CVE-2026-5079

What it is

Impact: multer versions 1.0.0 through 2.1.1 and 3.0.0-alpha.1 are vulnerable to a Denial of Service via deeply nested field names in multipart form data. The append-field dependency parses bracket notation in field names with no limit on nesting depth, allowing an attacker to force allocation of deeply nested object structures that consume CPU and memory. A single HTTP request with a crafted multipart body is sufficient to exploit this. Patches: Users should upgrade to multer 2.2.0 (2.x line) or 3.0.0-alpha.2 (3.x prerelease) and configure the new limits.fieldNestingDepth option to the minimum depth their application requires. Workarounds: Set limits.fields to a reasonable value to reduce the number of fields an attacker can send per request. This does not fully mitigate the issue but limits the impact.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of service disruption.

Exploit odds

0.3% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-06-15 14:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 10:58 UTC Last updatedMost recent change to the record

Details

Published

2026-06-15 14:16 UTC

Last modified

2026-06-17 10:58 UTC

Exploit probability

0.3% · EPSS, next 30 days

Weakness

CWE-400 · Uncontrolled resource consumption

Record status

Analyzed

Affected

• Expressjs Multer < 2.2.0
• Expressjs Multer 3.0.0

Attack profile CVSS 3.1 · 7.5

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High