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Substack Data Breach History

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Substack is a platform for writers to publish newsletters and monetize their audiences.

This page shows all data breaches of Substack. View the complete breach timeline, records exposed, root causes, and AI breach risk score. BreachHistory tracks disclosed data breaches worldwide.

2Total breaches
1.4MRecords breached
October 2025Last breach
37 AI Breach Risk score Moderate

Data Breach Timeline — All Substack Breaches

Substack Data Breach Summary

This page tracks the Substack data breach history and cybersecurity incidents affecting Substack. BreachHistory currently indexes 2 publicly disclosed or catalogued incidents spanning 2025 through 2026, with approximately 1.4 million records reported as exposed across all indexed events. These totals may include overlapping datasets or third-party estimates and should not be interpreted as unique affected users.

The Substack breach timeline includes major data breaches, cyber attacks, data leaks, credential exposures, API abuse, and other security incidents. Each incident provides details on the estimated records exposed, attack method, affected data types, and supporting public sources. Currently, 0 incidents are company-confirmed.

Largest Substack Data Breaches

The largest indexed incidents include the 2026 Substack — BreachForums leak, 697,313 records and the 2025 Substack — ~697K records (Oct 2025, discovered Feb 2026). Record counts originating from threat actors or leak sites should be treated as estimates unless confirmed by Substack or a regulator. Below is the list of large data breaches:

What Information Was Exposed?

Depending on the incident, exposed data may include email addresses, phone numbers, names, profile information, and other personal information (PII). The exact data varies between incidents, so review each breach page before assuming your information was affected.

Substack Data Breach 2026

At the time of this update, BreachHistory catalogues 1 2026 incident related to Substack. Most recent entry: 2026 Substack — BreachForums leak, 697,313 records. New incidents are added as official disclosures, regulatory filings, or credible cybersecurity reports become available.

What To Do If You Were Affected

If you believe your account may have been involved in a Substack data breach, change any reused passwords, enable multi-factor authentication (MFA), monitor your account for suspicious activity, and be cautious of phishing emails or fake breach notifications.

This Substack breach history is maintained by BreachHistory using public disclosures, regulatory filings, security research, and clearly labelled third-party claims. For the complete breach timeline, records exposed, incident details, and AI Breach Risk Score, explore the sections on this page.

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