CVE-2026-6322: fast-uri vulnerable to host confusion via percent-encoded authority delimiters

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-05 · updated 2026-09-10
Weakness: CWE-436

Description

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.

Affected products

fast-uri: before 3.1.2 — fixed in 3.1.2

How to fix

Upgrade to a fixed version: fast-uri 3.1.2. Check the vendor advisory for mitigations.

References

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