Denial of Service in Multer via Aborted Uploads

Executive Summary

CVE-2026-5038 is a vulnerability in the Multer library, which is used for handling multipart/form-data in Node.js applications. The issue occurs when using the diskStorage option, where aborted or malformed multipart uploads leave orphaned partial files on disk.

This happens because the Readable.pipe() call does not propagate the stream destroy signal to the underlying file system write stream (fs.WriteStream), causing incomplete cleanup of partial files.

An attacker can exploit this by triggering many aborted uploads, which causes disk space to be exhausted without requiring any application bugs.

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Impact Analysis

This vulnerability can lead to a Denial of Service (DoS) condition by exhausting the disk space on the server where the Multer library is used.

Since aborted or malformed uploads leave orphaned partial files, an attacker can fill up the disk by repeatedly triggering such uploads, potentially disrupting the availability of the affected application or service.

No special privileges or user interaction are required to exploit this vulnerability, making it easier for remote attackers to cause service disruption.

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Detection Guidance

This vulnerability causes orphaned partial files to accumulate on disk due to aborted or malformed multipart uploads when using multer's diskStorage. Detection can involve monitoring disk usage for unusual growth and checking for leftover partial upload files in the storage directories used by multer.

Specific commands to detect this issue might include checking disk space usage and listing files in the upload directory to identify orphaned partial files.

• Use disk space monitoring commands such as: df -h
• List files in the upload directory to find orphaned partial files, for example: ls -l /path/to/multer/uploads
• Use find to locate recently modified or partial files: find /path/to/multer/uploads -type f -mtime -1

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Mitigation Strategies

The primary mitigation step is to upgrade multer to a fixed version that addresses this vulnerability.

• Upgrade multer to version 2.2.0 or later in the 2.x line.
• Alternatively, upgrade to version 3.0.0-alpha.2 or later in the 3.x prerelease line.

There are no known workarounds other than upgrading to a patched version.

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Compliance Impact

This vulnerability causes a Denial of Service by exhausting disk space through orphaned partial files, impacting system availability.

While the CVE description and resources do not explicitly mention compliance with standards such as GDPR or HIPAA, the availability impact could indirectly affect compliance by disrupting service continuity or data processing operations.

There is no direct information provided about data confidentiality or integrity breaches, which are often critical for compliance with these regulations.

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