Impact

fast-uri v3.1.0 and earlier decodes percent-encoded path separators (%2F) and dot segments (%2E) before applying dot-segment removal in normalize() and equal(). This makes encoded path data behave like real / and .., so distinct URIs collapse onto the same normalized path.

For example, http://example.com/public/%2e%2e/admin normalizes to http://example.com/admin, and equal() considers them the same URI.

Applications that normalize or compare attacker-controlled URLs to enforce path-based policy can be bypassed. A path that looks confined under an allowed prefix can normalize to a different location.

Patches

Upgrade to fast-uri >= 3.1.1.

Workarounds

None. Upgrade to the patched version.