UAParser.js: Unbounded `Sec-CH-UA-Model` parsing can trigger ReDoS in `withClientHints()`
Summary
A regular expression denial-of-service (ReDoS) vulnerability has been discovered in ua-parser-js when using the Client Hints API. By sending a crafted Sec-CH-UA-Model header to an application that calls UAParser(headers).withClientHints(), an attacker can cause the parser to spend excessive CPU time due to catastrophic backtracking in the device regex:
/ ([\w ]+) miui\/v?\d/iUnlike when using the User-Agent value, which has a hard limit of UA_MAX_LENGTH = 500, when using Client Hints, values are copied without a length limit before being passed into regex parsing.
PoC
const { UAParser } = require('ua-parser-js');
const headers = {
'sec-ch-ua-platform': '"Android"',
'sec-ch-ua-mobile': '?1',
'sec-ch-ua-model': '"' + 'A '.repeat(25000) + '"'
};
const t0 = process.hrtime.bigint();
UAParser(headers).withClientHints();
const ms = Number(process.hrtime.bigint() - t0) / 1e6;
if (ms > 100) {
console.log('Potential ReDoS');
}Impact
This vulnerability allows an unauthenticated attacker to trigger a denial-of-service condition in any server-side application that uses UAParser(headers).withClientHints(). A single request with a ~32,000-character model value can consume over 400ms of CPU time, with parsing time growing polynomially with input length. The impact is availability only, there is no confidentiality or integrity impact.
Affected Versions
ua-parser-js versions >=2.0.1, <=2.0.9 are affected. The withClientHints() API is not present in version 0.7.x or 1.x.
Patches
A patch has been released to fix the vulnerable regular expression and limit the Client Hints input. Users should update to version 2.0.10 or later.
References
Credits
Thanks to @sondt99, who first reported the issue.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | ua-parser-js | >= 2.0.1, < 2.0.10 | 2.0.10 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L- Weakness (CWE)
CWE-1333, CWE-400- Platform
- npm
- Package
ua-parser-js- Disclosed
- 15.06.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-9h5v-pfqq-x599 - CC BY 4.0
Vulnerability history: ua-parser-js
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 6
- First → latest
- 05.2021 06.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 5
- Medium 1
Disclosures per year
- 2021: 3
- 2022: 1
- 2023: 1
- 2024: 0
- 2025: 0
- 2026: 1
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UAParser.js: Unbounded `Sec-CH-UA-Model` parsing can trigger ReDoS in `withClientHints()` this entry
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