CVE-2026-112362 (GCVE-0-2026-112362)
Vulnerability from cvelistv5 – Published: 2026-10-27 11:27 – Updated: 2026-11-04 17:11
VLAI
EPSS
VEX
Title
@fastify/express vulnerable to path-scoped middleware bypass via absolute-form request targets
Summary
@fastify/express is a Fastify plugin that runs Express middleware inside Fastify. In versions 4.0.5 through 4.0.8, when Fastify runs with the non-default ignoreDuplicateSlashes option enabled, the plugin matches path-scoped Express middleware against a URL whose duplicate-slash normalization has also collapsed the separator after an absolute-form request target's scheme, so Fastify's router resolves the request to the scoped path and runs the handler while the Express layer no longer sees that path. As a result, a request using an absolute-form target can reach a handler on a scoped route such as an admin path while the middleware for authentication, authorization, or rate limiting is skipped. An unauthenticated attacker needs only the non-default ignoreDuplicateSlashes option to be enabled. The issue is fixed in @fastify/express 4.0.9, and users should upgrade to 4.0.9 or later. As a workaround, enforce authentication in a Fastify hook such as preHandler that runs after the router resolves the request, or leave ignoreDuplicateSlashes at its default.
Severity
9.1 (Critical)
SSVC
Exploitation: none
Automatable: yes
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-11-04 17:11 UTC
CWE
- CWE-436 - Interpretation Conflict
Assigner
References
Impacted products
1 product
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| @fastify/express | @fastify/express |
Affected:
4.0.5 , < 4.0.9
(semver)
Unaffected: 4.0.9 (semver) |
guessed |
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Browse all ATT&CK techniques and the vulnerabilities related to each.
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