fastify fast-uri up to 2.4.4/3.1.5/4.1.2 IPv6 Literal Parser input validation

Summaryinfo

A vulnerability labeled as problematic has been found in fastify fast-uri up to 2.4.4/3.1.5/4.1.2. Affected by this vulnerability is an unknown functionality of the component IPv6 Literal Parser. The manipulation results in input validation. This vulnerability is cataloged as CVE-2026-75975. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability classified as problematic has been found in fastify fast-uri up to 2.4.4/3.1.5/4.1.2. Affected is an unknown part of the component IPv6 Literal Parser. The manipulation with an unknown input leads to a input validation vulnerability. CWE is classifying the issue as CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. This is going to have an impact on integrity. CVE summarizes:

fast-uri is a URI parser for Node.js. Its custom parser for bracketed IPv6 literals does not validate the complete IPv6 grammar, so invalid trailing text in an authority can be silently discarded and a malformed attacker-controlled host is turned into a different valid IPv6 destination. For example, a bracketed literal with invalid trailing characters is normalized to the unspecified address, which a Node HTTP client then connects to a local service over loopback, and other malformed literals collapse to private-range addresses. No error is set on the parsed result, so an application checking the error field cannot detect the rewrite. An application that normalizes untrusted URLs before outbound requests, redirects, proxy routing, or address-policy enforcement can be redirected to a local or private IPv6 target, giving a server-side request forgery and address-policy bypass primitive. The affected versions are 2.3.1 up to but not including 2.4.5, 3.0.0 up to but not including 3.1.6, and 4.0.0 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which validate bracketed IP literals against the full grammar and mark malformed literals as authority errors. Users should upgrade to a patched version.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-75975 since 08/18/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. The technical details are unknown and an exploit is not 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/

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CPE 2.2info

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