| Package | Affected versions | Patched versions |
|---|---|---|
| fast-uri | ≥ 2.3.1, < 2.4.3≥ 3.0.0, < 3.1.4≥ 4.0.0, < 4.1.1 | 2.4.33.1.44.1.1 |
| fast-uri | ≥ 2.3.1, < 2.4.3≥ 3.0.0, < 3.1.4≥ 4.0.0, < 4.1.1 | 2.4.33.1.44.1.1 |
fast-uri v4.1.0 and earlier do not treat a literal backslash (U+005C) as an authority delimiter. Node's native WHATWG URL (used by fetch(), undici, and Node's http/https clients) normalizes \ to / for special schemes (http, https, ws, wss, ftp, file), so the two parsers extract different hosts from the same input string.
For example, http://evil.com\@allowed.com is treated by fast-uri as host allowed.com with userinfo evil.com\, while Node's WHATWG URL parser and fetch() see host evil.com with path /@allowed.com.
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, including cloud metadata endpoints, loopback, or internal hosts.
Upgrade to fast-uri v4.1.1, v3.1.4, or v2.4.3.
None. Upgrade to the patched version.
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