PatchTheCVECVE-2026-14198: @fastify/middie versions 9.1.0 through 9.3.2 decode the encoded slash %2F inside path parameter values before
CVE-2026-14198 is a critical-severity flaw (CVSS 9.1) affecting fastify\/middie. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
@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 pat
Why this priority
- Critical severity
- Remotely exploitable, no login, no user action
A fixed release or distro patch exists.
Risk facts
| CVSS score | 9.1 (Critical) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 0.5% (top 56%) |
| CISA exploited list | No |
| Weakness | CWE-436 |
| Published | 2026-07-01 |
| Last modified | 2026-07-02 |
Last updated 2026-07-02 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2026-14198?
fastify\/middie: upgrade to 9.3.3. Exact commands for each OS are on this page.
Is CVE-2026-14198 being exploited?
CVE-2026-14198 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2026-14198 affect?
CVE-2026-14198 affects fastify\/middie. Severity is critical (CVSS 9.1). @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 o
How urgent is CVE-2026-14198?
Priority 48/100. Critical severity; Remotely exploitable, no login, no user action
Related CVEs
- CVE-2026-85184 CRITICAL 9.1 UPGRADE @fastify/middie versions >= 9.1.0 and before 9.3.4 decide whether to run path-scoped middleware by matching ag
- CVE-2026-14181 HIGH 7.5 UPGRADE @fastify/middie versions 9.1.0 through 9.3.2 fail to guard the URL normalization step used by the standalone e