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. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

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.

How does O3 Security protect against CVE-2023-31125?

O3 pinpoints whether CVE-2023-31125 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

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 67th 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.

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 April 10, 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

CVE-2023-31125

MEDIUM

Uncaught exception in engine.io

Also known asGHSA-q9mw-68c2-j6m5

Published

May 8, 2023

Updated

Apr 10, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

EPSS Exploitation Probability

via FIRST.org ↗

1.3%probability of exploitation in next 30 days

Lower Risk67th percentile+0.24%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Blast Radius

1 pkg affected

Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.

engine.ionpm

15.9Mdownloads / week

Description

Engine.IO is the implementation of transport-based cross-browser/cross-device bi-directional communication layer for Socket.IO. An uncaught exception vulnerability 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. A specially crafted HTTP request can trigger an uncaught exception on the Engine.IO server, thus killing the Node.js process. This impacts all the users of the engine.io package, including those who use depending packages like socket.io. This issue was fixed in version 6.4.2 of Engine.IO. There is no known workaround except upgrading to a safe version.

Affected Packages

1 total 1 fixed

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

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. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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.
How O3 protects you
O3 pinpoints whether CVE-2023-31125 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2023-31125. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

Engine.IO is the implementation of transport-based cross-browser/cross-device bi-directional communication layer for Socket.IO. An uncaught exception vulnerability 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. A specially crafted HTTP request can trigger an uncaught exception on the Engine.IO server, thus killing the Node.js process. This impacts all the users of the `engine.io` package, including those who use depending packages like `socket.io`. This issue was fixed in version 6.4.2 of Engine.IO. There is no

O3 Security · Impact-Aware SCA

Is CVE-2023-31125 in your dependencies?

O3 detects CVE-2023-31125 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works