9.1

CVE-2026-2880: fastify fastify\/middie Improper Input Validation

CVSS: 9.1v3.1CriticalAnalyzed
AliasesGHSA-8p85-9qpw-fwgw
Published 27-02-2026Last modified 27-02-2026
Open JSON

Vulnerability summary

CVE-2026-2880 is a critical (CVSS 9.1) Improper Input Validation vulnerability in fastify fastify\/middie. EPSS estimates a 0.53% chance of exploitation in the next 30 days, higher than 43.5% of scored vulnerabilities.

Overall risk
70/100
0100
High · default modelHow is this calculated?
CVSS score
9.1/10
010
Critical · v3.1 (NVD)
EPSS score
0.53%
0%100%
Low · +0.14 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Timeline

  1. 27-02-2026
    PublishedVulnerability first disclosed.
  2. 27-02-2026
    Last modifiedVulnerability information updated.

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 metrics

4 scores · 3 sources · 2 versions

EPSS trend

Probability

0.53%

Chance of exploitation in the next 30 days

Percentile

44%

Versus all other CVEs

30-day change

+0.14 pp

From 0.39% on 20-09-2026

20-09-202620-10-2026
EPSS score
0.53%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

@fastify1 product
  • middie< 9.2.0
@fastify/middie1 product
Fastify1 product

3 vendors · 3 products

References

7 links