CVE-2026-6321

Modified Modified - Updated After Analysis

Path Normalization Bypass in fast-uri Library

Publication date: 2026-05-04

Last updated on: 2026-07-02

Assigner: openjs

Description

fast-uri decoded percent-encoded path separators and dot segments before applying dot-segment removal in its normalize() and equal() functions. Encoded path data was treated like real slashes and parent-directory references, so distinct URIs could collapse onto the same normalized path. Applications that normalize or compare attacker-controlled URLs to enforce path-based policy can be bypassed, with a path that appears confined under an allowed prefix normalizing to a different location. Versions <= 3.1.0 are affected. Update to 3.1.1 or later.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published

2026-05-04

Last Modified

2026-07-02

Generated

2026-07-06

AI Q&A

2026-05-05

EPSS Evaluated

2026-07-05

NVD

CVE-2026-6321

EUVD

EUVD-2026-27129

Affected Vendors & Products

Vendor	Product	Version / Range
fast-uri	fast-uri	to 3.1.0 (inc)
fast-uri	fast-uri	3.1.1

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-22	The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

Attack-Flow Graph

Executive Summary

This vulnerability exists in the fast-uri library versions up to 3.1.0. The issue is that the library decodes percent-encoded path separators and dot segments before applying dot-segment removal in its normalize() and equal() functions. Because encoded path data is treated like actual slashes and parent-directory references, different URIs that should be distinct can end up collapsing into the same normalized path.

As a result, applications that rely on normalizing or comparing attacker-controlled URLs to enforce path-based policies can be bypassed. An attacker can craft a path that appears to be confined under an allowed prefix but actually normalizes to a different location, potentially circumventing security controls.

Impact Analysis

The vulnerability can allow attackers to bypass path-based security policies by exploiting the way URLs are normalized. This means that an attacker could access resources or perform actions that should be restricted by the application’s URL path controls.

Since the CVSS score indicates a high impact on integrity (I:H) with no impact on confidentiality or availability, the main risk is unauthorized modification or manipulation of data or application behavior through crafted URLs.

Mitigation Strategies

To mitigate this vulnerability, update fast-uri to version 3.1.1 or later, as versions up to 3.1.0 are affected.

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