Denial of Service in multer Middleware for Node.js by Express.js
CVE-2026-77078

7.5HIGH

Key Information:

Vendor

Multer

Status
Multer
Vendor
CVE Published:
28 August 2026

Badges

👾 Exploit Exists🟡 Public PoC

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.

Affected Version(s)

multer 0 < 2.3.0

multer 2.3.0

Exploit Proof of Concept (PoC)

PoC code is written by security researchers to demonstrate the vulnerability can be exploited. PoC code is also a key component for weaponization which could lead to ransomware.

CVE-2026-77078
Created by wtfkimi

References

https://github.com/expressjs/multer/security/advisories/G...
https://cna.openjsf.org/security-advisories.html

CVSS V3.1

Score:
7.5
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • 🟡

    Public PoC available

  • 👾

    Exploit known to exist

  • Vulnerability published

  • Vulnerability Reserved

Credit

O4FDev
UlisesGascon
.