CVE-2026-82333 multer vulnerable to Denial of Service via oversized array index in field names

High 7.5 Published 28 Aug 2026 Updated 31 Aug 2026

Attackers can cause denial of service in Node.js applications using multer by sending crafted multipart requests that block the event loop.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2026-82333?

CVE-2026-82333 is a high-severity denial of service vulnerability in multer, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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.

Weakness: CWE-400

Which versions are affected by CVE-2026-82333?

2 open source packages ship an affected version, including multer. It affects 1 product.

Package	Affected	Fixed in
`multer` npm	All versions	`2.3.0`
`multer` npm	All versions	`2.3.0`

Products include Expressjs Multer.

How do I fix CVE-2026-82333?

Upgrade multer to 2.3.0 or later.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-82333 being exploited?

There is no known exploitation of CVE-2026-82333 in the wild and no public exploit code.

Sources

Also known as CLEANSTART-2026-RK66393, CLSA-2026-1790609063, ECHO-39b2-3209-49fe, GHSA-535w-7cp7-47q4, MINI-65vv-vh5c-9v3j, MINI-9339-w9fg-2xwq and 2 more.