CVE-2026-33807 (GCVE-0-2026-33807)
Vulnerability from cvelistv5 – Published: 2026-04-15 09:52 – Updated: 2026-04-15 13:09
VLAI?
Title
@fastify/express vulnerable to middleware path doubling causing authentication bypass in child plugin scopes
Summary
@fastify/express v4.0.4 and earlier contains a path handling bug in the onRegister function that causes middleware paths to be doubled when inherited by child plugins. When a child plugin is registered with a prefix that matches a middleware path, the middleware path is prefixed a second time, causing it to never match incoming requests. This results in complete bypass of Express middleware security controls, including authentication, authorization, and rate limiting, for all routes defined within affected child plugin scopes. No special configuration or request crafting is required.
Upgrade to @fastify/express v4.0.5 or later.
Severity ?
9.1 (Critical)
CWE
- CWE-436 - Interpretation Conflict
Assigner
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| fastify | @fastify/express |
Affected:
0 , < 4.0.5
(semver)
Unaffected: 4.0.5 (semver) |
Credits
FredKSchott
mcollina
UlisesGascon
climba03003
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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