Your RSA-2048 keys break in 2030. Find every one of them before attackers do.
📦
📦 npm
Not in CISA KEV
MEDIUM severity

Insecure Defaults Allow MITM Over TLS in engine.io-clientGHSA-4r4m-hjwj-43p8

MEDIUMFix: socketio/engine.io-client@2c55b27

GHSA-4r4m-hjwj-43p8 is a medium-severity (CVSS 5.9) CWE-300 vulnerability in engine.io-client. A fix is available for engine.io-client — see the affected versions and patch details below.

Also known asCVE-2016-10536
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.0%probability of exploitation in next 30 days
Lower Risk-0.02%
Lower risk than most CVEs62th percentile — riskier than 62% of all scored CVEsHighest risk
0.00%0.50%1.01%1.51%0.2%1.0%Apr 26Aug 26Oct 26

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

How urgent is this, really

GHSA-4r4m-hjwj-43p8 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 395,249 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

193other npm packages depend on this — each one inherits the vulnerability until it's patched upstream
engine.io-clientnpm
16.9Mdownloads / week

Description

engine.io-client is the client for engine.io, the implementation of a transport-based cross-browser/cross-device bi-directional communication layer for Socket.IO. The vulnerability is related to the way that node.js handles the rejectUnauthorized setting. If the value is something that evaluates to false, certificate verification will be disabled. This is problematic as engine.io-client 1.6.8 and earlier passes in an object for settings that includes the rejectUnauthorized property, whether it has been set or not. If the value has not been explicitly changed, it will be passed in as null, resulting in certificate verification being turned off.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
📦npmengine.io-clientall versions1.6.9npm install engine.io-client@1.6.9

Affected Products

1 product · 1 configurations
Application
engine.io-clientsocket
≤ 1.6.8
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

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

  2. Fix

    Update engine.io-client to 1.6.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-4r4m-hjwj-43p8 is resolved across your whole dependency graph.

  3. 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.

Frequently Asked Questions

Affected versions of `engine.io-client` do not verify certificates by default, and as such may be vulnerable to Man-in-the-Middle attacks. The vulnerability is related to the way that node.js handles the `rejectUnauthorized` setting. If the value is something that evaluates to false, such as undefined or null, certificate verification will be disabled. ## Recommendation Update to version 1.6.9 or later. If you are unable to upgrade, ensure all calls to socket.io to have a `rejectedUnauthorized: true` flag.
O3 Security · Impact-Aware SCA

Is GHSA-4r4m-hjwj-43p8 in your dependencies?

Find it across npm, including transitive dependencies.

Scan my dependencies How O3 SCA works
Insecure Defaults Allow MITM Over TLS in engine.io-client