CVE-2026-40300: Zulip Server

Medium severity, CVSS 6.5. EPSS: 0.4% chance of exploitation in the next 30 days.

Zulip is an open-source team collaboration tool. Prior to 12.0, With message_edit_history_visibility_policy set to "moves", /api/v1/messages/{id}/history still returns historical content values, allowing low-privilege users to recover text that was edited away from other users' messages. This vulnerability is fixed in 12.0.

Affected products

• Zulip Zulip Server: version 10.0 only

Published 2026-05-12. Last modified 2026-06-17.