CVE-2026-3520: Multer vulnerable to Denial of Service via uncontrolled recursion

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.7% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-04 · updated 2026-07-15
Weakness: CWE-674

Description

Multer is a node.js middleware for handling `multipart/form-data`. A vulnerability in Multer prior to version 2.1.1 allows an attacker to trigger a Denial of Service (DoS) by sending malformed requests, potentially causing stack overflow. Users should upgrade to version 2.1.1 to receive a patch. No known workarounds are available.

Affected products

multer: before 2.1.1 — fixed in 2.1.1

How to fix

Upgrade to a fixed version: multer 2.1.1. Check the vendor advisory for mitigations.

References

https://cna.openjsf.org/security-advisories.html
https://github.com/expressjs/multer/commit/7e66481f8b2e6c54b982b34c152479e096ce2752
https://github.com/expressjs/multer/security/advisories/GHSA-5528-5vmv-3xc2
https://www.cve.org/CVERecord?id=CVE-2026-3520
https://access.redhat.com/errata/RHSA-2026:6174
https://access.redhat.com/errata/RHSA-2026:6802
https://access.redhat.com/security/cve/CVE-2026-3520
https://bugzilla.redhat.com/show_bug.cgi?id=2444584
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-3520.json

Get alerted when CVE-2026-3520 or the next vulnerability affects your stack