CVE-2026-76172: Fast uri Remote Code Execution Vulnerability
HIGHCVE-2026-76172 is a HIGH (CVSS 7.5) remote code execution vulnerability (CWE-177: Improper Handling of URL Encoding (Hex Encoding)) affecting Fast uri libraries in the npm ecosystem. The issue involves fast-uri vulnerable to host confusion via percent-encoded scheme normalization. Remediation is available by upgrading affected packages to version 2.4.5, 3.1.6, 4.1.3.
CVE-2026-76172 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-2026-76172
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@2.4.5npm install fast-uri@3.1.6npm install fast-uri@4.1.3Run 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-2026-76172, 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 2.4.5), 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-177: Improper Handling of URL Encoding (Hex Encoding), where the product does not properly handle when all or part of an input has been url encoded. 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-2026-76172 Affected Fast uri Versions
3 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
fast-uri
|
npm |
≥ 2.3.1
< 2.4.5
|
2.4.5
|
|
fast-uri
|
npm |
≥ 3.0.0
< 3.1.6
|
3.1.6
|
|
fast-uri
|
npm |
≥ 4.0.0
< 4.1.3
|
4.1.3
|
References
Frequently Asked Questions
What is CVE-2026-76172?
Which Fast uri versions are affected?
What version fixes CVE-2026-76172?
Is fast-uri affected?
What is the CVSS score of CVE-2026-76172?
What CWE is associated with CVE-2026-76172?
How can I check npm dependencies for CVE-2026-76172?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-jqff-g426-hqxp",
"modified" : "2026-09-02T15:41:53Z",
"published" : "2026-09-02T15:41:53Z",
"aliases" : [ "CVE-2026-76172" ],
"summary" : "fast-uri vulnerable to host confusion via percent-encoded scheme normalization",
"details" : "### Impact\n\n`fast-uri` decodes percent-encoded characters in the scheme component with the legacy global `unescape()` and serializes the result back as raw characters, without re-escaping it or validating it as a scheme. A scheme that decodes to characters outside the RFC 3986 scheme grammar can therefore introduce structure the original input did not contain.\n\nFor example, `%2f%2fevil.example:/pwn` parses with no authority (`parse().host` is `undefined`), but `resolve()` and `normalize()` return `//evil.example:/pwn`, which reparses with host `evil.example`. The `%uXXXX` form (`%u002f%u002fevil.example:/pwn`) produces the same result, and a scheme containing `%0d%0a` reaches the output as a raw CR LF.\n\nApplications that normalize or resolve untrusted URLs before a redirect check, host allowlist, or outbound request decision, especially ones that treat a missing authority as same-origin, can be steered to an attacker-chosen authority, and a normalized URI placed in a response header can carry an injected CR LF.\n\n### Patches\n\nUpgrade to `fast-uri` >= 4.1.3, or >= 3.1.6 in the v3.x release line, or >= 2.4.5 in the v2.x release line.\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" : "2.3.1"
}, {
"fixed" : "2.4.5"
} ]
} ]
}, {
"package" : {
"ecosystem" : "npm",
"name" : "fast-uri"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "3.0.0"
}, {
"fixed" : "3.1.6"
} ]
} ]
}, {
"package" : {
"ecosystem" : "npm",
"name" : "fast-uri"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "4.0.0"
}, {
"fixed" : "4.1.3"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/fastify/fast-uri/security/advisories/GHSA-jqff-g426-hqxp"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-76172"
}, {
"type" : "WEB",
"url" : "https://github.com/fastify/fast-uri/commit/37f3417c82994279656854f83ce938acd81c3862"
}, {
"type" : "WEB",
"url" : "https://github.com/fastify/fast-uri/commit/a941e626411f576f8d90883231e57b6c9d0ff98b"
}, {
"type" : "WEB",
"url" : "https://github.com/fastify/fast-uri/commit/c6a74bfd9d8c6b0df5362b3c7ae88d8021cb1e39"
}, {
"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/v2.4.5"
}, {
"type" : "WEB",
"url" : "https://github.com/fastify/fast-uri/releases/tag/v3.1.6"
}, {
"type" : "WEB",
"url" : "https://github.com/fastify/fast-uri/releases/tag/v4.1.3"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-177" ],
"severity" : "HIGH",
"github_reviewed" : true,
"github_reviewed_at" : "2026-09-02T15:41:53Z",
"nvd_published_at" : "2026-08-24T11:16:40Z"
}
}