CVE-2026-14181: @fastify/middie versions 9.1.0 through 9.3.2 fail to guard the URL normalization step used by the standalone e

Q: How do I fix CVE-2026-14181?

fastify\/middie: upgrade to 9.3.3. Exact commands for each OS are on this page.

Q: Is CVE-2026-14181 being exploited?

CVE-2026-14181 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-2026-14181 affect?

CVE-2026-14181 affects fastify\/middie. Severity is high (CVSS 7.5). @fastify/middie versions 9.1.0 through 9.3.2 fail to guard the URL normalization step used by the standalone engine when incoming request paths contain malformed percent-encoded sequences. Inputs such as an incomplete percent escape or a tr

Q: How urgent is CVE-2026-14181?

Priority 42/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 7.5REMOTEUPGRADE

CVE-2026-14181 is a high-severity flaw (CVSS 7.5) 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 through 9.3.2 fail to guard the URL normalization step used by the standalone engine when incoming request paths contain malformed percent-encoded sequences. Inputs such as an incomplete percent escape or a truncated multibyte sequence cause the underlying decoder to throw synchronously, and the exception escapes the middie normalize step and terminates the Node.js process. The bypass affects applications that call

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 57%)
CISA exploited list	No
Weakness	CWE-248
Published	2026-07-01
Last modified	2026-07-02

Publisher (CNA): openjs · Vendor: fastify

Last updated 2026-07-02 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-01 12:16 UTCPublished CVE record published
2026-07-02 13:50 UTCUpdated Record last modified

fastify fastify\/middie UPGRADE

Affected: >= 9.1.0 and < 9.3.3

Fixed in: 9.3.3

Safe to downgrade to: a release before 9.1.0

1. Check installed version

npm ls fastifymiddie

2. UPGRADE to 9.3.3

npm install fastifymiddie@">=9.3.3"

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-2026-14181?

fastify\/middie: upgrade to 9.3.3. Exact commands for each OS are on this page.

Is CVE-2026-14181 being exploited?

CVE-2026-14181 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-2026-14181 affect?

CVE-2026-14181 affects fastify\/middie. Severity is high (CVSS 7.5). @fastify/middie versions 9.1.0 through 9.3.2 fail to guard the URL normalization step used by the standalone engine when incoming request paths contain malformed percent-encoded sequences. Inputs such as an incomplete percent escape or a tr

How urgent is CVE-2026-14181?

Priority 42/100. High severity; Remotely exploitable, no login, no user action

Software pages

Node.js vulnerabilities

Related CVEs

CVE-2026-85184 CRITICAL 9.1 UPGRADE @fastify/middie versions >= 9.1.0 and before 9.3.4 decide whether to run path-scoped middleware by matching ag
CVE-2026-14198 CRITICAL 9.1 UPGRADE @fastify/middie versions 9.1.0 through 9.3.2 decode the encoded slash %2F inside path parameter values before

References

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