EUVD-2026-40947Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Remote unauthenticated single malformed request triggers the crash (AV:N/AC:L/PR:N/UI:N); impact is availability-only process termination with no data exposure (C:N/I:N/A:H).
Primary rating from Vendor (openjs).
CVSS VectorVendor: openjs
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Lifecycle Timeline
2DescriptionCVE.org
@fastify/middie versions 9.1.0 through 9.3.2 fail to guard the URL normalization step used by the standalone engine when incoming request paths contain malformed percent-encoded sequences. Inputs such as an incomplete percent escape or a truncated multibyte sequence cause the underlying decoder to throw synchronously, and the exception escapes the middie normalize step and terminates the Node.js process. The bypass affects applications that call middie.run directly on the standalone engine API, causing an immediate denial of service for all connected clients until restart. Applications using the Fastify plugin path are not affected because Fastifys error handler catches the exception. Patches: upgrade to @fastify/middie 9.3.3. Workarounds: migrate from the standalone engine API to the Fastify plugin path, where the framework error handler catches the exception.
Articles & Coverage 1
AnalysisAI
Denial of service in @fastify/middie 9.1.0 through 9.3.2 lets remote unauthenticated attackers crash the Node.js process by sending request paths with malformed percent-encoded sequences. The standalone engine's URL normalization step fails to catch a synchronous decoder exception, terminating the process and taking down all connected clients until manual restart. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires that the target application call middie.run directly on the @fastify/middie standalone engine API (versions 9.1.0-9.3.2) - this specific deployment mode is the essential precondition. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H, base 7.5) is credible: exploitation is network-reachable, low-complexity, unauthenticated, requires no user interaction, and impact is availability-only (no confidentiality or integrity loss). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker who can reach an internet-facing Node.js service built on the @fastify/middie standalone engine sends a single HTTP request with a malformed path such as '/foo%' or a truncated multibyte percent sequence. The decoder throws during normalization, the exception escapes middie.run, and the Node process exits - denying service to every connected client until the app is restarted. … |
| Remediation | Vendor-released patch: upgrade to @fastify/middie 9.3.3, which is the primary and recommended fix. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
24 hours: Audit application deployments for @fastify/middie versions 9.1.0-9.3.2; isolate or flag high-risk services for immediate mitigation. …
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Same weakness CWE-248 – Uncaught Exception
View allSame technique Denial Of Service
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External POC / Exploit Code
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