CVE-2026-14181 json
@fastify/middie standalone engine vulnerable to Denial of Service via malformed percent-encoded paths
published 4mo ago modified 4mo ago also EUVD-2026-40947
- cvss
- 7.5
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.5%
- EPSS 0.5% chance of exploitation in 30 days, percentile 43%
- public exploits
- 0
- none known
Summary
@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.
Patch / fix
- @fastify/middie @fastify/middie 9.3.3
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Check with FencerCISA SSVC
- Exploitation
- none
- Automatable
- yes
- Technical impact
- partial
- Assessed
- 4mo ago
Exploit prediction
0.50% chance of exploitation in the next 30 days, higher than 43% of all scored CVEs (FIRST EPSS, 2026-11-09).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
Affected products
- @fastify/middie @fastify/middie
Classification
- Weakness
-
- CWE-248 Uncaught Exception
References
-
github.com
/fastify/middie/security/advisories/GHSA-qcc9-jh8q-47vh
mitigation, vendor-advisory
-
cna.openjsf.org
/security-advisories.html
vendor-advisory
Sources
- CVE List CVE-2026-14181
- NVD CVE-2026-14181
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