Interpretation Conflict Affecting @fastify/express package, versions >=4.0.5 <4.0.9
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-FASTIFYEXPRESS-21755407
- published27 Oct 2026
- disclosed27 Oct 2026
- creditAjith Prabhu
Introduced: 27 Oct 2026
NewCVE-2026-112362 (opens in a new tab)How to fix?
Upgrade @fastify/express to version 4.0.9 or higher.
Overview
@fastify/express is an Express compatibility layer for Fastify
Affected versions of this package are vulnerable to Interpretation Conflict via the normalizeUrl function in index.js when the non-default ignoreDuplicateSlashes option is enabled. When an absolute-form request target (e.g. http://host/path) is processed, duplicate-slash normalization collapses the separator after the scheme, causing Fastify's router to resolve the request to a scoped path and execute the handler while the Express middleware layer no longer sees that path. An unauthenticated attacker can exploit this discrepancy to bypass path-scoped Express middleware, including authentication and authorization layers, achieving unauthorized access to protected resources.
Note: This is only exploitable when the non-default ignoreDuplicateSlashes option is explicitly enabled.