Cyber Resilience

CVE-2026-6414

Fastify-Static 8.0.0 – 9.1.1

Published
16 April 2026
Modified
23 April 2026
Patch / advisory
View advisory
CVSS Score v3.1 5.9
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
EPSS Score 0.0041 34th percentile
Risk Priority 46 floored blend · peak EPSS

Summary

CVE-2026-6414 is a medium-severity Hex Encoding (CWE-177) vulnerability in Fastify Fastify-Static. Its CVSS base score is 5.9 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 34th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SI-10 (Information Input Validation) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

@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…

more

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 this issue. There are no workarounds.

CWE(s)
CWE-177

Related Threats

MITRE ATT&CK Enterprise Techniques

T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-6410Same product: Fastify Fastify-Static
CVE-2026-15074Same product: Fastify Fastify-Static
CVE-2026-7120Same product: Fastify Fastify-Static
CVE-2026-22031Same vendor: Fastify
CVE-2023-27495Same vendor: Fastify
CVE-2023-31999Same vendor: Fastify
CVE-2023-51701Same vendor: Fastify
CVE-2026-15631Same vendor: Fastify
CVE-2026-41041Shared CWE-177
CVE-2026-33805Same vendor: Fastify

Affected Assets

fastify
fastify-static
8.0.0 — 9.1.1

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V1.2.2

Mitigating Controls (NIST 800-53 r5) AI

SI-10 Information Input Validation good match

Proper input validation requires decoding and checking URL-encoded data before use, directly stopping the weakness from being exploitable.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly require correct URL-encoding/decoding and input validation during development.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing in development catches URL-decoding flaws before release, but does not itself define coding rules.

A.8.25 Secure development life cycle partial match
prevents

Secure SDLC processes include validation steps that reduce CWE-177, yet the control is broader than this single weakness.

A.8.26 Application security requirements partial match
prevents

Application security requirements explicitly call for input validation and canonicalization, directly preventing improper URL decoding.

A.8.28 Secure coding partial match
prevents

Secure coding standards mandate proper handling and decoding of encoded inputs, eliminating CWE-177.

References