engine.io Uncaught Exception vulnerability
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? |
|---|---|---|
socket.io@4.6.x |
~6.4.0 |
npm audit fix should be sufficient |
socket.io@4.5.x |
~6.2.0 |
Please upgrade to socket.io@4.6.x |
socket.io@4.4.x |
~6.1.0 |
Please upgrade to socket.io@4.6.x |
socket.io@4.3.x |
~6.0.0 |
Please upgrade to socket.io@4.6.x |
socket.io@4.2.x |
~5.2.0 |
Please upgrade to socket.io@4.6.x |
socket.io@4.1.x |
~5.1.1 |
Please upgrade to socket.io@4.6.x |
socket.io@4.0.x |
~5.0.0 |
Not impacted |
socket.io@3.1.x |
~4.1.0 |
Not impacted |
socket.io@3.0.x |
~4.0.0 |
Not impacted |
socket.io@2.5.0 |
~3.6.0 |
Not impacted |
socket.io@2.4.x 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 software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | engine.io | >= 5.1.0, < 6.4.2 | 6.4.2 |
References
- https://github.com/socketio/engine.io/security/advisories/GHSA-q9mw-68c2-j6m5
- https://nvd.nist.gov/vuln/detail/CVE-2023-31125
- https://github.com/socketio/engine.io/commit/fc480b4f305e16fe5972cf337d055e598372dc44
- https://github.com/socketio/engine.io
- https://github.com/socketio/engine.io/releases/tag/6.4.2
- https://security.netapp.com/advisory/ntap-20230622-0002
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-248- Platform
- npm
- Package
engine.io- Disclosed
- 03.05.2023
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-q9mw-68c2-j6m5 - CC BY 4.0
Vulnerability history: engine.io
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 7
- First → latest
- 01.2022 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 5
- Medium 2
Disclosures per year
- 2022: 3
- 2023: 1
- 2024: 0
- 2025: 0
- 2026: 3
-
engine.io Uncaught Exception vulnerability this entry
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