Vulnerability · Published Sep 2, 2026 · Assigned by openjs
CVE-2026-84394fast-uri vulnerable to host confusion via an unclosed bracket in the URI authority
High 7.5
In plain English
A high-severity security flaw in fast-uri from fast-uri. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 32% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:13 | node-ajv | no fix listed | DEBIAN-CVE-2026-84394 |
| Debian:14 | node-ajv | 8.20.0~ds+~cs7.1.5-1 | DEBIAN-CVE-2026-84394 |
| Ubuntu:22.04:LTS | node-ajv | no fix listed | UBUNTU-CVE-2026-84394 |
| Ubuntu:24.04:LTS | node-ajv | no fix listed | UBUNTU-CVE-2026-84394 |
| Ubuntu:26.04:LTS | node-ajv | no fix listed | UBUNTU-CVE-2026-84394 |
| Ubuntu:26.10 | node-ajv | no fix listed | UBUNTU-CVE-2026-84394 |
| npm | fast-uri | 2.4.6 | GHSA-58mr-gqgx-xq4g |
| npm | fast-uri | 3.1.7 | GHSA-58mr-gqgx-xq4g |
| npm | fast-uri | 4.1.4 | GHSA-58mr-gqgx-xq4g |
Affected products (as reported)
Weakness: CWE-436 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N