fast-uri vulnerable to server-side request forgery via repeated hostname percent-decoding (CVE-2026-75899)

What is affected, what to do

A flaw was found in fast-uri, a URI parser for Node.js. The component incorrectly decodes percent escapes in a hostname twice during URI parsing and authority recomposition.

Update Fast-uri to version 2.4.5, Fast-uri to version 3.1.6, Fast-uri to version 4.1.3.

Affected

• Fast-uri lt 2.4.1..2.4.5
• Fast-uri lt 3.1.2..3.1.6
• Fast-uri lt 4.0.0..4.1.3

Fixed in

• Fast-uri 2.4.5
• Fast-uri 3.1.6
• Fast-uri 4.1.3

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Metrics

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2

NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

Read in glossary

High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.

CRA

The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

Read in glossary

From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.

ISO/IEC 27001

ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

Read in glossary

Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

A flaw was found in fast-uri, a URI parser for Node.js. The component incorrectly decodes percent escapes in a hostname twice during URI parsing and authority recomposition. This double decoding can allow a remote attacker to manipulate a URI to point to a different network destination, such as a loopback address. This vulnerability can lead to Server-Side Request Forgery (SSRF) and bypass host-based security policies.

Source: redhat_csaf, BSI WID Portal, BSI CSAF, OSV (Open Source Vulnerabilities), cvelistv5, NVD (NIST), GitHub Security Advisories

Vendors and products

• Fast-uri Fast-uri
• Openjsf OpenJS Foundation fast-uri

Weakness classes (CWE)

• CWE-174Double Decoding of the Same Data

  Variant

  The product decodes the same input twice, which can limit the effectiveness of any protection mechanism that occurs in between the decoding operations.

  Entry at MITRE CWE-174

• CWE-918Server-Side Request Forgery (SSRF)

  Base

  The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.

  Entry at MITRE CWE-918

References & sources

• github.comfastify/fast-uri/security/advisories/GHSA-fph4-wmhf-6fwf
• cna.openjsf.orgsecurity-advisories.html
• NVD (NIST)vuln/detail/CVE-2026-75899advisory
• github.comfastify/fast-uri/commit/2642290672e7211c990aaed3749c2ce667d0af4fweb
• github.comfastify/fast-uri/commit/8c15dbe94ec50bb8e595791ebb42c35cef0fd304web
• github.comfastify/fast-uri/commit/ae92a4c5d8c4b6c9e447f048d5fcbde7eebd5514web
• github.comfastify/fast-uripackage
• github.comfastify/fast-uri/releases/tag/v2.4.5web
• github.comfastify/fast-uri/releases/tag/v3.1.6web
• github.comfastify/fast-uri/releases/tag/v4.1.3web

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

1. 02.09.2026Initial analysis by NVDNVD

   Newly listed as affected:

   • Openjsf OpenJS Foundation fast-uri (4.0.0 – before 4.1.3; 2.4.1 – before 2.4.5; 3.1.2 – before 3.1.6)

   New references:

   • https://cna.openjsf.org/security-advisories.html
   • https://github.com/fastify/fast-uri/security/advisories/GHSA-fph4-wmhf-6fwf
   Show 3 original changes

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   Product configuration	added	—	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
   Reference type	added	—	openjs: https://cna.openjsf.org/security-advisories.html Types: Vendor Advisory
   Reference type	added	—	openjs: https://github.com/fastify/fast-uri/security/advisories/GHSA-fph4-wmhf-6fwf Types: Mitigation, Vendor Advisory

   Source identifier: nvd@nist.gov

2. 24.08.2026Record modifiedCISA ADP

   CISA assessment (SSVC): exploitation: none known, automatable: yes

   Show the original change

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   SSVC assessment	added	—	{"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"}

   Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

3. 24.08.2026ReceivedOpenJS Foundation

   CVSS V3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

   Weakness type: CWE-918, CWE-174

   Description added or changed

   New references:

   • https://cna.openjsf.org/security-advisories.html
   • https://github.com/fastify/fast-uri/security/advisories/GHSA-fph4-wmhf-6fwf
   Show 7 original changes

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   Affected versions (publisher)	added	—	fast-uri
   Description	added	—	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.
   CVSS	added	—	AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
   Weakness type (CWE)	added	—	CWE-918
   Weakness type (CWE)	added	—	CWE-174
   Reference	added	—	https://cna.openjsf.org/security-advisories.html
   Reference	added	—	https://github.com/fastify/fast-uri/security/advisories/GHSA-fph4-wmhf-6fwf

   Source identifier: ce714d77-add3-4f53-aff5-83d477b104bb

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