CVE-2026-22031@fastify/middie is the plugin that adds middleware support on steroids to Fastify.
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@fastify/middie is the plugin that adds middleware support on steroids to Fastify. A security vulnerability exists in @fastify/middie prior to version 9.1.0 where middleware registered with a specific path prefix can be bypassed using URL-encoded characters (e.g., `/%61dmin` instead of `/admin`). While the middleware engine fails to match the encoded path and skips execution, the underlying Fastify router correctly decodes the path and matches the route handler, allowing attackers to access protected endpoints without the middleware constraints. Version 9.1.0 fixes the issue.
- CVSS
- 8.8 HIGH (v3.1, NVD)CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Weakness (CWE)
- CWE-177
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Not given
- NVD analysis
- Analyzed
- Record last updated
- Jun 17, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
fastify fastify/middie fastify:fastify/middie | before 9.1.0 | NVD |
References
- https://github.com/fastify/middie/commit/d44cd56eb724490babf7b452fdbbdd37ea2effbapatch
- https://github.com/fastify/middie/pull/245issue-tracking, patch
- https://github.com/fastify/middie/releases/tag/v9.1.0product, release-notes
- https://github.com/fastify/middie/security/advisories/GHSA-cxrg-g7r8-w69pexploit, vendor-advisory
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.