AIKIDO-2026-945818
fast-uri is vulnerable to Server-Side Request Forgery (SSRF)
75
High Risk
This Affects:
fast-uriTL;DR
The library percent-decodes the hostname twice, once during parsing and again during authority recomposition. Nested percent-encoded hostnames therefore collapse to a different host such as localhost only after normalization runs. Applications that enforce allowlists or SSRF protections against the pre-normalization URI can be redirected to internal addresses or cloud metadata endpoints. The fix removes the redundant second decode of the host component in normalize() and resolve().
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range and your application normalizes or resolves untrusted or externally influenced URIs before performing allowlist or SSRF checks.
Background info
fast-uri is vulnerable to Server-Side Request Forgery (SSRF) in versions 2.4.1 - 2.4.4, 3.1.2 - 3.1.5 and 4.0.0 - 4.1.2.
How to fix this
Upgrade the fast-uri library to the patch version.
Links
GitHub Release
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SOC 2Compliant
ISO 27001Compliant