CVE-2026-6321: fast-uri vulnerable to path traversal via percent-encoded dot segments

Vulnerability summary

CVE-2026-6321 is a high (CVSS 7.5) vulnerability in fast-uri. EPSS estimates a 0.63% chance of exploitation in the next 30 days, higher than 50.4% of scored vulnerabilities.

Timeline

1. 04-05-2026
   PublishedVulnerability first disclosed.
2. 10-09-2026
   Last modifiedVulnerability information updated.

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.

• CWE-22Improper Limitation of a Pathname to a Restricted DirectoryThe 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.