CVE-2026-6270
criticalpriority · track · 0EPSS 0.005 · 42 %ileEUUSEPSS · scored 2026-10-27
@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
Technical severity, 0–10. One row per scoring source.
base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · high–critical · 8.3–9.1
ssvc
A stakeholder decision — act, attend, or track — from exploitation and impact.
weaknesses
The CWE weakness classes this flaw belongs to.
affected products (3)
Products and version ranges known to be affected.
advisories (1)
Vendor and ecosystem advisories describing this.
- GHSA-72c6-fx6q-fr5w@fastify/middie vulnerable to middleware authentication bypass in child plugin scopes2026-04-16ghsa · osvUS
### Impact `@fastify/middie` v9.3.1 and earlier incorrectly re-prefixes middleware paths when propagating them to child plugin scopes. When a child plugin is registered with a prefix that overlaps with a parent-scoped middleware path, the middleware path is modified during inheritance and silently fails to match incoming requests. This results in complete bypass of middleware security controls for all routes defined within affected child plugin scopes, including nested (grandchild) scopes. Authentication, authorization, rate limiting, and any other middleware-based security mechanisms are skipped. No special request crafting or configuration is required. This is the same vulnerability class as [GHSA-hrwm-hgmj-7p9c](https://github.com/fastify/fastify-express/security/advisories/GHSA-hrwm-hgmj-7p9c) (CVE-2026-33807) in `@fastify/express`. ### Patches Upgrade to `@fastify/middie` v9.3.2 or later. ### Workarounds None. Upgrade to the patched version.
also known as (3)
Other names and identifiers for this entity.
sources
Which sources assert this record, and when.
references (8)
External citations — patches, advisories, analysis.
- https://github.com/fastify/middie/releasesPatchcnnvd
- https://nvd.nist.gov/vuln/detail/CVE-2026-6270cnnvd
- https://cna.openjsf.org/security-advisories.htmlenisa_euvd
- https://github.com/fastify/fastify-express/security/advisories/GHSA-hrwm-hgmj-7p9cenisa_euvd
- https://github.com/fastify/middie/security/advisories/GHSA-72c6-fx6q-fr5wenisa_euvd
- https://cna.openjsf.org/security-advisories.htmlVendor Advisorynvd
- https://github.com/fastify/fastify-express/security/advisories/GHSA-hrwm-hgmj-7p9cExploitMitigationVendor Advisorynvd
- https://github.com/fastify/middie/security/advisories/GHSA-72c6-fx6q-fr5wVendor Advisorynvd
Attackers weaponise vulnerabilities like this against internet-exposed services. See what is exposed on your perimeter with a free passive scan.
Free scan