Impact & Downstream Threats
This breach carries moderate risk due to the nature of exposed data fields and the scale of affected records.
- SIM swap attacks where phone numbers are present
- Targeted phishing campaigns using exposed email addresses
Breach Intelligence
Executive Summary
In October 2025, the publishing platform Substack suffered a data breach that was subsequently circulated more widely in February 2026. The breach exposed 663k account holder records containing email addresses along with publicly visible profile information from Substack accounts, such as publication names and bios. A subset of records also included phone numbers.
About Substack
Publishing and newsletter platform for writers and creators.
Data Points Exposed
Dark Web Verification
Status: Confirmed
- Dataset containing approximately 663K records identified in breach intelligence sources.
- The data is indexed and searchable across breach notification platforms.
Recommended Actions
⚠️ Do not assume this is low sensitivity.
Non-clients may request a breach impact review.
Frequently Asked Questions
In October 2025, Substack experienced a data breach that exposed approximately 663K records containing personal information.
The exposed data includes fields such as email address, phone number.
Approximately 663K records were affected based on current breach intelligence.
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ObscureIQ Advisory
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- A public-facing individual
- A high-profile executive
- A customer of Substack
- Or concerned about credential reuse
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