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CVE-2026-14198

Fastify Fastify/middie vulnerability

9.1 CRITICALEPSS 0.52%
  1. Published1 Jul 2026

Description

@fastify/middie versions 9.1.0 through 9.3.2 decode the encoded slash %2F inside path parameter values before matching middleware paths, while Fastify's underlying router preserves the encoding during route lookup. The two layers disagree on the canonical request path, so the middleware fails to match a URL that the route handler does match. When middleware is used for authentication, authorization, rate limiting, or auditing on parameterized paths, an attacker can reach the protected handler by sending a single crafted URL with an encoded slash in the parameter position. The bypass is HTTP method agnostic and requires no authentication or special preconditions. Patches: upgrade to @fastify/middie 9.3.3. Workarounds: avoid parameterized middleware paths for security decisions, or enforce authentication at the route handler or via a Fastify hook that runs after the router has resolved the request.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected products

Fastify Fastify/middie≥ 9.1.0 < 9.3.3

Remediation

Fixed in
Fastify Fastify/middie≥ 9.3.3

References

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Frequently asked

Is CVE-2026-14198 being actively exploited?

CVE-2026-14198 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.52%.

How severe is CVE-2026-14198?

CVE-2026-14198 has a CVSS 3.1 base score of 9.1, rated critical. EPSS estimates a 0.52% probability of exploitation.

Which products are affected by CVE-2026-14198?

Affected products include Fastify Fastify/middie.

How do I fix CVE-2026-14198?

Upgrade affected software to a fixed version, for example Fastify Fastify/middie 9.3.3 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-14198 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.