Which versions of upstart.previewcss are malicious?

The following npm versions of upstart.previewcss are flagged malicious: 99.99.1. Treat any of these as compromised.

How do I remediate upstart.previewcss if I installed it?

upstart.previewcss 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 upstart.previewcss — how do I know if it already compromised me?

If upstart.previewcss 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 upstart.previewcss part of a known attack campaign?

Yes — upstart.previewcss is associated with the GHSA-g8xh-53qm-mc7m 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 upstart.previewcss 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 upstart.previewcss (version 99.99.1). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging upstart.previewcss across your stack and pipelines.

Malicious package

upstart.previewcssnpm

Malicious code in upstart.previewcss (npm) Remove it immediately and rotate any exposed credentials.

MAL-2026-2614

Immediate action

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

npm uninstall upstart.previewcss

What this malware does

Package is malware. It collects and exfiltrates sensitive data (SSH keys, credentials, environment variables) and system info to a remote server.

The package upstart.previewcss was found to contain malicious code.

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.

The OpenSSF Package Analysis project identified 'upstart.previewcss' @ 99.99.1 (npm) as malicious.

It is considered malicious because:

The package executes one or more commands associated with malicious behavior.

Malicious versions

1 flagged

99.99.1

Indicators of compromise (SHA-256)

87acedd73a33ae92010aa1794c9d1a669848ca7a05e613c5a69affe4f8e34ecc

ae6e996bd3c6be34c03d1504ffa7df8631d9b69a954be1bba08154b59dc4115c

bd2d5c329f24c54ca68ce21884867d6b4db6ae64d0e2041af60deb2203cc8830

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 upstart.previewcss (version 99.99.1). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging upstart.previewcss across your stack and pipelines.
If you installed it — respond
upstart.previewcss 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 upstart.previewcss 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 upstart.previewcss 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. upstart.previewcss on npm has been identified as a malicious package (version 99.99.1 flagged). It should be removed immediately — do not install or keep it in your dependency tree.

Campaign

GHSA-g8xh-53qm-mc7m

References

Credits

Amazon Inspector · finder
OpenSSF: Package Analysis · finder
SafeDep · finder

Detect & block this

O3 blocks upstart.previewcss-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