security.
  • Enable envoy.reloadable_features.reject_early_connect_data.
  • Ensure upstream proxies respond correctly to CONNECT.
  • Update Envoy to a non-vulnerable version.
References to Advisories, Solutions, and Tools

Here, you will find a curated list of external links that provide in-depth information, practical solutions, and valuable tools related to CVE-2025-64763.

URL Resource
https://github.com/envoyproxy/envoy/security/advisories/GHSA-rj35-4m94-77jh Patch Vendor Advisory
CWE - Common Weakness Enumeration

While CVE identifies specific instances of vulnerabilities, CWE categorizes the common flaws or weaknesses that can lead to vulnerabilities. CVE-2025-64763 is associated with the following CWEs:

Common Attack Pattern Enumeration and Classification (CAPEC)

Common Attack Pattern Enumeration and Classification (CAPEC) stores attack patterns, which are descriptions of the common attributes and approaches employed by adversaries to exploit the CVE-2025-64763 weaknesses.

CAPEC-1: Accessing Functionality Not Properly Constrained by ACLs Accessing Functionality Not Properly Constrained by ACLs CAPEC-17: Using Malicious Files Using Malicious Files CAPEC-20: Encryption Brute Forcing Encryption Brute Forcing CAPEC-22: Exploiting Trust in Client Exploiting Trust in Client CAPEC-36: Using Unpublished Interfaces or Functionality Using Unpublished Interfaces or Functionality CAPEC-51: Poison Web Service Registry Poison Web Service Registry CAPEC-57: Utilizing REST's Trust in the System Resource to Obtain Sensitive Data Utilizing REST's Trust in the System Resource to Obtain Sensitive Data CAPEC-59: Session Credential Falsification through Prediction Session Credential Falsification through Prediction CAPEC-65: Sniff Application Code Sniff Application Code CAPEC-74: Manipulating State Manipulating State CAPEC-87: Forceful Browsing Forceful Browsing CAPEC-107: Cross Site Tracing Cross Site Tracing CAPEC-127: Directory Indexing Directory Indexing CAPEC-237: Escaping a Sandbox by Calling Code in Another Language Escaping a Sandbox by Calling Code in Another Language CAPEC-477: Signature Spoofing by Mixing Signed and Unsigned Content Signature Spoofing by Mixing Signed and Unsigned Content CAPEC-480: Escaping Virtualization Escaping Virtualization CAPEC-668: Key Negotiation of Bluetooth Attack (KNOB) Key Negotiation of Bluetooth Attack (KNOB)

We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).

Results are limited to the first 15 repositories due to potential performance issues.

The following list is the news that have been mention CVE-2025-64763 vulnerability anywhere in the article.

Results are limited to the first 20 news articles due to potential performance issues.

The following table lists the changes that have been made to the CVE-2025-64763 vulnerability over time.

Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.

  • Initial Analysis by [email protected]

    Dec. 05, 2025

    Action Type Old Value New Value
    Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
    Added CPE Configuration OR *cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:* versions from (including) 1.36.0 up to (excluding) 1.36.3 *cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:* versions up to (excluding) 1.33.13 *cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:* versions from (including) 1.34.0 up to (excluding) 1.34.11 *cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:* versions from (including) 1.35.0 up to (excluding) 1.35.7
    Added Reference Type GitHub, Inc.: https://github.com/envoyproxy/envoy/security/advisories/GHSA-rj35-4m94-77jh Types: Patch, Vendor Advisory
  • New CVE Received by [email protected]

    Dec. 03, 2025

    Action Type Old Value New Value
    Added 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.
    Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
    Added CWE CWE-693
    Added Reference https://github.com/envoyproxy/envoy/security/advisories/GHSA-rj35-4m94-77jh
EPSS is a daily estimate of the probability of exploitation activity being observed over the next 30 days. Following chart shows the EPSS score history of the vulnerability.
Vulnerability Scoring Details
Base CVSS Score: 5.3
Attack Vector
Attack Complexity
Privileges Required
User Interaction
Scope
Confidentiality Impact
Integrity Impact
Availability Impact