CVE-2026-3520: Multer Denial of Service Vulnerability

HIGH
Advisory Identifier: GHSA-5528-5vmv-3xc2
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CWE-674
Published
Advisory Summary

CVE-2026-3520 is a HIGH denial of service vulnerability (CWE-674: Uncontrolled Recursion) affecting Multer libraries in the npm ecosystem. The issue involves multer vulnerable to denial of service via uncontrolled recursion. Remediation is available by upgrading affected packages to version 2.1.1.

CVE-2026-3520 at a Glance

CVE Identifier CVE-2026-3520
GHSA Identifier GHSA-5528-5vmv-3xc2
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-674: Uncontrolled Recursion
Affected Product Multer
Package Ecosystem npm
Published Date
Last Updated

How to Fix CVE-2026-3520

To remediate this vulnerability, upgrade all affected Multer dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

multer fixed: 2.1.1 
npm install multer@2.1.1
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls multer

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-3520, inspect your project dependencies using npm:

npm ls multer

Analyze the terminal output to locate any version of Multer in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.1.1), your application is affected.

Note: The npm ls multer command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-674: Uncontrolled Recursion, where the product does not properly control the amount of recursion that takes place, consuming excessive resources, such as allocated memory or the program stack. In Multer, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact A vulnerability in Multer versions < 2.1.1 allows an attacker to trigger a Denial of Service (DoS) by sending malformed requests, potentially causing stack overflow. ### Patches Users should upgrade to `2.1.1` ### Workarounds None ### Resources - https://github.com/expressjs/multer/security/advisories/GHSA-5528-5vmv-3xc2 - https://www.cve.org/CVERecord?id=CVE-2026-3520 - https://github.com/expressjs/multer/commit/7e66481f8b2e6c54b982b34c152479e096ce2752 - https://cna.openjsf.org/security-advisories.html

CVE-2026-3520 Affected Multer Versions

1 component(s)
Fixed Versions:
2.1.1
Product / Package Ecosystem Affected Versions Fixed Version
multer
npm/multer
npm
< 2.1.1
2.1.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/expressjs/multer/security/advisories/GHSA-5528-5vmv-3xc2
NVD — CVE-2026-3520 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-3520
Security Fix Commit FIX COMMIT
https://github.com/expressjs/multer/commit/7e66481f8b2e6c54b982b34c152479e096ce2752
Multer Security Information SECURITY
https://cna.openjsf.org/security-advisories.html
Multer Source Repository REPOSITORY
https://github.com/expressjs/multer
CVE Official Record — CVE-2026-3520 CVE
https://www.cve.org/CVERecord?id=CVE-2026-3520

Frequently Asked Questions

What is CVE-2026-3520?
CVE-2026-3520 is a security vulnerability in Multer involving Multer Vulnerable to Denial of Service via Uncontrolled Recursion under CWE-674: Uncontrolled Recursion.
Which Multer versions are affected?
Affected versions include releases prior to 2.1.1 across affected packages: multer.
What version fixes CVE-2026-3520?
Upgrading to 2.1.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is multer affected?
Yes, multer is affected in releases prior to 2.1.1. Upgrade your dependency to 2.1.1 or later.
What CWE is associated with CVE-2026-3520?
CVE-2026-3520 is classified under CWE-674: Uncontrolled Recursion (The product does not properly control the amount of recursion that takes place, consuming excessive resources, such as allocated memory or the program stack.).
How can I check npm dependencies for CVE-2026-3520?
Run the dependency tree command: 'npm ls multer'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5528-5vmv-3xc2",
  "modified" : "2026-03-05T00:27:50Z",
  "published" : "2026-03-05T00:27:50Z",
  "aliases" : [ "CVE-2026-3520" ],
  "summary" : "Multer Vulnerable to Denial of Service via Uncontrolled Recursion",
  "details" : "### Impact\n\nA vulnerability in Multer versions < 2.1.1 allows an attacker to trigger a Denial of Service (DoS) by sending malformed requests, potentially causing stack overflow.\n\n### Patches\n\nUsers should upgrade to `2.1.1`\n\n### Workarounds\n\nNone\n\n### Resources\n\n- https://github.com/expressjs/multer/security/advisories/GHSA-5528-5vmv-3xc2\n- https://www.cve.org/CVERecord?id=CVE-2026-3520\n- https://github.com/expressjs/multer/commit/7e66481f8b2e6c54b982b34c152479e096ce2752\n- https://cna.openjsf.org/security-advisories.html",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "multer"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.1.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/expressjs/multer/security/advisories/GHSA-5528-5vmv-3xc2"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-3520"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/expressjs/multer/commit/7e66481f8b2e6c54b982b34c152479e096ce2752"
  }, {
    "type" : "WEB",
    "url" : "https://cna.openjsf.org/security-advisories.html"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/expressjs/multer"
  }, {
    "type" : "WEB",
    "url" : "https://www.cve.org/CVERecord?id=CVE-2026-3520"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-674" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-05T00:27:50Z",
    "nvd_published_at" : "2026-03-04T17:16:22Z"
  }
}