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Part of a larger attack: @posthog published 56 malicious packages. See the full campaign →
Malicious package

@posthog/web-dev-servernpm

Advisory published Updated

@posthog/web-dev-server is a confirmed malicious npm package (MAL-2025-190899) that steals credentials and exfiltrates sensitive data (malicious version 1.0.5). Do not install it — remove it immediately and rotate any exposed credentials.

Malicious code in @posthog/web-dev-server (npm)

MAL-2025-190899
Immediate action
Remove the package, then rotate any secrets the build/runtime could reach.
npm uninstall @posthog/web-dev-server

What this malware does

The package @posthog/web-dev-server was found to contain malicious code.

This package was compromised by the Sha1-Hulud: The Second Coming NPM worm. The malicious payload steals tokens and credentials and publishes them to GitHub. The worm will propogate itself to NPM packages the user owns and establish persistence is a GitHub action. The package may also destroy the user's home directory.

Malicious versions

1 flagged
1.0.5

Indicators of compromise (SHA-256)

0d8d0531931bec7f4add3b4f255b7f6572d28ff3edf2774f7d076fde394eb405
36dda446ca469692c1b804c36a09761b8c9b3ba80d588324bd4fed0579394104

Detection & response playbook

Credential / info stealer

  1. Find it

    Search your lockfiles and build artifacts for @posthog/web-dev-server (version 1.0.5).

  2. If you installed it — respond

    @posthog/web-dev-server 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.

  3. Did it already run?

    If @posthog/web-dev-server 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. @posthog/web-dev-server on npm has been identified as a malicious package (version 1.0.5 flagged). It should be removed immediately — do not install or keep it in your dependency tree.

References

Credits

  • Amazon Inspector · finder

Detect & block this

O3 blocks @posthog/web-dev-server-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

All malware advisories How O3 detects malware Vulnerability database
@posthog/web-dev-server (npm) malicious package — MAL-2025-190899 | O3 Security