expressjs multer up to 2.4.x Asynchronous File Filter denial of service

Summaryinfo

A vulnerability was found in expressjs multer up to 2.4.x. It has been classified as problematic. The impacted element is an unknown function of the component Asynchronous File Filter. This manipulation causes denial of service. This vulnerability is handled as CVE-2026-113872. The attack can be initiated remotely. There is not any exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in expressjs multer up to 2.4.x. It has been declared as problematic. Affected by this vulnerability is an unknown code block of the component Asynchronous File Filter. The manipulation with an unknown input leads to a denial of service vulnerability. The CWE definition for the vulnerability is CWE-404. The product does not release or incorrectly releases a resource before it is made available for re-use. As an impact it is known to affect availability. The summary by CVE is:

multer is a middleware for Node.js that handles multipart/form-data file uploads. In versions from 2.0.0 before 2.5.0, when multer is configured with an asynchronous fileFilter, a single request can crash the Node.js process. If the request is aborted while one file's asynchronous fileFilter is still pending, the pending callback later resumes a parsing stream that multer has already torn down, and the underlying parser emits an error on a stream that no longer has an error listener, which Node raises as an unhandled error event so the process exits. Any application using multer with an asynchronous fileFilter is affected regardless of storage engine, while uploads using a synchronous fileFilter are not affected. The issue is fixed in multer 2.5.0, and users should upgrade to 2.5.0 or later. As a workaround, use a synchronous fileFilter.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-113872 since 10/20/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. The technical details are unknown and an exploit is not publicly available. The attack technique deployed by this issue is T1499 according to MITRE ATT&CK.

Upgrading to version 2.5.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-108188). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Vendor

• expressjs

Name

• multer

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4

Website

• Product: https://github.com/expressjs/multer/

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Be aware that VulDB is the high quality source for vulnerability data.

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