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HIGH severity

multer vulnerable to Denial of Service via crafted multipart field namesGHSA-wc9g-mqfw-jrwm

HIGHFix: expressjs/multer@87a584e

GHSA-wc9g-mqfw-jrwm is a high-severity (CVSS 7.5) CWE-248 vulnerability in multer. A fix is available for multer — see the affected versions and patch details below.

Also known asCVE-2026-77078
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 12, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-wc9g-mqfw-jrwm.

EPSS Exploitation Probability

via FIRST.org ↗
0.5%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs40th percentile — riskier than 40% of all scored CVEsHighest risk
0.00%0.33%0.66%0.99%0.3%0.5%0.5%Sep 26Oct 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

GHSA-wc9g-mqfw-jrwm by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

7Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream
multernpm
23.0Mdownloads / week

Description

multer is a middleware for handling multipart/form-data in Node.js. A small multipart request containing two specially crafted text field names can cause an uncaught RangeError (Invalid array length) that terminates the Node.js process. The first field uses a very large numeric array index to allocate a maximum-length sparse array, and a second field then pushes past that length, which throws inside the append-field dependency and is not caught by multer. All versions before 2.3.0 are affected, and the issue is a remotely triggerable denial of service. The issue is fixed in multer 2.3.0. Upgrade to multer 2.3.0 to remediate.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
📦npmmulterall versions2.3.0npm install multer@2.3.0

Affected Products

1 product · 1 configurations
Application
multerexpressjs
< 2.3.0
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for multer, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update multer to 2.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-wc9g-mqfw-jrwm is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

This vulnerability affects multiple Red Hat products that bundle or use the multer npm package for handling multipart/form-data in Node.js applications. Products shipping multer versions below 2.3.0 are vulnerable to a remotely triggerable Denial of Service attack. An unauthenticated attacker can crash the Node.js…

Workaround published by Red Hat
Update affected products to versions containing multer 2.3.0 or later. There are no known workarounds - upgrading is the only remediation.
Source: Red Hat security advisory for GHSA-wc9g-mqfw-jrwm (CC BY 4.0)
ProductFixed inAdvisory
Red Hat Developer Hub 1.10rhdh/red-hat-developer-hub-backstage-plugin-lightspeed-backend:1791242697RHSA-2026:76788
Red Hat Developer Hub 1.10rhdh/rhdh-hub-rhel9:1791311495RHSA-2026:79088

Frequently Asked Questions

### Impact A vulnerability in multer allows a remote, unauthenticated attacker to crash the Node.js process with a single `multipart/form-data` request. Two specially crafted text field names cause an uncaught `RangeError: Invalid array length` inside multer's field parsing, which is not routed to the application error handler and terminates the process. All applications using multer to parse multipart requests are affected. ### Patches Users should upgrade to `2.3.0`. ### Workarounds None.
O3 Security · Impact-Aware SCA

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