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GHSA-8p85-9qpw-fwgw
No affected components available
Summary
A path normalization inconsistency in @fastify/middie can result in authentication/authorization bypass when using path-scoped middleware (for example, app.use('/secret', auth)).
When Fastify router normalization options are enabled (such as ignoreDuplicateSlashes, useSemicolonDelimiter, and related trailing-slash behavior), crafted request paths may bypass middleware checks while still being routed to protected handlers.
Impact
An unauthenticated remote attacker can access endpoints intended to be protected by middleware-based auth/authorization controls by sending specially crafted URL paths (for example, //secret or /secret;foo=bar), depending on router option configuration.
This may lead to unauthorized access to protected functionality and data exposure.
Affected versions
- Confirmed affected:
@fastify/middie@9.1.0 - All versions prior to the patch are affected.
Patched versions
- Fixed in: 9.2.0
Details
The issue is caused by canonicalization drift between:
@fastify/middiepath matching forapp.use('/prefix', ...), and- Fastify/find-my-way route lookup normalization.
Because middleware and router did not always evaluate the same normalized path, auth middleware could be skipped while route resolution still succeeded.
Workarounds
Until patched version is deployed:
- Avoid relying solely on path-scoped middie guards for auth/authorization.
- Enforce auth at route-level handlers/hooks after router normalization.
- Disable risky normalization combinations only if operationally feasible.
Resources
- Fluid Attacks Disclosure Policy: https://fluidattacks.com/advisories/policy
- Fluid Attacks advisory URL: https://fluidattacks.com/advisories/jimenez
Credits
- Cristian Vargas (Fluid Attacks Research Team) — discovery and report.
- Oscar Uribe (Fluid Attacks) — coordination and disclosure.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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