How severe is CVE-2016-10536?

CVE-2016-10536 has a CVSS score of 5.9/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2016-10536?

CVE-2016-10536 affects the following packages: engine.io-client (npm). Ecosystems affected: npm.

How do I fix CVE-2016-10536?

Update engine.io-client to 1.6.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2016-10536 is resolved across your whole dependency graph.

How do I detect CVE-2016-10536 in my npm dependencies?

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.

How do I mitigate CVE-2016-10536 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 CVE-2016-10536 actively exploited in the wild?

No public exploit code has been indexed for CVE-2016-10536 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 CVE-2016-10536?

CVE-2016-10536 has an EPSS (Exploit Prediction Scoring System) score of 1.0%, placing it in the 62th 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 CVE-2016-10536?

CVE-2016-10536 is classified as CWE-300 (CWE-300), CWE-295 (CWE-295). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2016-10536 published, and has it been updated?

CVE-2016-10536 was published on May 31, 2018 and was last updated on July 8, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

MEDIUM severity

CVE-2016-10536 — engine.io-client

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

CVE-2016-10536 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.

Insecure Defaults Allow MITM Over TLS in engine.io-client

Also known asGHSA-4r4m-hjwj-43p8

Published

May 31, 2018

Updated

Jul 8, 2026

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

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

How urgent is this, really

CVE-2016-10536 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

Ecosystem	Package	Vulnerable range	Fix
📦npm	`engine.io-client`	all versions	1.6.9`npm 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

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.
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 CVE-2016-10536 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.

Frequently Asked Questions

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`,

O3 Security · Impact-Aware SCA

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CVSS Score

5.9/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

Raw vector

CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

CWE Classification

CWE-300CWE-300 CWE-295CWE-295

Weaponization

No known public exploit tooling found.

OpenSSF Scorecard

Package health score

engine.io-client

1.8/10

Code-Review0/10

Maintained0/10

Branch-ProtectionN/A

Assessed Oct 5, 2026

Timeline

Disclosed

May 31, 2018

Last updated

Jul 8, 2026

Identifiers

CVE-2016-10536

GHSA-4r4m-hjwj-43p8

References

Advisorynodesecurity.io Advisorycigital.com Advisorynvd.nist.gov Advisorygithub.com Fixgithub.com Webcigital.com Webnpmjs.com

Related vulnerabilities

This CVE is medium severity; 8 of 8 other CVEs with CWE-300 are rated as high or higher (top: critical).

CVE-2024-39705CVE-2024-31206GHSA-j3rq-4xjw-xg63CVE-2019-16546CVE-2020-10749CVE-2020-2185CVE-2009-3555CVE-2016-1000224Browse all CWE-300

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedJul 8, 2026

CVE-2016-10536 — engine.io-client

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2016-10536 in your dependencies?