Summary
engine.io Uncaught Exception vulnerability
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.
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.
CVE-2023-31125 has a CVSS score of 6.5 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (6.4.2); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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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 |
Frequently Asked Questions
- What is CVE-2023-31125? CVE-2023-31125 is a medium-severity security vulnerability in engine.io (npm), affecting versions >= 5.1.0, < 6.4.2. It is fixed in 6.4.2.
- How severe is CVE-2023-31125? CVE-2023-31125 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of engine.io are affected by CVE-2023-31125? engine.io (npm) versions >= 5.1.0, < 6.4.2 is affected.
- Is there a fix for CVE-2023-31125? Yes. CVE-2023-31125 is fixed in 6.4.2. Upgrade to this version or later.
- Is CVE-2023-31125 exploitable, and should I be worried? Whether CVE-2023-31125 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2023-31125 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2023-31125? Upgrade
engine.ioto 6.4.2 or later.