# CVE-2026-31808: Sindresorhus file-type infinite loop in ASF parser

Source: https://junglewise.ai/threats/cve-2026-31808-sindresorhus-file-type-infinite-loop-in-asf-parser  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-03-10. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-31808 · Severity: low · CVSS 3.1 · Published 2026-03-10

The file-type npm package, which detects file types by analyzing file signatures, contains a denial-of-service vulnerability in its ASF (WMV/WMA) file format parser. When processing specially crafted malformed files, an attacker can trigger an infinite loop that freezes the entire Node.js application with just a 55-byte payload. This impacts any application using file-type to process untrusted user-supplied files.

Technologies: [file-type (npm)](https://junglewise.ai/threats/technologies/file-type). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-31808 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-31808 being exploited in the wild.

**How severe is CVE-2026-31808?** Low severity, with a CVSS score of 3.1, published 10 March 2026.

**Which products and versions are affected?** file-type (npm) SEMVER:introduced=13.0.0,fixed=21.3.1.

**Is there a fix for CVE-2026-31808?** Yes. file-type (npm): upgrade to 21.3.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-31808 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-31808?** Check whether you run file-type (npm) 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

- file-type (npm): upgrade to 21.3.1 or later

  ```sh
  npm install file-type@21.3.1
  ```


## Technical details

The vulnerability is a CWE-835 infinite loop condition in the ASF parser component of file-type. When parsing an ASF sub-header with a size field of zero, the payload calculation results in a negative value (-24), causing tokenizer.ignore(payload) to move the read position backwards instead of forwards. This causes the parser to re-read the same malformed sub-header indefinitely, starving the Node.js event loop. The vulnerability affects versions 13.0.0 through 21.3.0 of the npm file-type package. No authentication or privileges are required; an attacker only needs to provide a crafted 55-byte input file to a vulnerable application. The issue is fixed in version 21.3.1 via commit 319abf8. Workarounds include validating input buffer sizes or running file-type detection in a separate worker thread with a timeout.

## Affected products

- Sindresorhus file-type >=13.0.0, <21.3.1

## Identifiers

- CVE-2026-31808
- GHSA-5v7r-6r5c-r473

## Timeline

- 2026-03-10: disclosed: Vulnerability published on GitHub Advisory Database and OSV
- 2026-03-10: patched: Fixed in version 21.3.1 with commit 319abf8

## References

- [https://github.com/sindresorhus/file-type/security/advisories/GHSA-5v7r-6r5c-r473](https://github.com/sindresorhus/file-type/security/advisories/GHSA-5v7r-6r5c-r473)
- [https://github.com/sindresorhus/file-type/commit/319abf871b50ba2fa221b4a7050059f1ae096f4f](https://github.com/sindresorhus/file-type/commit/319abf871b50ba2fa221b4a7050059f1ae096f4f)
- [https://github.com/sindresorhus/file-type](https://github.com/sindresorhus/file-type)

## Related threats

- [file-type ZIP decompression bomb DoS via [Content_Types].xml](https://junglewise.ai/threats/cve-2026-32630-file-type-zip-decompression-bomb-dos-via-content-types-xml)
- [file-type infinite loop via malformed MKV file](https://junglewise.ai/threats/cve-2022-36313-file-type-infinite-loop-via-malformed-mkv-file)