Summary

Infostealers replayed stolen Claude session cookies into paid accounts without ever touching the login page two-factor authentication guards. The accounts Anthropic flagged were card-billed, self-serve accounts, which is the population no corporate identity provider governs, and no admin console can sign out. Session-cookie replay bypasses SSO as thoroughly as it bypasses 2FA. What SSO provides here is revocation and visibility, not prevention.

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