CVE-2026-84394

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.

CVSS Metrics

• v3.1•HIGH•Score: 7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS Trends

Current EPSS score: 0.22%• Percentile: 13%

Techniques & Countermeasures

• CWE-436•Interpretation Conflict

  Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state.

Affected Systems

• debian•node-ajv

  all | all | < 8.20.0~ds+~cs7.1.5-1

• ubuntu•node-ajv

  all | all | all | all | all

• fast-uri•fast-uri

  ≥ 2.4.5, < 2.4.6 | ≥ 3.1.6, < 3.1.7 | ≥ 4.1.3, < 4.1.4

• openjsf•fast-uri

  2.4.5 | 3.1.6 | 4.1.3

References (5)

• https://github.com/fastify/fast-uri/security/advisories/GHSA-58mr-gqgx-xq4g
• https://cna.openjsf.org/security-advisories.html
• https://ubuntu.com/security/CVE-2026-84394
• https://www.cve.org/CVERecord?id=CVE-2026-84394
• https://security-tracker.debian.org/tracker/CVE-2026-84394