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medium severity October 23, 2025 · 663K affected

Substack Data Breach (2025)

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.

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Severity Medium
Disclosed October 23, 2025
Affected 663K
Data exposed Email addressesPhone numbers
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