Denial of Service in multer Middleware for Node.js by Express.js

CVE-2026-77078

What is CVE-2026-77078?

The multer middleware used for handling multipart/form-data in Node.js applications has a vulnerability that can be exploited to trigger a denial of service (DoS). This occurs when a multipart request containing two specially crafted text field names is sent. The first field attempts to create an extremely large sparse array index, while the second field exceeds this length, leading to an uncaught RangeError that ultimately crashes the Node.js process. Versions before 2.3.0 are affected by this issue, which can be remotely triggered and poses a significant risk to applications relying on multer. The issue has been resolved in multer version 2.3.0, and it is highly recommended to upgrade to this version to mitigate potential attacks.

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