test-pkg-yarnnpm
test-pkg-yarn is a confirmed malicious npm package (MAL-2026-6718) that steals credentials and exfiltrates sensitive data (malicious versions 1.0.0, 1.0.1, 1.0.2). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in test-pkg-yarn (npm)
What this malware does
package.json declares bin: { "node": "./shim.js" }, causing npm/yarn to symlink node in node_modules/.bin (and in a system bin dir on global install) to a package-controlled script. Subsequent invocations of node resolved through that PATH entry execute shim.js instead of the real Node.js runtime, redirecting any tooling that expects node to attacker-controlled code. In addition, scripts.postinstall runs bun shim.js || node shim.js, and shim.js unconditionally invokes OS commands at install time via child_process.execSync — spawning a GUI calculator (calc on Windows, gnome-calculator on Linux, open -a Calculator on macOS), opening a URL in the user's browser, and writing a marker file to /tmp/.bun-npm-pwned. The package self-identifies as 'BunnyHijack PoC - yarn variant' with the console message '[!] PATH POISONED - test-pkg-yarn just hijacked your node command.' Although framed as a proof-of-concept and not currently exfiltrating data, the behavior is real install-time code execution against any developer who installs the package and a persistent hijack of the node command in PATH.
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
Indicators of compromise (SHA-256)
Detection & response playbook
Credential / info stealerFind it
Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for test-pkg-yarn (3 malicious versions). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging test-pkg-yarn across your stack and pipelines.
If you installed it — respond
test-pkg-yarn 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 test-pkg-yarn 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 test-pkg-yarn 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
Campaign
References
Credits
- Amazon Inspector · finder
Detect & block this
O3 blocks test-pkg-yarn-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.