GHSA-3439-vqgj-2gcf Mattermost allows attackers to manipulate administrator terminals via crafted messages containing ANSI and OSC escape sequences

• Go github.com/mattermost/mattermost/server/v8: >= 11.4.0-rc1, < 11.4.1 → fixed in 11.4.1 • Go github.com/mattermost/mattermost/server/v8: >= 11.3.0-rc1, < 11.3.2 → fixed in 11.3.2 • Go github.com/mattermost/mattermost/server/v8: >= 11.2.0-rc1, < 11.2.3 → fixed in 11.2.3 • Go github.com/mattermost/mattermost/server/v8: >= 10.11.0-rc1, < 10.11.11 → fixed in 10.11.11 • Go github.com/mattermost/mattermost/server/v8: >= 8.0.0-20260105080200-d27a2195068d, < 8.0.0-20260217110922-b7d4a1f1f59b → fixed in 8.0.0-20260217110922-b7d4a1f1f59b

Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to sanitize user-controlled post content in the mmctl commands terminal output which allows attackers to manipulate administrator terminals via crafted messages containing ANSI and OSC escape sequences that enable screen manipulation, fake prompts, and clipboard hijacking. Mattermost Advisory ID: MMSA-2026-00599.