# CVE-2026-84394

## Summary

- **CVE ID:** CVE-2026-84394
- **Severity:** HIGH
- **CVSS Score:** 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N)
- **CWE:** CWE-436
- **Published:** Sep 2, 2026
- **Last Modified:** Sep 3, 2026

## Description

fast-uri accepts a host that contains an unbalanced or misplaced authority bracket without reporting an error. A host that starts with an opening bracket but does not end with a closing bracket is neither validated as an IP literal nor canonicalized as a domain name, so parse() returns it as the host with error undefined, while Node's URL and the HTTP clients built on it resolve the same string to a different host. An application that reads the parsed host to make a host decision, such as an SSRF denylist, a redirect allowlist, or proxy routing, and then passes the original URL to an HTTP client evaluates its policy against a string that is not the host the request reaches. The same host is carried through normalize, equal, and resolve. This affects fast-uri versions 2.4.5, 3.1.6, and 4.1.3, and is fixed in 2.4.6, 3.1.7, and 4.1.4, where parse() reports a malformed host for any host that contains a bracket but is not a valid IPv6 literal.

## Affected Products

- fast-uri — fast-uri (2.4.5)
- fast-uri — fast-uri (2.4.6)
- fast-uri — fast-uri (3.1.6)
- fast-uri — fast-uri (3.1.7)
- fast-uri — fast-uri (4.1.3)
- fast-uri — fast-uri (4.1.4)

## References

- [CNA](https://github.com/fastify/fast-uri/security/advisories/GHSA-58mr-gqgx-xq4g)
- [CNA](https://cna.openjsf.org/security-advisories.html)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.22%
- **EPSS Percentile:** 12.6

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._