CVE-2024-39777: Mattermost

Critical severity, CVSS 9.6. EPSS: 0.4% chance of exploitation in the next 30 days.

Mattermost versions 9.9.x <= 9.9.0, 9.5.x <= 9.5.6, 9.7.x <= 9.7.5 and 9.8.x <= 9.8.1 fail to disallow unsolicited invites to expose access to local channels, when shared channels are enabled, which allows a malicious remote to send an invite with the ID of an existing local channel, and that local channel will then become shared without the consent of the local admin.

Affected products

• Mattermost Mattermost: from 9.5.0, before 9.5.7 (fixed in 9.5.7); from 9.7.0, before 9.7.6 (fixed in 9.7.6); from 9.8.0, before 9.8.2 (fixed in 9.8.2); version 9.9.0 only

Published 2024-08-01. Last modified 2026-06-17.