CVE-2026-6270 json
@fastify/middie vulnerable to middleware authentication bypass in child plugin scopes
published 6mo ago modified 4mo ago also EUVD-2026-23241 , GHSA-72c6-fx6q-fr5w
- cvss
- 9.1
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.5%
- EPSS 0.5% chance of exploitation in 30 days, percentile 43%
- public exploits
- 0
- none known
Summary
@fastify/middie versions 9.3.1 and earlier do not register inherited middleware directly on child plugin engine instances. When a Fastify application registers authentication middleware in a parent scope and then registers child plugins with @fastify/middie, the child scope does not inherit the parent middleware. This allows unauthenticated requests to reach routes defined in child plugin scopes, bypassing authentication and authorization checks. Upgrade to @fastify/middie 9.3.2 to fix this issue. There are no workarounds.
Patch / fix
- npm @fastify/middie 9.3.2
- @fastify/middie @fastify/middie 9.3.2
Is CVE-2026-6270 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.
Check with FencerCISA SSVC
- Exploitation
- Proof of concept is public
- Automatable
- no
- Technical impact
- total
- Assessed
- 6mo ago
Exploit prediction
0.50% chance of exploitation in the next 30 days, higher than 43% of all scored CVEs (FIRST EPSS, 2026-11-11).
Exploits and checks
- github.com https://github.com/fastify/fastify-express/security/advisories/GHSA-hrwm-hgmj-7p9c referenced PoC, tagged "exploit" by a source, unverified
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 9.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N |
| GitHub | 3.1 | 9.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| npm | @fastify/middie | <9.3.2 |
9.3.2 |
Affected products
- @fastify/middie @fastify/middie
Classification
- Weakness
-
- CWE-436 Interpretation Conflict
References
-
github.com
/fastify/fastify-express/security/advisories/GHSA-hrwm-hgmj-7p9c
web, exploit, mitigation, vendor-advisory
-
github.com
/fastify/middie/security/advisories/GHSA-72c6-fx6q-fr5w
web, vendor-advisory, advisory
-
cna.openjsf.org
/security-advisories.html
web, vendor-advisory
-
nvd.nist.gov
/vuln/detail/CVE-2026-6270
advisory
-
github.com
/fastify/middie
package
Sources
- CVE List CVE-2026-6270
- GitHub Advisory GHSA-72c6-fx6q-fr5w
- NVD CVE-2026-6270
- Maintainer advisory GHSA-72c6-fx6q-fr5w
Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.
The maintainers of fastify/middie published their own advisory on GitHub. Reviewed sources take precedence over it.