Which versions of fastify-addone are malicious?

The following npm versions of fastify-addone are flagged malicious: 5.1.0, 5.1.1. Treat any of these as compromised.

How do I remediate fastify-addone if I installed it?

Remove fastify-addone from your project and lockfile, then assume any secrets accessible to the build or runtime were exposed: rotate API keys, tokens, and credentials, and audit for unexpected outbound activity or persistence.

I already installed fastify-addone — how do I know if it already compromised me?

If fastify-addone was installed, its post-install payload may already have run. Removing the package does not undo that — check outbound connections and credential use from the install window onward.

Is fastify-addone part of a known attack campaign?

Yes — fastify-addone is associated with the IN-MAL-2026-009582, IN-MAL-2026-009762 campaign. Packages in the same campaign often share infrastructure and payloads, so check whether any related packages are also in your dependency tree.

How do I find fastify-addone across my projects, lockfiles, and CI pipelines?

Search your lockfiles and build artifacts for fastify-addone (2 malicious versions).

Malicious package

fastify-addonenpm

Advisory published Jul 9, 2026Updated Jul 12, 2026

fastify-addone is a confirmed malicious npm package (MAL-2026-10098) that executes malicious code on install (malicious versions 5.1.0, 5.1.1). Do not install it — remove it immediately and rotate any exposed credentials.

Malicious code in fastify-addone (npm)

MAL-2026-10098

Immediate action

Remove the package, then rotate any secrets the build/runtime could reach.

npm uninstall fastify-addone

What this malware does

The package presents itself as fastify-plugin (name fastify-addone, repository/homepage/bugs fields point at fastify/fastify-plugin) and copies that project's source with a malicious statement inserted. lib/getPluginName.js contains a top-level statement that base64-decodes a URL via atob, fetches the JSON at https://www.jsonkeeper.com/b/HDXPP, and passes the returned content field to eval. This executes attacker-controlled JavaScript in the caller's process on any require('fastify-addone') (directly or via plugin.js). The destination is an anonymous, mutable third-party JSON-hosting service — not the publisher's infrastructure — and the payload URL is hidden behind base64 to evade casual review.

Malicious versions

2 flagged

5.1.05.1.1

Indicators of compromise (SHA-256)

21b9e477cff478ab071039c18c3adb6577a07cc1d82687b9e7d7cd2594dc9ddf

d2f2c8dc9b9c037bb1da062c060c8e622e400cf24e7d593c1232d4003b867d84

Detection & response playbook

Malicious package

Find it
Search your lockfiles and build artifacts for fastify-addone (2 malicious versions).
If you installed it — respond
Remove fastify-addone from your project and lockfile, then assume any secrets accessible to the build or runtime were exposed: rotate API keys, tokens, and credentials, and audit for unexpected outbound activity or persistence.
Did it already run?
If fastify-addone was installed, its post-install payload may already have run. Removing the package does not undo that — check outbound connections and credential use from the install window onward.

Frequently asked questions

No. fastify-addone on npm has been identified as a malicious package (versions 5.1.0, 5.1.1 flagged). It should be removed immediately — do not install or keep it in your dependency tree.

Campaign

IN-MAL-2026-009582IN-MAL-2026-009762

References

Credits

Amazon Inspector · finder

Detect & block this

O3 blocks fastify-addone-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the malicious outbound activity and severs the channel.

Malware detection Runtime egress monitoring

Explore

All malware advisories How O3 detects malware Vulnerability database