claude-internal-utilsnpm
Advisory published Updated
claude-internal-utils is a confirmed malicious npm package (MAL-2026-4525) that steals credentials and exfiltrates sensitive data (malicious version 9.0.5). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in claude-internal-utils (npm)
What this malware does
Package name impersonates an internal Anthropic 'claude-*' namespace and the description field self-identifies as 'Alex Birsan Style' dependency-confusion bait. The package ships no library code; its only effect is a postinstall lifecycle hook that runs an inline node one-liner which fetches the installer's public IP from api.ipify.org, executes id || ver && whoami && hostname via child_process.exec, and POSTs hostname, cwd, USERDOMAIN/COMPANY env vars, public IP, package name, and the command output as JSON to a hardcoded attacker subdomain at lszakfghwnvxspyfcmaabd1css99rnq3w.oast.fun (an out-of-band interaction service commonly used for exfiltration). Fires automatically on npm install, before any consumer code runs.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Credential / info stealerFind it
Search your lockfiles and build artifacts for claude-internal-utils (version 9.0.5).
If you installed it — respond
claude-internal-utils 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 claude-internal-utils 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
Campaign
References
Credits
- Amazon Inspector · finder
- ReversingLabs · finder
Detect & block this
O3 blocks claude-internal-utils-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.