Description
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.
Published: 2026-08-24
Score: 7.5 High
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
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Remediation

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History

Mon, 24 Aug 2026 11:45:00 +0000

Type Values Removed Values Added
First Time appeared Fast-uri
Fast-uri fast-uri
Vendors & Products Fast-uri
Fast-uri fast-uri

Mon, 24 Aug 2026 10:15:00 +0000

Type Values Removed Values Added
Description 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.
Title fast-uri vulnerable to server-side request forgery via malformed IPv6 normalization
Weaknesses CWE-20
CWE-918
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N'}


Subscriptions

Fast-uri Fast-uri
cve-icon MITRE

Status: PUBLISHED

Assigner: openjs

Published:

Updated: 2026-08-24T09:58:07.698Z

Reserved: 2026-08-18T18:09:48.366Z

Link: CVE-2026-75975

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-08-24T10:16:40.237

Modified: 2026-08-24T10:16:40.237

Link: CVE-2026-75975

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-24T11:30:03Z

Weaknesses