CVE-2026-220318.4HighCWE-177

CVE-2026-22031: Fastify Middie Middleware Path Bypass

fastify · middie

Affected: fastify middie · Exploitation: unlikely (under 1%)

Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.

0.5%probability of exploitation in the next 30 days

45th percentile

050100

Higher than 45% of scored CVEs

8.4HighCVSS 3.1

LowMediumHighCrit.

DescriptionCVE.org

@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.

Affected products1

From the CVE record. A product or version that is not listed is unknown, not unaffected.

fastify · middie< 9.1.0

On the Atlas

Every published CVE is on the CyberSIXT Atlas, grouped by weakness, vendor and month.

Open the Atlas

Exploitation: Unlikely (under 1%). EPSS under 1%, or no score yet.
CISA KEV: Not listed
Public check: No public nuclei template
Weakness: Improper Handling of URL Encoding (Hex Encoding) · Injection and Smuggling
Vendor: fastify
Published: January 2026
Band: Unlikely (under 1%), January 2026

CoverageNo articles yet

No CyberSIXT article names CVE-2026-22031 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.