Critical severity · published Apr 16, 2026
CVE-2026-6270
@fastify/middie vulnerable to middleware authentication bypass in child plugin scopes
9.1
CVSS
0.5%
EPSS
No
On KEV
Description
@fastify/middie versions 9.3.1 and earlier do not register inherited middleware directly on child plugin engine instances. When a Fastify application registers authentication middleware in a parent scope and then registers child plugins with @fastify/middie, the child scope does not inherit the parent middleware. This allows unauthenticated requests to reach routes defined in child plugin scopes, bypassing authentication and authorization checks. Upgrade to @fastify/middie 9.3.2 to fix this issue. There are no workarounds.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.5% · higher than 42% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
FA
@fastify/middie · @fastify/middie
before 9.3.2 · source: vendor
FA
Fastify/middie · Fastify
before 9.3.2 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-6270
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-6270
Vendor Advisory
https://cna.openjsf.org/security-advisories.html
Exploit
https://github.com/fastify/fastify-express/security/advisories/GHSA-hrwm-hgmj-7p9c
Vendor Advisory
https://github.com/fastify/middie/security/advisories/GHSA-72c6-fx6q-fr5w
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