# CVE-2025-66415: @fastify/reply-from — Fixed in 12.5.0

📦 npm

Not in CISA KEV

# CVE-2025-66415 — @fastify/reply-from

[Fix: fastify/fastify-reply-from@4d9795c](https://github.com/fastify/fastify-reply-from/commit/4d9795cd5b57a36756d37b7f036eae369f69fa66)

CVE-2025-66415 is a CWE-441 vulnerability in @fastify/reply-from. A fix is available for @fastify/reply-from — see the affected versions and patch details below.

fastify-reply-from bypass of reply forwarding

Also known as[GHSA-2q7r-29rg-6m5h](/vulnerability/GHSA-2q7r-29rg-6m5h)

Published

Dec 1, 2025

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

## Exploitation Status

### No confirmed exploitation observed yet

-   CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2025-66415.

## EPSS Exploitation Probability

[via FIRST.org ↗](https://www.first.org/epss/)

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs9th percentile — riskier than 9% of all scored CVEsHighest risk

0.00%0.23%0.46%0.69%0.0%0.2%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from [FIRST.org EPSS](https://www.first.org/epss/).

## Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

42other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

`@fastify/reply-from`npm

790Kdownloads / week

## Description

#### Summary

By crafting a malicious URL, an attacker could access routes that are not allowed, even though the `reply.from` is defined for specific routes in `@fastify/reply-from`.

#### Details

An attacker can bypass the route defined by the `@fastify/reply-from` package by adding a `..` symbol, which, for `curl` version `8.7.1`, is `%2e%2e`.

#### Impact

Everyone is using this package with the routes option to protect a 3rd-party resource.

## Affected Packages

1 total 1 fixed

Ecosystem

Package

Vulnerable range

Fix

📦npm

`@fastify/reply-from` 

all versions

12.5.0`npm install @fastify/reply-from@12.5.0`

## Affected Products

1 product · 1 configurations

Application

`reply-from`fastify

≤ 12.4.0

range

## Detection & mitigation playbook

Open-source dependency

1.  ### Detect
    
    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @fastify/reply-from, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
    
2.  ### Fix
    
    Update @fastify/reply-from to 12.5.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-66415 is resolved across your whole dependency graph.
    
3.  ### Workarounds
    
    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
    

## Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

This vulnerability is rated Moderate for Red Hat because it allows an attacker to bypass intended route restrictions in applications utilizing the \`fastify-reply-from\` plugin by crafting a malicious URL. This could lead to unauthorized access to specific application routes, potentially exposing sensitive information…

Workaround published by Red Hat

> To mitigate the risk associated with this vulnerability, Red Hat recommends restricting network access to applications utilizing \`fastify-reply-from\` to trusted networks only. Additionally, ensure that any routes intended to be inaccessible via forwarding have robust, independent access control mechanisms in place, separate from the \`fastify-reply-from\` plugin's internal logic. If the \`fastify-reply-from\` functionality is not essential, consider disabling or removing the plugin to eliminate the attack surface.

Source: [Red Hat security advisory for CVE-2025-66415](https://access.redhat.com/security/cve/cve-2025-66415) (CC BY 4.0)

## Frequently Asked Questions

\### Summary By crafting a malicious URL, an attacker could access routes that are not allowed, even though the \`reply.from\` is defined for specific routes in \`@fastify/reply-from\`. ### Details An attacker can bypass the route defined by the \`@fastify/reply-from\` package by adding a \`..\` symbol, which, for \`curl\` version \`8.7.1\`, is \`%2e%2e\`. ### Impact Everyone is using this package with the routes option to protect a 3rd-party resource.

O3 Security · Impact-Aware SCA

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