Host Confusion Affecting fast-uri package, versions >=2.4.5 <2.4.6>=3.1.6 <3.1.7>=4.1.3 <4.1.4
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JS-FASTURI-19502854
- published3 Sept 2026
- disclosed2 Sept 2026
- creditYashvant Mahadev Hange
Introduced: 2 Sep 2026
NewCVE-2026-84394 (opens in a new tab)How to fix?
Upgrade fast-uri to version 2.4.6, 3.1.7, 4.1.4 or higher.
Overview
fast-uri is a Dependency-free RFC 3986 URI toolbox
Affected versions of this package are vulnerable to Host Confusion in the parse() function, which returns a host that begins with [ but has no closing ], such as [@127.0.0.1, without validating it as an IPv6 literal or canonicalizing it as a domain name, leaving error undefined. An attacker can cause an application to make security decisions on a different host than HTTP clients resolve, defeating SSRF denylists, redirect allowlists, or proxy routing, by supplying a URL whose authority contains an unbalanced bracket. This affects applications that use the host from parse(), normalize(), equal(), or resolve() for access decisions while forwarding the original URL to an HTTP client.