@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.
CVE-2026-22031
This high-severity CVE scores 8.4 under NVD CVSS v3. EPSS exploit probability: 0.1%, top 66% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).
- High severity, but no confirmed exploitation yet
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 8.4
- EG Score
- 8.4(medium)
- EPSS
- 37.2%
- KEV
- Not listed
Published
January 19, 2026
Last Modified
May 14, 2026
Advisory Details (4)
Auto-updated May 14, 2026Fastify Middie Middleware Path Bypass · Advisory · fastify/middie · GitHub
https://github.com/fastify/middie/security/advisories/GHSA-cxrg-g7r8-w69pRelease v9.1.0 · fastify/middie · GitHub
https://github.com/fastify/middie/releases/tag/v9.1.0fix: decode paths before matching by kamilmysliwiec · Pull Request #245 · fastify/middie · GitHub
https://github.com/fastify/middie/pull/245fix: decode paths before matching (#245) · fastify/middie@d44cd56 · GitHub
https://github.com/fastify/middie/commit/d44cd56eb724490babf7b452fdbbdd37ea2effbaAffected Packages
(1 across 1 ecosystem)
npm(1)
| Package | Vulnerable range | Fixed in | Dependents |
|---|---|---|---|
| @fastify/middie | — | 9.1.0 | — |
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 12× in last 7d / 46× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
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Frequently asked(5)
What is CVE-2026-22031?
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Dependency Blast Radius
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