How severe is CVE-2025-66415?

No CVSS score has been assigned to CVE-2025-66415 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2025-66415?

CVE-2025-66415 affects the following packages: @fastify/reply-from (npm). Ecosystems affected: npm.

How do I fix CVE-2025-66415?

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.

How do I detect CVE-2025-66415 in my npm dependencies?

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.

How do I mitigate CVE-2025-66415 if there is no patch (or I can't update yet)?

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.

How does O3 Security protect against CVE-2025-66415?

O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-66415 can be triaged on real exposure rather than presence alone.

Is CVE-2025-66415 actively exploited in the wild?

No public exploit code has been indexed for CVE-2025-66415 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2025-66415?

CVE-2025-66415 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 7th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2025-66415?

CVE-2025-66415 is classified as CWE-441 (CWE-441). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2025-66415 published, and has it been updated?

CVE-2025-66415 was published on December 1, 2025 and was last updated on August 12, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

CVE-2025-66415 — @fastify/reply-from

Fix: fastify/fastify-reply-from@4d9795c

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 asGHSA-2q7r-29rg-6m5h

Published

Dec 1, 2025

Updated

Aug 12, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Sep 24, 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 ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs7th percentile — riskier than 7% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

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.

39other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

@fastify/reply-fromnpm

308Kdownloads / 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`

Detection & mitigation playbook

Open-source dependency

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.
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.
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.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-66415 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2025-66415. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

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

Is CVE-2025-66415 in your dependencies?

O3 Security finds CVE-2025-66415 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

Scan my dependencies How O3 SCA works