VulnerabilityPublished 3 Dec 2025

CVE-2025-64763: envoyproxy envoy · Protection Mechanism Failure

Affects envoyproxy envoySource CVE Database V5

Not known to be exploited · CVSS 3.7 Low.

Data as of 26 Oct 2026, 12:55 UTC

CVSS 3.1 base score

3.7Low

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 22% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: None
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 3 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
GitHubenvoyproxy/envoy`pkg:github/envoyproxy/envoy`Other threats	Affected <=1.33.12	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

To mitigate CVE-2025-64763, European organizations should: 1) Identify all Envoy proxy instances running affected versions (<=1.36.2) configured in TCP proxy mode handling CONNECT requests. 2) Enable the runtime flag envoy.reloadable_features.reject_early_connect_data to reject early client data before a 2xx response, preventing tunnel state desynchronization. This flag can be set dynamically without restarting Envoy, allowing gradual rollout. 3) Where possible, upgrade Envoy to a version beyond 1.36.2 where this behavior is corrected or better controlled. 4) Review upstream proxy configurations to ensure they do not reject CONNECT requests unexpectedly, reducing the chance of state desynchronization. 5) Implement monitoring and alerting on proxy connection errors and tunnel failures to detect potential issues early. 6) Test proxy chains in staging environments to validate CONNECT request handling and early data acceptance behavior. 7) Document and train network and security teams on this vulnerability to ensure rapid response if issues arise. These steps go beyond generic patching advice by focusing on configuration flags, upstream proxy coordination, and operational monitoring specific to this vulnerability.

Description

CVE-2025-64763 is a low-severity vulnerability in Envoy proxy versions up to 1.36.2 that affects TCP proxy mode handling of CONNECT requests. Envoy accepts client data before sending a 2xx response and forwards it upstream, which can cause a de-synchronized CONNECT tunnel state if an upstream proxy rejects the connection with a non-2xx status. This behavior can lead to protocol state inconsistencies but does not directly impact confidentiality, integrity, or availability. The vulnerability arises from a protection mechanism failure (CWE-693) and can be mitigated by enabling the runtime flag envoy.reloadable_features.reject_early_connect_data to reject early data. No known exploits are reported in the wild, and the CVSS score is 3.7 (low).

Impact

For European organizations, the impact of CVE-2025-64763 is generally low but context-dependent. Organizations using Envoy as a TCP proxy in service meshes, cloud-native applications, or edge proxy deployments may experience connection disruptions or degraded service reliability if upstream proxies reject CONNECT requests and early client data is forwarded. This could lead to intermittent failures in establishing TCP tunnels, affecting applications relying on CONNECT-based proxying such as HTTPS proxying or tunneling protocols. While the vulnerability does not directly compromise data confidentiality or integrity, the desynchronized tunnel state could cause operational issues, increased troubleshooting complexity, and potential denial of service in proxy chains. Organizations with strict compliance or high availability requirements should consider this risk more seriously. The lack of known exploits reduces immediate threat, but the vulnerability could be leveraged in targeted attacks to disrupt proxy services. European cloud service providers, telecom operators, and enterprises with complex proxy infrastructures are most at risk. The impact on availability and operational continuity is the primary concern rather than data breach or privilege escalation.

CWE-693Protection Mechanism Failure (opens in a new tab)
Pillar weaknessOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product.
MITRE discourages mapping vulnerabilities to this broad entry; the root cause is usually a more specific weakness.
OWASP Cheat Sheets
Secure Design Principles (opens in a new tab)
Attack patterns
Accessing Functionality Not Properly Constrained by ACLs (opens in a new tab)
Cross Site Tracing (opens in a new tab)
Directory Indexing (opens in a new tab)
Using Malicious Files (opens in a new tab)
Encryption Brute Forcing (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

github.com/envoyproxy/envoy/security/advisories/GHSA-rj35-4m94-77jh (opens in a new tab)

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 10 Dec 2025, 20:02 UTC

WeaknessesCWE-693

Technical details

References

Community reviews

Related threats