CVE-2026-18446: Fast uri Fast-uri Vulnerable To Host Confusion Vulnerability
HIGHCVE-2026-18446 is a HIGH (CVSS 7.5) fast-uri vulnerable to host confusion vulnerability (CWE-436: Interpretation Conflict) affecting Fast uri libraries in the npm ecosystem. The issue involves fast-uri vulnerable to host confusion via backslash authority introducer. Remediation is available by upgrading affected packages to version 2.4.4, 3.1.5, 4.1.2.
CVE-2026-18446 at a Glance
Security Impact
CVSS: 7.5
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N).
How to Fix CVE-2026-18446
To remediate this vulnerability, upgrade all affected Fast uri dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
npm install fast-uri@2.4.4npm install fast-uri@3.1.5npm install fast-uri@4.1.2Run the following command in your project directory to verify that all resolved dependencies use the patched release:
npm ls fast-uriHow to Check if You Are Affected
To determine whether your Node.js application is affected by CVE-2026-18446, inspect your project dependencies using npm:
npm ls fast-uriAnalyze the terminal output to locate any version of Fast uri in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.4.4), your application is affected.
Note: The npm ls fast-uri command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-436: Interpretation Conflict, where 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. In Fast uri, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2026-18446 Affected Fast uri Versions
3 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
fast-uri
|
npm |
< 2.4.4
|
2.4.4
|
|
fast-uri
|
npm |
≥ 3.0.0
< 3.1.5
|
3.1.5
|
|
fast-uri
|
npm |
≥ 4.0.0
< 4.1.2
|
4.1.2
|
References
Frequently Asked Questions
What is CVE-2026-18446?
Which Fast uri versions are affected?
What version fixes CVE-2026-18446?
Is fast-uri affected?
What is the CVSS score of CVE-2026-18446?
What CWE is associated with CVE-2026-18446?
How can I check npm dependencies for CVE-2026-18446?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-7p8r-x3mc-p8w7",
"modified" : "2026-08-03T19:16:43Z",
"published" : "2026-08-03T19:16:43Z",
"aliases" : [ "CVE-2026-18446" ],
"summary" : "fast-uri vulnerable to host confusion via backslash authority introducer",
"details" : "### Impact\n\n`fast-uri` v4.1.1 and earlier require a literal `//` to recognize a URI authority, so a reference that uses `\\\\`, `/\\`, or `\\/` as the authority introducer (in place of `//`, after an optional scheme) is parsed with no authority: the sequence and everything after it fold into the path. Node's native WHATWG `URL` (used by `fetch()`, `undici`, and Node's `http`/`https` clients) instead treats `\\` as interchangeable with `/` for special schemes (`http`, `https`, `ws`, `wss`, `ftp`, `file`), so the two parsers extract different hosts from the same input.\n\nFor example, `fast-uri` resolves `\\\\evil.com/path` against base `https://allowed.com/` to `https://allowed.com/%5C%5Cevil.com/path` (confined to the trusted host), while Node's WHATWG URL resolves the same reference to `https://evil.com/path`.\n\nApplications that use `fast-uri` to enforce host-based policy (allowlists, denylists, loopback/SSRF filtering, redirect validation, outbound proxy routing) before passing the same URL into Node's URL or `fetch()` consumers see a policy/use desync and can be steered to an unintended destination.\n\n### Patches\n\nUpgrade to `fast-uri` v4.1.2, v3.1.5, v2.4.4.\n\n### Workarounds\n\nNone. Upgrade to the patched version.",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "npm",
"name" : "fast-uri"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "2.4.4"
} ]
} ]
}, {
"package" : {
"ecosystem" : "npm",
"name" : "fast-uri"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "3.0.0"
}, {
"fixed" : "3.1.5"
} ]
} ]
}, {
"package" : {
"ecosystem" : "npm",
"name" : "fast-uri"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "4.0.0"
}, {
"fixed" : "4.1.2"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/fastify/fast-uri/security/advisories/GHSA-7p8r-x3mc-p8w7"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-18446"
}, {
"type" : "WEB",
"url" : "https://github.com/fastify/fast-uri/commit/f3c6c905f47831007490f466c5945012e905cc52"
}, {
"type" : "WEB",
"url" : "https://cna.openjsf.org/security-advisories.html"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/fastify/fast-uri"
}, {
"type" : "WEB",
"url" : "https://github.com/fastify/fast-uri/releases/tag/v4.1.2"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-436" ],
"severity" : "HIGH",
"github_reviewed" : true,
"github_reviewed_at" : "2026-08-03T19:16:43Z",
"nvd_published_at" : "2026-07-31T15:16:27Z"
}
}