Malicious code in preinstall-hook-webhook-callback-demo (npm)
The npm package preinstall-hook-webhook-callback-demo contained malicious code in its preinstall lifecycle script that automatically contacts webhook.site, an attacker-controlled exfiltration endpoint, upon installation. This enables data exfiltration and callback beaconing at install time without user interaction.
- Disclosed
- Last updated
- Blast radius
- All npm users who installed preinstall-hook-webhook-callback-demo
- Ecosystems
- Attack vectors
- Affected entities
- preinstall-hook-webhook-callback-demonpm package with malicious preinstall script
The npm package preinstall-hook-webhook-callback-demo was found to contain malicious code embedded in its package.json preinstall lifecycle script. The script automatically executes when users run npm install, before any user interaction occurs.
The preinstall hook is configured to contact webhook.site, an ephemeral request-capture service commonly used as an attacker-controlled exfiltration sink. webhook.site is not a legitimate, documented, or first-party destination for any legitimate build or runtime purpose of this package.
The combination of an auto-executing preinstall script wired to an out-of-band capture endpoint represents a classic installer-side data exfiltration and callback beaconing attack pattern. This allows attackers to exfiltrate data or establish command-and-control callbacks at the moment of package installation.
The incident was identified and credited to the OpenSSF malicious-packages project, which maintains a catalog of confirmed malicious packages across package ecosystems.
Indicators of compromise
- Packages
- preinstall-hook-webhook-callback-demo
- Domains
- webhook.site
Remediation
- Remove preinstall-hook-webhook-callback-demo from all projects and dependencies
- Audit npm install logs and environment for any suspicious network connections to webhook.site or similar exfiltration endpoints
- Review any systems where this package was installed for signs of data exfiltration or unauthorized access
- Use npm audit to identify if this package is present in any project dependencies
- Consider implementing npm package signature verification and allowlisting to prevent installation of malicious packages
Sources
- GitHub Advisory GHSA-9j5p-xwfm-m987 · GitHub Advisory Database
Cite this entry
"Malicious code in preinstall-hook-webhook-callback-demo (npm)." supplychainattack.org, Supply Chain Attack Incident Catalog. Disclosed August 14, 2026; last updated August 14, 2026. https://supplychainattack.org/incident/malicious-code-in-preinstall-hook-webhook-callback-demo-npm-1vepbj
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