Fast-URI Path Normalization Bypass Fast-URI <=3.1.0
CVE-2026-6321 Published on May 4, 2026
fast-uri vulnerable to path traversal via percent-encoded dot segments
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.
Weakness Type
What is a Directory traversal Vulnerability?
The software 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 software 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.
CVE-2026-6321 has been classified to as a Directory traversal vulnerability or weakness.
Affected Versions
fast-uri:- Before 3.1.1 is affected.
- Version 3.1.1 is unaffected.