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

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-04 · updated 2026-09-10
Weakness: CWE-22

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.

Affected products

fast-uri: before 3.1.1 — fixed in 3.1.1

How to fix

Upgrade to a fixed version: fast-uri 3.1.1. Check the vendor advisory for mitigations.

References

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