PT-2026-22377 · Fastify · @Fastify/Middie

Cristian Vargas + 1 · Published 2026-02-27 · Updated 2026-02-28 · CVE-2026-2880

Positive Technologies (AI Summary)

CVSS v3.1

9.1

Critical

Base vector

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Name of the Vulnerable Software and Affected Versions @fastify/middie versions prior to 9.2.0

Description A flaw exists in @fastify/middie that can lead to authentication or authorization bypass when path-scoped middleware is used, such as with app.use('/secret', auth). This occurs when Fastify router normalization options are enabled, including options like ignoreDuplicateSlashes, useSemicolonDelimiter, and trailing-slash behavior. Specifically, specially crafted request paths may circumvent middleware checks while still reaching protected handlers.

Recommendations Update @fastify/middie to version 9.2.0 or later.

Fix

RCE

Weakness Enumeration

CWE-20

Related Identifiers

CVE-2026-2880

GHSA-8P85-9QPW-FWGW

Affected Products

@Fastify/Middie

References · 12

• https://github.com/fastify/middie/security/advisories/GHSA-8p85-9qpw-fwgw · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-2880 · Security Note
• https://osv.dev/vulnerability/GHSA-8p85-9qpw-fwgw · Vendor Advisory
• https://osv.dev/vulnerability/CVE-2026-2880 · Vendor Advisory
• https://github.com/fastify/middie · Note
• https://github.com/fastify/middie/releases/tag/v9.2.0 · Note
• https://github.com/fastify/middie/commit/140e0dd0359d890fec7e6ea1dcc5134d6bd554d4 · Note
• https://fluidattacks.com/advisories/jimenez · Note
• https://fluidattacks.com/advisories/policy · Note
• https://t.me/CVEtracker/46008 · Telegram Post
• https://twitter.com/kom_256/status/2027452843578249266 · Twitter Post
• https://twitter.com/CVEnew/status/2027466583711551787 · Twitter Post