CVE-2026-6322: fast-uri vulnerable to host confusion via percent-encoded authority delimiters
Impact
fast-uri v3.1.1 and earlier decodes percent-encoded authority delimiters (%40 as @, %3A as :) inside the host component and serializes them back as raw characters. This changes the URI structure, turning a hostname into userinfo plus a different host.
For example, http://trusted.com%40evil.com/ normalizes to http://trusted.com@evil.com/, which reparses as host evil.com with userinfo trusted.com.
Applications that normalize untrusted URLs before host allowlist checks, redirect validation, or outbound request routing can be steered to a different authority than the original URL appeared to contain.
Patches
Upgrade to fast-uri >= 3.1.2.
Workarounds
None. Upgrade to the patched version.
Other sources
fast-uri normalize() decoded percent-encoded authority delimiters inside the host component and then re-emitted them as raw delimiters during serialization. A host that combined an allowed domain, an encoded at-sign, and a different domain was re-emitted with the at-sign as a raw userinfo separator, changing the URI's authority to the second domain. Applications that normalize untrusted URLs before host allowlist checks, redirect validation, or outbound request routing can be steered to a different authority than the input appeared to specify. Versions <= 3.1.1 are affected. Update to 3.1.2 or later.
— MITRE
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-6322?
CVE-2026-6322 is considered a medium severity vulnerability due to potential exploitation leading to host confusion.
How do I fix CVE-2026-6322?
To mitigate CVE-2026-6322, update the fast-uri package to version 3.1.2 or later.
What software is affected by CVE-2026-6322?
CVE-2026-6322 affects the fast-uri package versions up to and including 3.1.1.
What types of vulnerabilities does CVE-2026-6322 represent?
CVE-2026-6322 represents a host confusion vulnerability due to improper handling of percent-encoded authority delimiters.
Is there an exploit available for CVE-2026-6322?
As of now, there are no public exploits reported for CVE-2026-6322, but the vulnerability itself poses risks that should be addressed.