CVE-2025-64763Network attack vector

Information disclosure via premature CONNECT data forwarding

Published Dec 3, 2025 · Updated Dec 3, 2025

Protection mechanism failure in Envoy affected versions allows remote attackers to disclose data through early CONNECT requests. In TCP proxy mode, Envoy forwards client bytes to the upstream TCP connection before an upstream proxy accepts the tunnel with a 2xx response. Exploitation requires early data and an upstream intermediary that rejects CONNECT; the resulting tunnel desynchronization has limited confidentiality impact, with no integrity or availability impact reported.

CVSS severity3.7
Low
EPSS probability0.30%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Protection mechanism failure in Envoy affected versions allows remote attackers to disclose data through early CONNECT requests. In TCP proxy mode, Envoy forwards client bytes to the upstream TCP connection before an upstream proxy accepts the tunnel with a 2xx response. Exploitation requires early data and an upstream intermediary that rejects CONNECT; the resulting tunnel desynchronization has limited confidentiality impact, with no integrity or availability impact reported.

The record

CVE
CVE-2025-64763
Published
Dec 3, 2025
Updated
Dec 3, 2025
Vendor
Envoy Proxy
Product
Envoy
Classifications
CWE-693, CWE-444
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 3, 2025CVE publishedPublication date reported by the CVE source.
  2. Dec 3, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=<= 1.33.12
  2. Affected versionversion=>= 1.34.0, <= 1.34.10
  3. Affected versionversion=>= 1.35.0, <= 1.35.6
  4. Affected versionversion=>= 1.36.0, <= 1.36.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Envoy Proxy · Envoyversion=<= 1.33.12; version=>= 1.34.0, <= 1.34.10; version=>= 1.35.0, <= 1.35.6; version=>= 1.36.0, <= 1.36.2

Published CVSS scores

5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
3.7GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-693Protection Mechanism Failure
CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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