🛡️ CVE-2026-48125 — ua-parser-js

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](https://github.com/faisalman/ua-parser-js/blob/2.0.9/src/main/ua-parser.js#L615):

```js

/ ([\w ]+) miui\/v?\d/i

```

Unlike 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

```js

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

• [Regular expression Denial of Service - ReDoS (OWASP)](https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS)

Credits

Thanks to [@sondt99](https://github.com/sondt99), who first reported the issue.