Description
fast-uri is a dependency-free RFC 3986 URI parser and serializer for Node.js. In versions before 2.4.8, from 3.0.0 through 3.1.8, and from 4.0.0 through 4.2.2, fast-uri percent-decodes the scheme component with the legacy global unescape() function before validating it, so an input whose decoded scheme is a dangerous token is emitted as a live scheme even though RFC 3986 does not allow percent-encoding in a scheme and no other parser accepts it. An application that screens dangerous schemes on the raw input and then stores or renders the normalized or resolved result can turn an inert string into an executable javascript, data, or vbscript URL, producing a stored or reflected cross-site scripting vector, and the equal() comparison treats an encoded and a plain scheme as the same, which can bypass equality-based allowlists. The issue is fixed in fast-uri 2.4.8, 3.1.9, and 4.2.3, and users should upgrade to one of these versions or later. As a workaround, reject input whose scheme part contains a percent sign, or check the parsed scheme against an allowlist after normalization and use that same parsed result rather than the raw string.
Published: 2026-10-20
Score: 6.1 Medium
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
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Remediation

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History

Tue, 20 Oct 2026 12:45:00 +0000

Type Values Removed Values Added
Description fast-uri is a dependency-free RFC 3986 URI parser and serializer for Node.js. In versions before 2.4.8, from 3.0.0 through 3.1.8, and from 4.0.0 through 4.2.2, fast-uri percent-decodes the scheme component with the legacy global unescape() function before validating it, so an input whose decoded scheme is a dangerous token is emitted as a live scheme even though RFC 3986 does not allow percent-encoding in a scheme and no other parser accepts it. An application that screens dangerous schemes on the raw input and then stores or renders the normalized or resolved result can turn an inert string into an executable javascript, data, or vbscript URL, producing a stored or reflected cross-site scripting vector, and the equal() comparison treats an encoded and a plain scheme as the same, which can bypass equality-based allowlists. The issue is fixed in fast-uri 2.4.8, 3.1.9, and 4.2.3, and users should upgrade to one of these versions or later. As a workaround, reject input whose scheme part contains a percent sign, or check the parsed scheme against an allowlist after normalization and use that same parsed result rather than the raw string.
Title fast-uri vulnerable to URI scheme spoofing via percent-encoded scheme decoding
Weaknesses CWE-1286
CWE-172
CWE-180
References
Metrics threat_severity

None

 cvssV3_1

{'score': 6.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N'}

threat_severity

Moderate

Subscriptions

No data.

cve-icon MITRE

Status: PUBLISHED

Assigner: openjs

Published:

Updated: 2026-10-20T07:03:47.312Z

Reserved: 2026-10-13T19:49:41.192Z

Link: CVE-2026-110306

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-10-20T07:17:08.810

Modified: 2026-10-20T07:17:08.810

Link: CVE-2026-110306

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-10-20T07:03:47Z

Links: CVE-2026-110306 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-10-20T16:00:16Z

Weaknesses
  • CWE-1286

    Improper Validation of Syntactic Correctness of Input

  • CWE-172

    Encoding Error

  • CWE-180

    Incorrect Behavior Order: Validate Before Canonicalize