GHSA-7p8r-x3mc-p8w7
fast-uri vulnerable to host confusion via backslash authority introducer
Quick fix
GHSA-7p8r-x3mc-p8w7 — fast-uri: upgrade to the fixed version with the command below.
npm install fast-uri@2.4.4 Details
### Impact
`fast-uri` v4.1.1 and earlier require a literal `//` to recognize a URI authority, so a reference that uses `\\`, `/\`, or `\/` as the authority introducer (in place of `//`, after an optional scheme) is parsed with no authority: the sequence and everything after it fold into the path. Node's native WHATWG `URL` (used by `fetch()`, `undici`, and Node's `http`/`https` clients) instead treats `\` as interchangeable with `/` for special schemes (`http`, `https`, `ws`, `wss`, `ftp`, `file`), so the two parsers extract different hosts from the same input.
For example, `fast-uri` resolves `\\evil.com/path` against base `https://allowed.com/` to `https://allowed.com/%5C%5Cevil.com/path` (confined to the trusted host), while Node's WHATWG URL resolves the same reference to `https://evil.com/path`.
Applications that use `fast-uri` to enforce host-based policy (allowlists, denylists, loopback/SSRF filtering, redirect validation, outbound proxy routing) before passing the same URL into Node's URL or `fetch()` consumers see a policy/use desync and can be steered to an unintended destination.
### Patches
Upgrade to `fast-uri` v4.1.2, v3.1.5, v2.4.4.
### Workarounds
None. Upgrade to the patched version.
Are you affected?
Enter the version of the package you're using.
Affected packages
References
- https://github.com/fastify/fast-uri/security/advisories/GHSA-7p8r-x3mc-p8w7 [WEB]
- https://nvd.nist.gov/vuln/detail/CVE-2026-18446 [ADVISORY]
- https://github.com/fastify/fast-uri/commit/f3c6c905f47831007490f466c5945012e905cc52 [WEB]
- https://cna.openjsf.org/security-advisories.html [WEB]
- https://github.com/fastify/fast-uri [PACKAGE]
- https://github.com/fastify/fast-uri/releases/tag/v4.1.2 [WEB]