CVE-2026-16221 (GCVE-0-2026-16221)

Vulnerability from cvelistv5 – Published: 2026-07-19 14:08 – Updated: 2026-07-20 13:53
VLAI
Title
fast-uri vulnerable to host confusion via literal backslash authority delimiter
Summary
Impact: fast-uri versions from 2.3.1 through 4.1.0 (including the 3.x line up to 3.1.3 and the 2.x line up to 2.4.2) do not treat a literal backslash character (U+005C) as an authority delimiter. Node's native WHATWG URL parser, used by fetch, undici, and Node's http and https clients, normalizes the backslash to a forward slash for special schemes such as http, https, ws, wss, ftp, and file. As a result, the two parsers extract different hosts from the same input string. Applications that use fast-uri to enforce host-based policy such as allowlists, denylists, loopback or SSRF filtering, redirect validation, or outbound proxy routing before passing the same URL into Node's URL or fetch consumers can be steered to an unintended destination, including cloud metadata endpoints, loopback, or internal hosts. Patches: upgrade to fast-uri 4.1.1, 3.1.4, or 2.4.3. Workarounds: none.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
SSVC
Exploitation: none Automatable: yes Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-07-20 13:53 UTC
CWE
  • CWE-436 - Interpretation Conflict
Assigner
References
Impacted products
Vendor Product Version CPE status
fast-uri fast-uri Affected: 2.3.1 , < 2.4.3 (semver)
Unaffected: 2.4.3 (semver)
Affected: 3.0.0 , < 3.1.4 (semver)
Unaffected: 3.1.4 (semver)
Affected: 4.0.0 , < 4.1.1 (semver)
Unaffected: 4.1.1 (semver)
guessed Create a notification for this product.
Credits
rampage0010 mcollina UlisesGascon
Show details on NVD website
To clipboard 

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