CVE-2026-77063: Multer Multer Vulnerable To File Size Vulnerability

LOW
Advisory Identifier: GHSA-qvfw-j98x-7q72
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CVSS 3.7
CWE-362
Published
Advisory Summary

CVE-2026-77063 is a LOW (CVSS 3.7) multer vulnerable to file size vulnerability (CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')) affecting Multer libraries in the npm ecosystem. The issue involves multer vulnerable to file size limit bypass via async filefilter race condition. Remediation is available by upgrading affected packages to version 2.3.0.

CVE-2026-77063 at a Glance

CVE Identifier CVE-2026-77063
GHSA Identifier GHSA-qvfw-j98x-7q72
Severity LOW
CVSS v3.1 Base Score 3.7
CWE Classification CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
Affected Product Multer
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 3.7

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

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

How to Fix CVE-2026-77063

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-2026-77063, 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-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition'), where the product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently. 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 When `multer` is configured with an asynchronous `fileFilter`, the `limits.fileSize` limit can be bypassed. The `'limit'` event is registered inside the async `fileFilter` callback, so if a file exceeds `limits.fileSize` before that callback runs, the event is missed and the oversized upload is accepted instead of being rejected with a `LIMIT_FILE_SIZE` error. Applications that rely on `limits.fileSize` to reject oversized uploads are affected on all upload methods (`.single()`, `.array()`, `.fields()`, `.any()`). Uploads using a synchronous `fileFilter` are not affected. ### Patches Users should upgrade to `2.3.0`. ### Workarounds Use a synchronous `fileFilter`, or validate the uploaded file size after the upload completes.

CVE-2026-77063 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-qvfw-j98x-7q72
NVD — CVE-2026-77063 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-77063
Security Fix Commit FIX COMMIT
https://github.com/expressjs/multer/commit/ab6aeae650328cf31799dcfa4c3e116ba8faaacc
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-2026-77063?
CVE-2026-77063 is a security vulnerability in Multer involving multer vulnerable to file size limit bypass via async fileFilter race condition under CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition').
Which Multer versions are affected?
Affected versions include releases prior to 2.3.0 across affected packages: multer.
What version fixes CVE-2026-77063?
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-2026-77063?
CVE-2026-77063 has a CVSS v3.1 base score of 3.7 (LOW) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N.
What CWE is associated with CVE-2026-77063?
CVE-2026-77063 is classified under CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') (The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.).
How can I check npm dependencies for CVE-2026-77063?
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-qvfw-j98x-7q72",
  "modified" : "2026-09-08T21:29:42Z",
  "published" : "2026-09-08T21:29:42Z",
  "aliases" : [ "CVE-2026-77063" ],
  "summary" : "multer vulnerable to file size limit bypass via async fileFilter race condition",
  "details" : "### Impact\n\nWhen `multer` is configured with an asynchronous `fileFilter`, the `limits.fileSize` limit can be bypassed. The `'limit'` event is registered inside the async `fileFilter` callback, so if a file exceeds `limits.fileSize` before that callback runs, the event is missed and the oversized upload is accepted instead of being rejected with a `LIMIT_FILE_SIZE` error. Applications that rely on `limits.fileSize` to reject oversized uploads are affected on all upload methods (`.single()`, `.array()`, `.fields()`, `.any()`). Uploads using a synchronous `fileFilter` are not affected.\n\n### Patches\n\nUsers should upgrade to `2.3.0`.\n\n### Workarounds\n\nUse a synchronous `fileFilter`, or validate the uploaded file size after the upload completes.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N"
  } ],
  "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-qvfw-j98x-7q72"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-77063"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/expressjs/multer/commit/ab6aeae650328cf31799dcfa4c3e116ba8faaacc"
  }, {
    "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-362" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-08T21:29:42Z",
    "nvd_published_at" : "2026-08-28T22:16:53Z"
  }
}