How severe is GHSA-rj35-4m94-77jh?

GHSA-rj35-4m94-77jh has a CVSS score of 3.7/10, rated LOW. Review your exposure and patch according to your risk tolerance.

Which packages are affected by GHSA-rj35-4m94-77jh?

GHSA-rj35-4m94-77jh affects the following packages: github.com/envoyproxy/envoy (Go), github.com/envoyproxy/envoy (Go), github.com/envoyproxy/envoy (Go), github.com/envoyproxy/envoy (Go). Ecosystems affected: Go.

How do I fix GHSA-rj35-4m94-77jh?

Update github.com/envoyproxy/envoy to 1.36.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-rj35-4m94-77jh is resolved across your whole dependency graph.

How do I detect GHSA-rj35-4m94-77jh in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/envoyproxy/envoy, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate GHSA-rj35-4m94-77jh if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is GHSA-rj35-4m94-77jh actively exploited in the wild?

No public exploit code has been indexed for GHSA-rj35-4m94-77jh yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for GHSA-rj35-4m94-77jh?

GHSA-rj35-4m94-77jh has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 23th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is GHSA-rj35-4m94-77jh?

GHSA-rj35-4m94-77jh is classified as CWE-693 (CWE-693). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was GHSA-rj35-4m94-77jh published, and has it been updated?

GHSA-rj35-4m94-77jh was published on December 5, 2025 and was last updated on December 10, 2025. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

LOW severity

Envoy forwards early CONNECT data in TCP proxy modeGHSA-rj35-4m94-77jh

LOW

GHSA-rj35-4m94-77jh is a low-severity (CVSS 3.7) CWE-693 vulnerability in github.com/envoyproxy/envoy. A fix is available for github.com/envoyproxy/envoy — see the affected versions and patch details below.

Also known asBIT-envoy-2025-64763CVE-2025-64763

Published

Dec 5, 2025

Updated

Dec 10, 2025

Affected

4 pkgs

Patched

4 / 4

Exploits

None indexed

Exploitation data as of Nov 2, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-rj35-4m94-77jh.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs23th percentile — riskier than 23% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

4 pkgs affected

🐹github.com/envoyproxy/envoy🐹github.com/envoyproxy/envoy🐹github.com/envoyproxy/envoy🐹github.com/envoyproxy/envoy

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Summary

Forwarding of early CONNECT data in TCP proxy mode.

Details

Per RFC 7231-4.3.6 the sender of CONNECT (and all inbound proxies) switch to tunnel mode only after receiving 2xx response. However in TCP proxy mode, Envoy accepts client data before it has issued a 2xx response and eagerly proxies it to an established TCP connection. This creates possibility of a de-synchronized tunnel state if a proxy upstream from Envoy responds with a status other an 2xx.

The RFC does not specify the behavior in case an early CONNECT data is received and early CONNECT data is common as a latency reduction mechanism. To prevent disruption to existing deployments Envoy will by default allow early CONNECT data. Setting the envoy.reloadable_features.reject_early_connect_data runtime flag to true will cause CONNECT requests that send data before 2xx response to be rejected. This options should be enabled if there are intermediaries upstream from Envoy that may reject establishment of a CONNECT tunnel.

Impact

De-synchronization of CONNECT tunnel state if a forwarding proxy upstream from Envoy responds with a non 2xx status.

Attack vector(s)

Sending data for a CONNECT request before receiving 2xx response.

Patches

Users should upgrade to v1.36.3, v1.35.7, v1.34.11 or v1.33.13

Credits

chasingimpact (Patrick)

Affected Packages

4 total 4 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/envoyproxy/envoy`	≥ 1.36.0&&< 1.36.3	1.36.3`go get github.com/envoyproxy/envoy@v1.36.3`
🐹Go	`github.com/envoyproxy/envoy`	≥ 1.35.0&&< 1.35.7	1.35.7`go get github.com/envoyproxy/envoy@v1.35.7`
🐹Go	`github.com/envoyproxy/envoy`	≥ 1.34.0&&< 1.34.11	1.34.11`go get github.com/envoyproxy/envoy@v1.34.11`
🐹Go	`github.com/envoyproxy/envoy`	all versions	1.33.13`go get github.com/envoyproxy/envoy@v1.33.13`

Affected Products

1 product · 4 configurations

Application

envoyenvoyproxy

≥ 1.36.0 && < 1.36.3

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/envoyproxy/envoy, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/envoyproxy/envoy to 1.36.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-rj35-4m94-77jh is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

This vulnerability is rated Moderate for Red Hat. Envoy, when operating in TCP proxy mode for CONNECT requests, forwards client data before a 2xx response. This can lead to a de-synchronized CONNECT tunnel state if an upstream proxy rejects the tunnel establishment. This behavior is enabled by default in affected…

Workaround published by Red Hat

To mitigate this issue, set the `envoy.reloadable_features.reject_early_connect_data` runtime flag to reject CONNECT requests that send data before a 2xx response. This configuration change may require a service reload or restart to take effect.

Source: Red Hat security advisory for GHSA-rj35-4m94-77jh (CC BY 4.0)

Frequently Asked Questions

## Summary Forwarding of early CONNECT data in TCP proxy mode. ## Details Per [RFC 7231-4.3.6](https://www.rfc-editor.org/rfc/rfc7231#section-4.3.6) the sender of CONNECT (and all inbound proxies) switch to tunnel mode only after receiving 2xx response. However in TCP proxy mode, Envoy accepts client data before it has issued a 2xx response and eagerly proxies it to an established TCP connection. This creates possibility of a de-synchronized tunnel state if a proxy upstream from Envoy responds with a status other an 2xx. The RFC does not specify the behavior in case an early CONNECT data

O3 Security · Impact-Aware SCA

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CVSS Score

3.7/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

None

Availability

None

Raw vector

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

CWE Classification

CWE-693CWE-693

Weaponization

No Nuclei template, Metasploit module or public proof-of-concept found.

OpenSSF Scorecard

Package health score

envoy

8.4/10

Maintained10/10

Code-Review9/10

Dependency-Update-Tool10/10

Vulnerabilities0/10

Branch-Protection4/10

Assessed Nov 2, 2026

Timeline

Disclosed

Dec 5, 2025

Last updated

Dec 10, 2025

Identifiers

GHSA-rj35-4m94-77jh

BIT-envoy-2025-64763

References

Advisorynvd.nist.gov · CVE 2025 64763 Webgithub.com · GHSA rj35 4m94 77jh Packagegithub.com · envoy

Related vulnerabilities

This CVE is low severity; 8 of 8 other CVEs affecting envoy are rated as high or higher (top: high).

CVE-2026-26310CVE-2026-26309CVE-2026-26311CVE-2026-26330CVE-2026-26308CVE-2025-64527CVE-2025-64763CVE-2025-66220

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedDec 10, 2025

Envoy forwards early CONNECT data in TCP proxy modeGHSA-rj35-4m94-77jh

Exploitation Status

No confirmed exploitation observed yet

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Summary

Details

Impact

Attack vector(s)

Patches

Credits

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Fixing This On Your OS

Frequently Asked Questions

Is GHSA-rj35-4m94-77jh in your dependencies?