Unintended proxy or intermediary in Fastify-reply-from - CVE-2025-66415
Published: December 3, 2025
Vulnerability identifier: #VU119106
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2025-66415
CWE-ID: CWE-441
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: fastify.io
Affected software:
Fastify-reply-from
Fastify-reply-from
Detailed vulnerability description
The vulnerability allows a remote attacker to bypass implemented security restrictions.
The vulnerability exists due to improper input validation when handling the ".." characters in URLs. A remote attacker can use a specially crafted URL to access routes that are not allowed, even though the reply.from is defined for specific routes in @fastify/reply-from.
How to mitigate CVE-2025-66415
Install updates from vendor's website.