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HIGH severity

CVE-2026-82333 — multer

HIGHFix: expressjs/multer#1438

CVE-2026-82333 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in multer. A fix is available for multer — see the affected versions and patch details below.

multer vulnerable to Denial of Service via oversized array index in field names

Also known asGHSA-535w-7cp7-47q4
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 22, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
0.5%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs41th percentile — riskier than 41% 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

CVE-2026-82333 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 394,803 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
12.9Mdownloads / week

Description

multer is a middleware for handling multipart/form-data in Node.js. A small multipart request with two specially crafted text field names can make multer's field parser synchronously iterate a maximum-length sparse array, blocking the event loop so the process cannot handle other requests. A large numeric array index in the first field allocates a maximum-length sparse array, and a second field with a non-numeric key then triggers a full-length iteration inside the append-field dependency. All versions before 2.3.0 are affected, and this is a remotely triggerable denial of service. multer 2.3.0 adds an opt-in fieldArrayIndexLimit option that rejects oversized array indexes. Upgrade to multer 2.3.0 and set limits.fieldArrayIndexLimit to the largest array index your application needs 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 CVE-2026-82333 is resolved across your whole dependency graph.

  3. Workarounds

    Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

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

Multiple vulnerabilities were found in multer, a Node.js middleware for handling multipart/form-data. CVE-2026-82333 allows a remote attacker to send specially crafted multipart requests with oversized array indices in field names, causing multer's field parser to allocate and iterate maximum-length sparse arrays.…

Workaround published by Red Hat
Upgrade to multer 2.3.0 or later. For CVE-2026-82333, multer 2.3.0 adds an opt-in fieldArrayIndexLimit option that rejects oversized array indexes - set limits.fieldArrayIndexLimit to the largest array index your application needs.
Source: Red Hat security advisory for CVE-2026-82333 (CC BY 4.0)
ProductFixed inAdvisory
Red Hat Ansible Automation Platform 2.2ansible-automation-platform/automation-portal:1792523640RHSA-2026:86675
Red Hat Ansible Automation Platform 2.2ansible-automation-platform/bootc-automation-portal-rhel9:1791865660RHSA-2026:82151
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 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 affec
O3 Security · Impact-Aware SCA

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CVE-2026-82333: multer DoS — Fixed in 2.3.0