Vulnerability Description
fast-uri before 4.1.2, 3.1.5, and 2.4.4 requires a literal double forward slash to recognize a URI authority, so a reference that uses a backslash based introducer in place of it (backslash backslash, forward slash backslash, or backslash forward slash) is parsed with no authority and folds into the path. Node's native WHATWG URL parser instead treats a backslash as interchangeable with a forward slash for special schemes, so the two parsers extract different hosts from the same input. Applications that use fast-uri to enforce host based policy such as allowlists, SSRF filtering, or redirect validation before passing the same URL into Node's URL or fetch consumers can be steered to an unintended host. Upgrade to fast-uri 4.1.2, 3.1.5, or 2.4.4.
CVSS Score
HIGH
Related Weaknesses (CWE)
References
- https://cna.openjsf.org/security-advisories.html
- https://github.com/fastify/fast-uri/security/advisories/GHSA-7p8r-x3mc-p8w7
FAQ
What is CVE-2026-18446?
CVE-2026-18446 is a vulnerability with a CVSS score of 7.5 (HIGH). fast-uri before 4.1.2, 3.1.5, and 2.4.4 requires a literal double forward slash to recognize a URI authority, so a reference that uses a backslash based introducer in place of it (backslash backslash,...
How severe is CVE-2026-18446?
CVE-2026-18446 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-18446?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.