How severe is CVE-2026-6270?

CVE-2026-6270 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2026-6270 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (39th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-6270?

CVE-2026-6270 affects Fastify Fastify/middie. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-6270?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2026-6270 have an EU (EUVD) identifier?

Yes. CVE-2026-6270 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-23241.

When was CVE-2026-6270 published?

CVE-2026-6270 was published on 2026-04-16 and last updated on 2026-06-17.

CVE-2026-6270

CVE-2026-6270 is a critical-severity vulnerability in Fastify Fastify/middie with a CVSS 3.x base score of 9.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-436.

Key facts

Severity: Critical (CVSS 3.x base score 9.1)
EPSS exploit prediction: 0% (39th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-23241
Weakness: CWE-436
Affected product: Fastify Fastify/middie
Published: 2026-04-16
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2026-6270?: @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.
How severe is CVE-2026-6270?: CVE-2026-6270 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-6270 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (39th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-6270?: CVE-2026-6270 affects Fastify Fastify/middie. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-6270?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2026-6270 have an EU (EUVD) identifier?: Yes. CVE-2026-6270 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-23241.
When was CVE-2026-6270 published?: CVE-2026-6270 was published on 2026-04-16 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:fastify:fastify\/middie:*:*:*:*:*:node.js:*:*

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