Domain Validation Bypass Allows Automatic Requests to Attacker-Controlled Domains

High7.1CVE-2026-24052 · Published Feb 3, 2026

Claude Code contained insufficient URL validation in its trusted domain verification mechanism for WebFetch requests. The application used a `startsWith()` function to validate trusted domains (e.g., `docs.python.org`, `modelcontextprotocol.io`), this could have enabled attackers to register domains like `modelcontextprotocol.io.example.com` that would pass validation. This could enable automatic requests to attacker-controlled domains without user consent, potentially leading to data exfiltration. Users on standard Claude Code auto-update have received this fix already. Users performing manual updates are advised to update to the latest version. Thank you to hackerone.com/47sid-praetorian for reporting this issue!