Envoy up to 1.33.12/1.34.10/1.35.6/1.36.2 TCP Connection protection mechanism

CVSS Meta Temp Score CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.	Current Exploit Price (≈) Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.	CTI Interest Score Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
4.2	$0-$5k	0.00

Summaryinfo

A vulnerability identified as problematic has been detected in Envoy up to 1.33.12/1.34.10/1.35.6/1.36.2. This issue affects some unknown processing of the component TCP Connection Handler. The manipulation leads to protection mechanism. This vulnerability is uniquely identified as CVE-2025-64763. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in Envoy up to 1.33.12/1.34.10/1.35.6/1.36.2. This issue affects some unknown functionality of the component TCP Connection Handler. The manipulation with an unknown input leads to a protection mechanism vulnerability. Using CWE to declare the problem leads to CWE-693. The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product. Impacted is confidentiality. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2025-64763 since 11/10/2025. The exploitation is known to be difficult. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 01/06/2026).

The vulnerability scanner Nessus provides a plugin with the ID 281808 (Amazon Linux 2 : ecs-service-connect-agent, --advisory ALAS2ECS-2025-093 (ALASECS-2025-093)), which helps to determine the existence of the flaw in a target environment.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the databases at Tenable (281808) and EUVD (EUVD-2025-201099). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Name

• Envoy

Version

• 1.33.0
• 1.33.1
• 1.33.2
• 1.33.3
• 1.33.4
• 1.33.5
• 1.33.6
• 1.33.7
• 1.33.8
• 1.33.9
• 1.33.10
• 1.33.11
• 1.33.12
• 1.34.0
• 1.34.1
• 1.34.2
• 1.34.3
• 1.34.4
• 1.34.5
• 1.34.6
• 1.34.7
• 1.34.8
• 1.34.9
• 1.34.10
• 1.35.0
• 1.35.1
• 1.35.2
• 1.35.3
• 1.35.4
• 1.35.5
• 1.35.6
• 1.36.0
• 1.36.1
• 1.36.2

License

• free

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 4.2
VulDB Meta Temp Score: 4.2

VulDB Base Score: 3.7
VulDB Temp Score: 3.7
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 5.3
NVD Vector: 🔒

CNA Base Score: 3.7
CNA Vector (GitHub_M): 🔒

CVSSv2info

AV	AC	Au	C	I	A
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳

Vector	Complexity	Authentication	Confidentiality	Integrity	Availability
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock

VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Protection mechanism
CWE: CWE-693
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

0-Day	Unlock	Unlock	Unlock	Unlock
Today	Unlock	Unlock	Unlock	Unlock

Nessus ID: 281808
Nessus Name: Amazon Linux 2 : ecs-service-connect-agent, --advisory ALAS2ECS-2025-093 (ALASECS-2025-093)

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: no mitigation known
Status: 🔍

0-Day Time: 🔒

Timelineinfo

11/10/2025 CVE reserved
12/03/2025 +23 days Advisory disclosed
12/03/2025 +0 days VulDB entry created
01/06/2026 +34 days VulDB entry last update

Sourcesinfo

Advisory: GHSA-rj35-4m94-77jh
Status: Confirmed

CVE: CVE-2025-64763 (🔒)
GCVE (CVE): GCVE-0-2025-64763
GCVE (VulDB): GCVE-100-334217
EUVD: 🔒

Entryinfo

Created: 12/03/2025 23:43
Updated: 01/06/2026 13:16
Changes: 12/03/2025 23:43 (61), 12/05/2025 20:45 (1), 12/06/2025 00:05 (11), 01/06/2026 13:16 (2)
Complete: 🔍
Cache ID: 216::103

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Discussion

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