Interpretation Conflict Affecting fast-uri package, versions >=2.3.1 <2.4.3>=3.0.0 <3.1.4>=4.0.0 <4.1.1
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-18021349
- published20 Jul 2026
- disclosed19 Jul 2026
- creditrampage0010
Introduced: 19 Jul 2026
NewCVE-2026-16221 (opens in a new tab)How to fix?
Upgrade fast-uri to version 2.4.3, 3.1.4, 4.1.1 or higher.
Overview
fast-uri is a Dependency-free RFC 3986 URI toolbox
Affected versions of this package are vulnerable to Interpretation Conflict via literal backslash handling in parseWithStatus in index.js. An attacker can bypass host-based validation by supplying a URI such as http://evil.com\@allowed.com, causing fast-uri to treat the input as an allowed host while Node’s WHATWG URL parser resolves it to a different destination. This breaks SSRF, redirect, and origin allowlist checks, letting requests be steered to unintended internal, loopback, or metadata endpoints.
Notes
- The mismatch matters anywhere the same URI string is parsed by
fast-urifor policy and then handed to Node consumers that use WHATWG parsing, includingfetch(),undici, and Nodehttp/httpsclients.