Critical severity · published Feb 27, 2026
CVE-2026-2880
@fastify/middie has an improper path normalization vulnerability
9.1
CVSS
0.4%
EPSS
No
On KEV
Description
A vulnerability in @fastify/middie versions < 9.2.0 can result in authentication/authorization bypass when using path-scoped middleware (for example, app.use('/secret', auth)).
When Fastify router normalization options are enabled (such as ignoreDuplicateSlashes, useSemicolonDelimiter, and related trailing-slash behavior), crafted request paths may bypass middleware checks while still being routed to protected handlers.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 37% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
FA
@fastify/middie · @fastify/middie
0.0.0 before 9.2.0 · source: vendor
FA
Fastify/middie · Fastify
before 9.2.0 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-2880
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-2880
Mitigation
https://github.com/fastify/middie/security/advisories/GHSA-8p85-9qpw-fwgw
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