CVE-2023-31125: engine.io Uncaught Exception vulnerability
Summary
CVE-2023-31125: engine.io Uncaught Exception vulnerability. Affects engine.io versions >= 5.1.0, < 6.4.2. Fixed in 6.4.2. How to fix ↓
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Background
The engine.io package is an open-source library that provides real-time bidirectional communication between web clients and servers. It is commonly used by applications that require real-time updates, such as chat applications and collaborative tools. This vulnerability affects all users of the engine.io package, including those who use depending packages like socket.io.
Vulnerability Detail
A specially crafted HTTP request can trigger an uncaught exception on the Engine.IO server, leading to the termination of the Node.js process. The exception is caused by a TypeError when attempting to read properties of an undefined object (handlesUpgrades). This vulnerability can be exploited by an attacker to disrupt the availability of the affected application. The vulnerability was introduced in version 5.1.0 of the engine.io package and fixed in version 6.4.2. Users of the socket.io package should also update to a safe version.
How To Fix
Latest published version: 6.6.11 as of 23 Oct 2026
npm install engine.io@6.6.11Upgrading to it may include breaking changes; the version below is the minimum fixed release for this vulnerability.
If you need the minimum change
6.4.2
This is the first release that contains the fix.
npm install engine.io@6.4.2Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
There is no known workaround for this vulnerability except upgrading to a safe version.
Conclusion
The engine.io Uncaught Exception vulnerability can be mitigated by upgrading to version 6.4.2 of the engine.io package. Users of the socket.io package should also ensure they are using a safe version. For further support on vulnerability remediation, please contact DevNack.com.
See every vulnerability recorded for engine.io →
FAQ
This vulnerability can be exploited by an attacker to terminate the Node.js process, leading to the unavailability of the affected application.
Versions 5.1.0 to 6.4.1 of the engine.io package are affected.
No, there are no known workarounds for this vulnerability.
You can use the Vulert Playground at Vulert Scanner to check if your application is affected by this vulnerability. Simply upload your package-lock.json file and the Vulert Playground will provide real-time alerts for open-source vulnerabilities.
You can open an issue in the engine.io GitHub repository for more information.
References
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