CVE-2026-82333: Multer Denial of Service Vulnerability

HIGH
Advisory Identifier: GHSA-535w-7cp7-47q4
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CVSS 7.5
CWE-400
Published
Advisory Summary

CVE-2026-82333 is a HIGH (CVSS 7.5) denial of service vulnerability (CWE-400: Uncontrolled Resource Consumption) affecting Multer libraries in the npm ecosystem. The issue involves multer vulnerable to denial of service via oversized array index in field names. Remediation is available by upgrading affected packages to version 2.3.0.

CVE-2026-82333 at a Glance

CVE Identifier CVE-2026-82333
GHSA Identifier GHSA-535w-7cp7-47q4
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-400: Uncontrolled Resource Consumption
Affected Product Multer
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2026-82333

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: 2.3.0 
npm install multer@2.3.0
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-2026-82333, 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 2.3.0), 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-400: Uncontrolled Resource Consumption, where the product does not properly control the allocation and maintenance of a limited resource. 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 multer is vulnerable to a Denial of Service (DoS) via a crafted array index in multipart field names. The `append-field` dependency parses bracket notation in field names, and a large numeric index such as `items[4294967294]` forces allocation of a maximum-length sparse array. A following field with a non-numeric key on the same base then converts that array to an object by iterating its full length, which consumes CPU synchronously and leaves the process unable to handle other requests. A single HTTP request with a crafted multipart body is sufficient to exploit this, and it affects multer 1.x and 2.x. ### Patches Users should upgrade to `2.3.0` and configure `limits.fieldArrayIndexLimit` to the minimum array index their application requires. ### Workarounds None.

CVE-2026-82333 Affected Multer Versions

1 component(s)
Fixed Versions:
2.3.0
Product / Package Ecosystem Affected Versions Fixed Version
multer
npm/multer
npm
< 2.3.0
2.3.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/expressjs/multer/security/advisories/GHSA-535w-7cp7-47q4
NVD — CVE-2026-82333 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-82333
Multer Source Repository REPOSITORY
https://github.com/expressjs/multer/pull/1438
Security Fix Commit FIX COMMIT
https://github.com/expressjs/multer/commit/73c1759fa93b87366bc6dbd7abe1b80ddff7d27c
Multer Security Information SECURITY
https://cna.openjsf.org/security-advisories.html
Multer Source Repository REPOSITORY
https://github.com/expressjs/multer
Multer Release RELEASE
https://github.com/expressjs/multer/releases/tag/v2.3.0

Frequently Asked Questions

What is CVE-2026-82333?
CVE-2026-82333 is a security vulnerability in Multer involving multer vulnerable to Denial of Service via oversized array index in field names under CWE-400: Uncontrolled Resource Consumption.
Which Multer versions are affected?
Affected versions include releases prior to 2.3.0 across affected packages: multer.
What version fixes CVE-2026-82333?
Upgrading to 2.3.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is multer affected?
Yes, multer is affected in releases prior to 2.3.0. Upgrade your dependency to 2.3.0 or later.
What is the CVSS score of CVE-2026-82333?
CVE-2026-82333 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2026-82333?
CVE-2026-82333 is classified under CWE-400: Uncontrolled Resource Consumption (The product does not properly control the allocation and maintenance of a limited resource.).
How can I check npm dependencies for CVE-2026-82333?
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-535w-7cp7-47q4",
  "modified" : "2026-09-08T21:28:43Z",
  "published" : "2026-09-08T21:28:43Z",
  "aliases" : [ "CVE-2026-82333" ],
  "summary" : "multer vulnerable to Denial of Service via oversized array index in field names",
  "details" : "### Impact\n\nmulter is vulnerable to a Denial of Service (DoS) via a crafted array index in multipart field names. The `append-field` dependency parses bracket notation in field names, and a large numeric index such as `items[4294967294]` forces allocation of a maximum-length sparse array. A following field with a non-numeric key on the same base then converts that array to an object by iterating its full length, which consumes CPU synchronously and leaves the process unable to handle other requests. A single HTTP request with a crafted multipart body is sufficient to exploit this, and it affects multer 1.x and 2.x.\n\n### Patches\n\nUsers should upgrade to `2.3.0` and configure `limits.fieldArrayIndexLimit` to the minimum array index their application requires.\n\n### Workarounds\n\nNone.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "multer"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.3.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/expressjs/multer/security/advisories/GHSA-535w-7cp7-47q4"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-82333"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/expressjs/multer/pull/1438"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/expressjs/multer/commit/73c1759fa93b87366bc6dbd7abe1b80ddff7d27c"
  }, {
    "type" : "WEB",
    "url" : "https://cna.openjsf.org/security-advisories.html"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/expressjs/multer"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/expressjs/multer/releases/tag/v2.3.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-08T21:28:43Z",
    "nvd_published_at" : "2026-08-28T22:16:57Z"
  }
}