CVE-2026-85184: @fastify/middie versions >= 9.1.0 and before 9.3.4 decide whether to run path-scoped middleware by matching ag

Q: How do I fix CVE-2026-85184?

fastify\/middie: upgrade to 9.3.4. Exact commands for each OS are on this page.

Q: Is CVE-2026-85184 being exploited?

CVE-2026-85184 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-85184 affect?

CVE-2026-85184 affects fastify\/middie. Severity is critical (CVSS 9.1). @fastify/middie versions >= 9.1.0 and before 9.3.4 decide whether to run path-scoped middleware by matching against the raw request target, while the Fastify router resolves an absolute-form request target to its path before dispatching. Be

This month

CRITICAL 9.1REMOTEUPGRADE

CVE-2026-85184 is a critical-severity flaw (CVSS 9.1) affecting fastify\/middie. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

@fastify/middie versions >= 9.1.0 and before 9.3.4 decide whether to run path-scoped middleware by matching against the raw request target, while the Fastify router resolves an absolute-form request target to its path before dispatching. Because the two layers evaluate different strings, a request using an absolute-form target reaches the route handler while the path-scoped middleware, such as authentication or authorization, is skipped. An unaut

Why this priority

Critical severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.1 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 56%)
CISA exploited list	No
Weakness	CWE-436
Published	2026-09-04
Last modified	2026-09-15

Publisher (CNA): openjs · Vendor: fastify

Last updated 2026-09-15 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-04 10:17 UTCPublished CVE record published
2026-09-15 20:02 UTCUpdated Record last modified

fastify fastify\/middie UPGRADE

Affected: >= 9.1.0 and < 9.3.4

Fixed in: 9.3.4

Safe to downgrade to: a release before 9.1.0

1. Check installed version

npm ls fastifymiddie

2. UPGRADE to 9.3.4

npm install fastifymiddie@">=9.3.4"

3. If no update is available yet, DOWNGRADE to a release before 9.1.0

npm view fastifymiddie versions npm install fastifymiddie@"<9.1.0"

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-85184?

fastify\/middie: upgrade to 9.3.4. Exact commands for each OS are on this page.

Is CVE-2026-85184 being exploited?

CVE-2026-85184 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-85184 affect?

CVE-2026-85184 affects fastify\/middie. Severity is critical (CVSS 9.1). @fastify/middie versions >= 9.1.0 and before 9.3.4 decide whether to run path-scoped middleware by matching against the raw request target, while the Fastify router resolves an absolute-form request target to its path before dispatching. Be

How urgent is CVE-2026-85184?

Priority 48/100. Critical severity; Remotely exploitable, no login, no user action

References

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