CVE-2025-66415Network attack vector

Unauthorized upstream access via encoded path traversal

Published Dec 1, 2025 · Updated Dec 2, 2025

Route restriction bypass in Fastify @fastify/reply-from before 12.5.0 allows remote attackers to reach disallowed upstream routes. The buildURL helper accepted literal or percent-encoded '..' path segments and resolved them against the configured base without rejecting traversal. Exposure requires an application that uses reply.from to protect an upstream resource, and successful requests can read or alter that resource within the proxy's authority.

CVSS severity6.9
Medium
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Route restriction bypass in Fastify @fastify/reply-from before 12.5.0 allows remote attackers to reach disallowed upstream routes. The buildURL helper accepted literal or percent-encoded '..' path segments and resolved them against the configured base without rejecting traversal. Exposure requires an application that uses reply.from to protect an upstream resource, and successful requests can read or alter that resource within the proxy's authority.

The record

CVE
CVE-2025-66415
Published
Dec 1, 2025
Updated
Dec 2, 2025
Vendor
Fastify
Product
@fastify/reply-from
Classifications
CWE-441, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 1, 2025CVE publishedPublication date reported by the CVE source.
  2. Dec 2, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 12.5.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Fastify · @fastify/reply-fromversion=< 12.5.0

Published CVSS scores

6.9GitHub CNACVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-441Unintended Proxy or Intermediary ('Confused Deputy')
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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