fastify fast-uri up to 2.4.4/3.1.5/4.1.2 URI Parser parse/resolve/normalize/equal interpretation conflict

Summaryinfo

A vulnerability was found in fastify fast-uri up to 2.4.4/3.1.5/4.1.2. It has been classified as problematic. The affected element is the function parse/resolve/normalize/equal of the component URI Parser. This manipulation causes input validation. The identification of this vulnerability is CVE-2026-75931. It is possible to initiate the attack remotely. There is no exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability has been found in fastify fast-uri up to 2.4.4/3.1.5/4.1.2 and classified as problematic. Affected by this vulnerability is the function parse/resolve/normalize/equal of the component URI Parser. The manipulation with an unknown input leads to a input validation vulnerability. The CWE definition for the vulnerability is CWE-436. 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. As an impact it is known to affect integrity. The summary by CVE is:

fast-uri is a URI parser for Node.js. It canonicalizes a host to its ASCII form only when the input carries an explicit scheme, so a scheme-relative reference such as a host preceded by two slashes is returned with its host verbatim and no error set. As a result fast-uri's own entry points disagree with each other: parse, resolve, normalize, and equal can yield different hosts for the same input depending only on whether a scheme is written out, and equal can return opposite verdicts for the same pair of hosts. An application that extracts a host with fast-uri to check it against a policy list and then resolves the same reference can make its decision on one host while the destination is another, enabling host confusion and policy bypass. The affected versions are 2.4.2 up to but not including 2.4.5, 3.1.3 up to but not including 3.1.6, and 4.0.1 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which canonicalize the host consistently across the resolve path. Users should upgrade to a patched version.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-75931 since 08/18/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details are known, but no exploit is available.

Upgrading to version 2.4.5, 3.1.6 or 4.1.3 eliminates this vulnerability.

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Productinfo

Vendor

• fastify

Name

• fast-uri

Version

• 2.4.0
• 2.4.1
• 2.4.2
• 2.4.3
• 2.4.4
• 3.1.0
• 3.1.1
• 3.1.2
• 3.1.3
• 3.1.4
• 3.1.5
• 4.1.0
• 4.1.1
• 4.1.2

Website

• Product: https://github.com/fastify/fast-uri/

CPE 2.3info

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CPE 2.2info

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