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multer vulnerable to Denial of Service via crafted multipart field names

High severity GitHub Reviewed Published Aug 28, 2026 in expressjs/multer • Updated Sep 8, 2026

Package

npm multer (npm)

Affected versions

< 2.3.0

Patched versions

2.3.0

Description

Impact

A vulnerability in multer allows a remote, unauthenticated attacker to crash the Node.js process with a single multipart/form-data request. Two specially crafted text field names cause an uncaught RangeError: Invalid array length inside multer's field parsing, which is not routed to the application error handler and terminates the process. All applications using multer to parse multipart requests are affected.

Patches

Users should upgrade to 2.3.0.

Workarounds

None.

References

@UlisesGascon UlisesGascon published to expressjs/multer Aug 28, 2026
Published by the National Vulnerability Database Aug 28, 2026
Published to the GitHub Advisory Database Sep 8, 2026
Reviewed Sep 8, 2026
Last updated Sep 8, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(21st percentile)

Weaknesses

Uncaught Exception

An exception is thrown from a function, but it is not caught. Learn more on MITRE.

CVE ID

CVE-2026-77078

GHSA ID

GHSA-wc9g-mqfw-jrwm

Source code

Credits

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