# CVE-2026-5079: OpenJS Multer Denial of Service via deeply nested field names

Source: https://junglewise.ai/threats/cve-2026-5079-openjs-multer-denial-of-service-via-deeply-nested-field-names  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-15. Updated: 2026-06-17  
License: CC BY 4.0 with a link back

CVE-2026-5079 · Severity: high · CVSS 7.5 · Published 2026-06-15

Multer, a popular middleware for handling file uploads in web applications, is vulnerable to a Denial of Service (DoS) attack. An attacker can send a specially crafted request with deeply nested field names to exhaust the server's CPU and memory resources. This can lead to application crashes or significant performance degradation, preventing legitimate users from accessing the service.

Technologies: [multer (npm)](https://junglewise.ai/threats/technologies/npm-multer), [OpenJS Foundation Multer](https://junglewise.ai/threats/technologies/multer). Vendors: [npm](https://junglewise.ai/threats/vendors/npm), [OpenJS Foundation](https://junglewise.ai/threats/vendors/openjs-foundation).

## Quick answers

**Is CVE-2026-5079 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-5079 being exploited in the wild.

**How severe is CVE-2026-5079?** High severity, with a CVSS score of 7.5, published 15 June 2026.

**Which products and versions are affected?** multer (npm) SEMVER:introduced=1.0.0,fixed=2.2.0; OpenJS Foundation Multer >= 1.0.0, < 2.2.0; >= 3.0.0-alpha.1, < 3.0.0-alpha.2.

**Is there a fix for CVE-2026-5079?** Yes. multer (npm): upgrade to 2.2.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-5079 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-5079?** Check whether you run multer (npm) or OpenJS Foundation Multer at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- multer (npm): upgrade to 2.2.0 or later

  ```sh
  npm install multer@2.2.0
  ```


## Technical details

Multer is vulnerable to Uncontrolled Resource Consumption (CWE-400) due to how its dependency, `append-field`, handles bracket notation in multipart form field names (e.g., `a[b][c]`). The parser does not enforce a limit on nesting depth, allowing a remote, unauthenticated attacker to submit a single HTTP request that forces the server to allocate deeply nested object structures. This process consumes excessive CPU and memory, leading to a Denial of Service. The issue is resolved in version 2.2.0, which introduces the `limits.fieldNestingDepth` configuration option.

## Affected products

- expressjs multer >= 1.0.0, < 2.2.0; >= 3.0.0-alpha.1, < 3.0.0-alpha.2

## Identifiers

- CVE-2026-5079
- GHSA-72gw-mp4g-v24j

## Timeline

- 2026-06-15: disclosed
- 2026-06-17: advisory
- 2026-06-17: patched: Fixed in version 2.2.0 and 3.0.0-alpha.2

## References

- [https://api.github.com/users/tndud042713](https://api.github.com/users/tndud042713)
- [https://github.com/tndud042713](https://github.com/tndud042713)
- [https://api.github.com/users/tndud042713/gists%7B/gist_id%7D](https://api.github.com/users/tndud042713/gists%7B/gist_id%7D)
- [https://api.github.com/users/tndud042713/repos](https://api.github.com/users/tndud042713/repos)
- [https://avatars.githubusercontent.com/u/70098543?v=4](https://avatars.githubusercontent.com/u/70098543?v=4)
- [https://api.github.com/users/tndud042713/events%7B/privacy%7D](https://api.github.com/users/tndud042713/events%7B/privacy%7D)

## Related threats

- [multer denial of service in asynchronous fileFilter after request teardown](https://junglewise.ai/threats/cve-2026-113872-multer-is-a-middleware-for-node-js-that-handles-multipart-form)
- [Express multer Denial of Service via orphaned disk writes](https://junglewise.ai/threats/cve-2026-88932-express-multer-denial-of-service-via-orphaned-disk-writes)
- [multer denial of service via oversized array index](https://junglewise.ai/threats/cve-2026-82333-multer-denial-of-service-via-oversized-array-index-in-field-names)
- [multer Denial of Service via crafted multipart field names](https://junglewise.ai/threats/cve-2026-77078-multer-denial-of-service-via-crafted-multipart-field-names)
- [multer file size limit bypass via async fileFilter race condition](https://junglewise.ai/threats/cve-2026-77063-multer-file-size-limit-bypass-via-async-filefilter-race-condition)