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Vulnerabilities

Security fix · CVE-2026-112712

@fastify/middie is the Express-style middleware engine for Fastify.

Published Oct 20, 2026 · catalog updated Oct 22, 2026 · @fastify/middie is the Express-style

Last checked Nov 7, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-112712. EPSS is 0.31%. Act only if a listed version of @fastify/middie is the Express-style is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (@fastify/middie is the Express-style).
  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Critical9.1
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.31%
Remediation
Advisory link
Affected products
package npm

@fastify/middie is the Express-style middleware engine for Fastify. In versions from 9.0.0 through 9.3.5, the use() function joined a path-scoped middleware's mount path to the plugin scope prefix in a way that could diverge from the path Fastify's router serves, most often when the scope prefix ended in a slash, and also for array mount paths and for mount paths written without a leading slash. When the two paths disagreed, the middleware was silently skipped while the route handler still ran, so path-scoped middleware such as authentication, authorization, or rate limiting could be bypassed by a single unauthenticated request. The issue is fixed in @fastify/middie 9.3.6, and users should upgrade to 9.3.6 or later. As a workaround, enforce authorization in a Fastify hook such as preHandler that runs after the router has resolved the request.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • package npmversion unspecified

How to fix CVE-2026-112712

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-112712. EPSS is 0.31%. Act only if a listed version of @fastify/middie is the Express-style is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-436. EPSS 0.31%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 20, 2026 · NIST NVD

    Detected

    @fastify/middie is the Express-style middleware engine for Fastify. In versions from 9.0.0 through 9.3.5, the use() function joined a path-scoped middleware's mount path to the plugin scope prefix in a way that could diverge from the path Fastify's router serves, most often when the scope prefix ended in a slash, and also for array mount paths and for mount paths written without a leading slash. W

  2. Oct 22, 2026 · NIST NVD

    Updated

    @fastify/middie is the Express-style middleware engine for Fastify. In versions from 9.0.0 through 9.3.5, the use() function joined a path-scoped middleware's mount path to the plugin scope prefix in a way that could diverge from the path Fastify's router serves, most often when the scope prefix ended in a slash, and also for array mount paths and for mount paths written without a leading slash. W

Sources

  • CVE.orgVulnerability recordCVE-2026-112712

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-112712

    30-day exploitation probability 0.31%

    first.org
  • NIST NVDVulnerability recordCVE-2026-112712

    @fastify/middie is the Express-style middleware engine for Fastify. In versions from 9.0.0 through 9.3.5, the use() function joined a path-scoped middleware's mount path to the plugin scope prefix in a way that could diverge from the path Fastify's router serves, most often when

    nvd.nist.gov
  • Snyk Vulnerability DatabasePackage advisorySNYK-JS-FASTIFYMIDDIE-21431600

    Interpretation Conflict

    security.snyk.io

References

Freshness

Last verified in this catalog Nov 7, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • Snyk Vulnerability DatabaseOct 25, 2026
  • CVE.orgOct 23, 2026
  • FIRST EPSSOct 23, 2026
  • NIST NVDOct 22, 2026