CVE-2026-6414: @fastify/static versions 8.0.0 through 9.1.0 decode percent-encoded path separators (%2F) before filesystem re

Routine

MEDIUM 5.9REMOTEUPGRADE

CVE-2026-6414 is a medium-severity flaw (CVSS 5.9) affecting fastify-static. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

@fastify/static versions 8.0.0 through 9.1.0 decode percent-encoded path separators (%2F) before filesystem resolution, while Fastify's router treats them as literal characters. This mismatch allows attackers to bypass route-based middleware or guards that protect files served by @fastify/static. For example, a route guard on a protected path can be circumvented by encoding the path separator in the URL. Upgrade to @fastify/static 9.1.1 to fix th

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 64%)
CISA exploited list	No
Weakness	CWE-177
Published	2026-04-16
Last modified	2026-06-17

Publisher (CNA): openjs · Vendor: fastify

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-16 13:16 UTCPublished CVE record published
2026-06-17 11:00 UTCUpdated Record last modified

fastify fastify-static UPGRADE

Affected: >= 8.0.0 and < 9.1.1

Fixed in: 9.1.1

Safe to downgrade to: a release before 8.0.0

1. Check installed version

apt-cache policy fastify-static || rpm -q fastify-static || fastify-static --version

2. UPGRADE to 9.1.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade fastify-static

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade fastify-static

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 8.0.0 (Debian / Ubuntu)

apt-cache madison fastify-static sudo apt install fastify-static=<VERSION_BEFORE_8.0.0> sudo apt-mark hold fastify-static

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list fastify-static sudo dnf downgrade fastify-static-<VERSION_BEFORE_8.0.0> sudo dnf versionlock add fastify-static

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-2026-6414?

fastify-static: upgrade to 9.1.1. Exact commands for each OS are on this page.

Is CVE-2026-6414 being exploited?

CVE-2026-6414 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-2026-6414 affect?

CVE-2026-6414 affects fastify-static. Severity is medium (CVSS 5.9). @fastify/static versions 8.0.0 through 9.1.0 decode percent-encoded path separators (%2F) before filesystem resolution, while Fastify's router treats them as literal characters. This mismatch allows attackers to bypass route-based middlewar

How urgent is CVE-2026-6414?

Priority 35/100. Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-18427 HIGH 7.5 UPGRADE @fastify/static before version 10.1.3 contains an incomplete fix for a previous route guard bypass
CVE-2026-7120 MEDIUM 5.3 UPGRADE @fastify/static evaluates the allowedPath callback before normalizing dot segments and duplicate path separato
CVE-2026-15074 HIGH 7.5 UPGRADE @fastify/static up to and including version 10.1.0 fails to reject dot-dot path segments in request pathnames
CVE-2026-6410 MEDIUM 5.3 UPGRADE @fastify/static versions 8.0.0 through 9.1.0 allow path traversal when directory listing is enabled via the li

References

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