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Malicious package

strutil-coreRubyGems

Advisory published Updated

strutil-core is a confirmed malicious RubyGems package (MAL-2026-19054) that steals credentials and exfiltrates sensitive data (malicious version 1.0.1). Do not install it — remove it immediately and rotate any exposed credentials.

Malicious code in strutil-core (RubyGems)

MAL-2026-19054
Immediate action
Remove the package, then rotate any secrets the build/runtime could reach.
gem uninstall strutil-core

What this malware does

strutil-core 1.0.1, presented as "Core string utilities for Ruby", runs its payload at install time from its native-extension step. The step downloads the Bun JavaScript runtime from Bun's GitHub releases into a hidden temporary directory (/tmp/.b_<pid>/) and runs ext/strutil-core/index.js from the installed gem. Observed in a sandboxed gem install strutil-core -v 1.0.1: the script read 51 credential stores belonging to other tools (cloud: AWS, Azure, Google Cloud, Vault; forges: GitHub CLI, GitLab CLI, git credentials, SSH keys; package registries: npm, PyPI, RubyGems, NuGet, Composer, Yarn; Docker and Kubernetes; Claude Code and Codex logins; database client files; cryptocurrency wallets; Terraform, Databricks, Hugging Face, Vercel and Kaggle tokens). It then used them against AWS STS, Secrets Manager and Systems Manager Parameter Store in 18 regions and ECR in 11, Azure Resource Manager and Microsoft Graph, Google Cloud's metadata service and Resource Manager, and the GitHub, GitLab and GitHub Container Registry APIs, and connected to paleasbest.top. It installed persistence as a systemd user service (~/.config/systemd/user/pkg-runtime.service) with ~/.local/share/runtimes/sync.py and a copy of the JavaScript at /.config/index.js, and rewrote the Cursor editor's MCP configuration (/.cursor/mcp.json). paleasbest.top is the server of the pystr-codec PyPI worm (MAL-2026-18432, Miasma family); this appears to be the same worm repackaged as a gem.

Malicious versions

1 flagged
1.0.1

Detection & response playbook

Credential / info stealer

  1. Find it

    Search your lockfiles and build artifacts for strutil-core (version 1.0.1).

  2. If you installed it — respond

    strutil-core 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 strutil-core 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. strutil-core on RubyGems has been identified as a malicious package (version 1.0.1 flagged). It should be removed immediately — do not install or keep it in your dependency tree.

References

Credits

  • Bitbison · finder

Detect & block this

O3 blocks strutil-core-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

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strutil-core (RubyGems) malicious package — MAL-2026-19054 | O3 Security