2025 Substack — ~697K records (Oct 2025, discovered Feb 2026)
Data compromised
Emails, phone numbers, user IDs, names, profile pictures, bios, Stripe IDs
Technical writeup
Substack experienced unauthorized access in October 2025 via system weakness; discovered Feb 3, 2026. Threat actor leaked ~697K-record database on BreachForums Feb 2. Exposed: emails, phone numbers, user IDs, names, profile pictures, bios, account creation dates, social media handles, Stripe IDs. Passwords and financial data not compromised. CEO Chris Best apologized; vulnerability patched.
Root cause
System weakness exploited; delayed detection (~4 months)