Interpretation Conflict Affecting @fastify/middie package, versions <9.3.2
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JS-FASTIFYMIDDIE-16098212
- published17 Apr 2026
- disclosed16 Apr 2026
- creditFred K. Schott
Introduced: 16 Apr 2026
NewCVE-2026-33804 (opens in a new tab)How to fix?
Upgrade @fastify/middie to version 9.3.2 or higher.
Overview
@fastify/middie is a Middleware engine for Fastify
Affected versions of this package are vulnerable to Interpretation Conflict in the resolveNormalizationOptions() function's deprecated ignoreDuplicateSlashes configuration option. An attacker can bypass middleware by crafting URLs with duplicate leading slashes, resulting in unauthorized access to protected routes.
Workaround
This vulnerability can be mitigated by migrating from the deprecated top-level ignoreDuplicateSlashes: true to routerOptions: { ignoreDuplicateSlashes: true }.