CVE-2026-75931
fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative references
Description
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.
INFO
Published Date :
Aug. 24, 2026, 10:16 a.m.
Last Modified :
Oct. 14, 2026, 1:10 p.m.
Remotely Exploit :
No
Source :
ce714d77-add3-4f53-aff5-83d477b104bb
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | ce714d77-add3-4f53-aff5-83d477b104bb | ||||
| CVSS 3.1 | HIGH | MITRE-CVE |
Solution
- Upgrade to fast-uri version 2.4.5 or later.
- Upgrade to fast-uri version 3.1.6 or later.
- Upgrade to fast-uri version 4.1.3 or later.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-75931.
| URL | Resource |
|---|---|
| https://cna.openjsf.org/security-advisories.html | Vendor Advisory |
| https://github.com/fastify/fast-uri/security/advisories/GHSA-5jgf-p345-68v8 | Vendor Advisory Mitigation |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-75931 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-75931
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-75931 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-75931 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Translated by [email protected]
Oct. 14, 2026
Action Type Old Value New Value Added Translation Title: fast-uri, Description: fast-uri es un analizador de URI para Node.js. Canoniza un host a su forma ASCII solo cuyo la entrada lleva un esquema explícito, por lo que una referencia relativa al esquema, como un host precedido por dos barras, se devuelve con su host literalmente y sin error establecido. Como resultado, los propios puntos de entrada de fast-uri discrepan entre sí: parse, resolve, normalize y equal pueden producir hosts diferentes para la misma entrada dependiendo únicamente de si un esquema está escrito, y equal puede devolver veredictos opuestos para el mismo par de hosts. Una aplicación que extrae un host con fast-uri para verificarlo contra una lista de políticas y luego resuelve la misma referencia puede tomar su decisión sobre un host mientras el destino es otro, lo que permite la confusión de hosts y la elusión de políticas. Las versiones afectadas son 2.4.2 hasta, pero sin incluir, 2.4.5; 3.1.3 hasta, pero sin incluir, 3.1.6; y 4.0.1 hasta, pero sin incluir, 4.1.3. El problema está solucionado en 2.4.5, 3.1.6 y 4.1.3, que canonizan el host de manera consistente a lo largo de la ruta de resolución. Los usuarios deben actualizar a una versión parcheada. -
Initial Analysis by [email protected]
Sep. 02, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:openjsf:fast-uri:*:*:*:*:*:node.js:*:* versions from (including) 2.4.2 up to (excluding) 2.4.5 *cpe:2.3:a:openjsf:fast-uri:*:*:*:*:*:node.js:*:* versions from (including) 3.1.3 up to (excluding) 3.1.6 *cpe:2.3:a:openjsf:fast-uri:*:*:*:*:*:node.js:*:* versions from (including) 4.0.1 up to (excluding) 4.1.3 Added Reference Type openjs: https://cna.openjsf.org/security-advisories.html Types: Vendor Advisory Added Reference Type openjs: https://github.com/fastify/fast-uri/security/advisories/GHSA-5jgf-p345-68v8 Types: Mitigation, Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Aug. 24, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-75931', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-08-24T16:28:35.705177Z'} -
New CVE Received by ce714d77-add3-4f53-aff5-83d477b104bb
Aug. 24, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'fast-uri', 'product': 'fast-uri', 'versions': [{'status': 'affected', 'version': '2.4.2', 'lessThan': '2.4.5', 'versionType': 'semver'}, {'status': 'unaffected', 'version': '2.4.5', 'versionType': 'semver'}, {'status': 'affected', 'version': '3.1.3', 'lessThan': '3.1.6', 'versionType': 'semver'}, {'status': 'unaffected', 'version': '3.1.6', 'versionType': 'semver'}, {'status': 'affected', 'version': '4.0.1', 'lessThan': '4.1.3', 'versionType': 'semver'}, {'status': 'unaffected', 'version': '4.1.3', 'versionType': 'semver'}], 'packageURL': 'pkg:npm/fast-uri', 'defaultStatus': 'unaffected'}] Added Description 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. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Added CWE CWE-436 Added Reference https://cna.openjsf.org/security-advisories.html Added Reference https://github.com/fastify/fast-uri/security/advisories/GHSA-5jgf-p345-68v8