CVE-2026-6321 fast-uri vulnerable to path traversal via percent-encoded dot segments
Attackers can bypass path-based security policies in applications using fast-uri by exploiting improper normalization of percent-encoded dot segments.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-6321?
CVE-2026-6321 is a high-severity path traversal vulnerability in fast-uri, published on 4 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-22
Which versions are affected by CVE-2026-6321?
4 open source packages ship an affected version, including fast-uri. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
fast-uri npm | All versions | 2.4.1 |
fast-uri npm | All versions | 2.4.1 |
fast-uri npm | From 3.0.0 | 3.1.1 |
fast-uri npm | From 3.0.0 | 3.1.1 |
Linux distribution packages (1)
python-pydata-sphinx-theme openSUSE:Tumbleweed | All versions | 0.17.1-1.1 |
Products include Openjsf Fast-Uri.
How do I fix CVE-2026-6321?
Upgrade fast-uri to a fixed version for your release line: 2.4.1 or 3.1.1.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-6321 being exploited?
There is no known exploitation of CVE-2026-6321 in the wild and no public exploit code.
Other vulnerabilities in fast-uri
- CVE-2026-84292 fast-uri vulnerable to authority injection via an unvalidated port in serialize
- CVE-2026-84394 fast-uri vulnerable to host confusion via an unclosed bracket in the URI authority
- CVE-2026-75899 fast-uri vulnerable to server-side request forgery via repeated hostname percent-decoding
- CVE-2026-75931 fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative references
- CVE-2026-75975 fast-uri vulnerable to server-side request forgery via malformed IPv6 normalization
Sources
Also known as CLEANSTART-2026-RD64552, CLEANSTART-2026-UQ15244, CLSA-2026-1784596352, CLSA-2026-1790854665, DEBIAN-CVE-2026-6321, ECHO-d17c-0010-d1d4 and 34 more.