How severe is CVE-2023-31125?

CVE-2023-31125 has a CVSS score of 6.5/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2023-31125?

CVE-2023-31125 affects the following packages: engine.io (npm). Ecosystems affected: npm.

How do I fix CVE-2023-31125?

Update engine.io to 6.4.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-31125 is resolved across your whole dependency graph.

How do I detect CVE-2023-31125 in my npm dependencies?

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

How do I mitigate CVE-2023-31125 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-2023-31125 actively exploited in the wild?

No public exploit code has been indexed for CVE-2023-31125 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-2023-31125?

CVE-2023-31125 has an EPSS (Exploit Prediction Scoring System) score of 1.3%, placing it in the 71th 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-2023-31125?

CVE-2023-31125 is classified as CWE-248 (CWE-248). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2023-31125 published, and has it been updated?

CVE-2023-31125 was published on May 8, 2023 and was last updated on October 28, 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-2023-31125 — engine.io

MEDIUMFix: socketio/engine.io@fc480b4

CVE-2023-31125 is a medium-severity (CVSS 6.5) CWE-248 vulnerability in engine.io. A fix is available for engine.io — see the affected versions and patch details below.

Uncaught exception in engine.io

Also known asGHSA-q9mw-68c2-j6m5

Published

May 8, 2023

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 6, 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 CVE-2023-31125.

EPSS Exploitation Probability

via FIRST.org ↗

1.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs71th percentile — riskier than 71% 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

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.

260other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

engine.ionpm

25.5Mdownloads / week

Description

Impact

A specially crafted HTTP request can trigger an uncaught exception on the Engine.IO server, thus killing the Node.js process.

TypeError: Cannot read properties of undefined (reading 'handlesUpgrades')
    at Server.onWebSocket (build/server.js:515:67)

This impacts all the users of the engine.io package, including those who uses depending packages like socket.io.

Patches

A fix has been released today (2023/05/02): 6.4.2

This bug was introduced in version 5.1.0 and included in version 4.1.0 of the socket.io parent package. Older versions are not impacted.

For socket.io users:

Version range	`engine.io` version	Needs minor update?
`[email protected]`	`~6.4.0`	`npm audit fix` should be sufficient
`[email protected]`	`~6.2.0`	Please upgrade to `[email protected]`
`[email protected]`	`~6.1.0`	Please upgrade to `[email protected]`
`[email protected]`	`~6.0.0`	Please upgrade to `[email protected]`
`[email protected]`	`~5.2.0`	Please upgrade to `[email protected]`
`[email protected]`	`~5.1.1`	Please upgrade to `[email protected]`
`[email protected]`	`~5.0.0`	Not impacted
`[email protected]`	`~4.1.0`	Not impacted
`[email protected]`	`~4.0.0`	Not impacted
`[email protected]`	`~3.6.0`	Not impacted
`[email protected]` and below	`~3.5.0`	Not impacted

Workarounds

There is no known workaround except upgrading to a safe version.

For more information

If you have any questions or comments about this advisory:

Open an issue in engine.io

Thanks to Thomas Rinsma from Codean for the responsible disclosure.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`engine.io`	≥ 5.1.0&&< 6.4.2	6.4.2`npm install engine.io@6.4.2`

Affected Products

1 product · 1 configurations

Application

engine.iosocket

≥ 5.1.0 && < 6.4.2

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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update engine.io to 6.4.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-31125 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

### Impact A specially crafted HTTP request can trigger an uncaught exception on the Engine.IO server, thus killing the Node.js process. ``` TypeError: Cannot read properties of undefined (reading 'handlesUpgrades') at Server.onWebSocket (build/server.js:515:67) ``` This impacts all the users of the [`engine.io`](https://www.npmjs.com/package/engine.io) package, including those who uses depending packages like [`socket.io`](https://www.npmjs.com/package/socket.io). ### Patches A fix has been released today (2023/05/02): [6.4.2](https://github.com/socketio/engine.io/releases/tag/6.4.2)