CVE-2026-75899
fast-uri vulnerable to server-side request forgery via repeated hostname percent-decoding
Description
fast-uri is a URI parser for Node.js. It decodes percent escapes in a hostname during parsing and then decodes the parsed hostname a second time during authority recomposition, so a single call to normalize or resolve can turn nested percent-encoded input into a different network destination such as a loopback hostname or address. For example, a doubly encoded host that spells out a loopback name decodes to that live host in one operation, which contradicts RFC 3986 section 2.4 that an implementation must not decode the same string more than once. An application that normalizes or resolves an untrusted HTTP-family URI before outbound routing, redirect validation, or a host-policy check can receive a destination different from the one the original encoded host represented, giving a server-side request forgery and host-policy bypass primitive. This is an incomplete-fix variant of CVE-2026-6322. The affected versions are 2.4.1 up to but not including 2.4.5, 3.1.2 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 normalize percent escapes once and preserve encoded percent signs. 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-2026-75899.
| URL | Resource |
|---|---|
| https://cna.openjsf.org/security-advisories.html | Vendor Advisory |
| https://github.com/fastify/fast-uri/security/advisories/GHSA-fph4-wmhf-6fwf | Mitigation Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-75899 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-2026-75899
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-2026-75899 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-75899 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. Decodifica los escapes de porcentaje en un nombre de host durante el análisis y luego decodifica el nombre de host analizado una segunda vez durante la recomposición de la autoridad, por lo que una única llamada a normalizar o resolver puede convertir una entrada anidada codificada por porcentaje en un destino de red diferente, como un nombre de host o una dirección de bucle invertido. Por ejemplo, un host doblemente codificado que deletrea un nombre de bucle invertido se decodifica a ese host activo en una sola operación, lo que contradice la sección 2.4 de la RFC 3986 que establece que una implementación no debe decodificar la misma cadena más de una vez. Una aplicación que normaliza o resuelve un URI de la familia HTTP no confiable antes del enrutamiento saliente, la validación de redirección o una comprobación de política de host puede recibir un destino diferente al que representaba el host codificado original, lo que da lugar a una falsificación de petición del lado del servidor y una primitiva de omisión de política de host. Esta es una variante de corrección incompleta de CVE-2026-6322. Las versiones afectadas son 2.4.1 hasta, pero sin incluir, 2.4.5, 3.1.2 hasta, pero sin incluir, 3.1.6, y 4.0.0 hasta, pero sin incluir, 4.1.3. El problema está solucionado en 2.4.5, 3.1.6 y 4.1.3, que normalizan los escapes de porcentaje una vez y preservan los signos de porcentaje codificados. 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) 4.0.0 up to (excluding) 4.1.3 *cpe:2.3:a:openjsf:fast-uri:*:*:*:*:*:node.js:*:* versions from (including) 2.4.1 up to (excluding) 2.4.5 *cpe:2.3:a:openjsf:fast-uri:*:*:*:*:*:node.js:*:* versions from (including) 3.1.2 up to (excluding) 3.1.6 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-fph4-wmhf-6fwf 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-2026-75899', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-08-24T16:16:34.392088Z'} -
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': '2.4.1', 'lessThan': '2.4.5', 'versionType': 'semver'}, {'status': 'unaffected', 'version': '2.4.5', 'versionType': 'semver'}, {'status': 'affected', 'version': '3.1.2', 'lessThan': '3.1.6', 'versionType': 'semver'}, {'status': 'unaffected', 'version': '3.1.6', 'versionType': 'semver'}, {'status': 'affected', 'version': '4.0.0', '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 decodes percent escapes in a hostname during parsing and then decodes the parsed hostname a second time during authority recomposition, so a single call to normalize or resolve can turn nested percent-encoded input into a different network destination such as a loopback hostname or address. For example, a doubly encoded host that spells out a loopback name decodes to that live host in one operation, which contradicts RFC 3986 section 2.4 that an implementation must not decode the same string more than once. An application that normalizes or resolves an untrusted HTTP-family URI before outbound routing, redirect validation, or a host-policy check can receive a destination different from the one the original encoded host represented, giving a server-side request forgery and host-policy bypass primitive. This is an incomplete-fix variant of CVE-2026-6322. The affected versions are 2.4.1 up to but not including 2.4.5, 3.1.2 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 normalize percent escapes once and preserve encoded percent signs. 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-918 Added CWE CWE-174 Added Reference https://cna.openjsf.org/security-advisories.html Added Reference https://github.com/fastify/fast-uri/security/advisories/GHSA-fph4-wmhf-6fwf