Is CVE-2026-19603 being exploited?

No public exploit is currently tracked.

How severe is CVE-2026-19603?

CVE-2026-19603 has a CVSS v3 severity of MEDIUM (4.3).

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CVE-2026-19603

Description

Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to sanitize the active channel field returned by the user status API endpoints, which allows an authenticated user to learn the channel ID of a private channel another user is actively viewing via the status endpoints, without being a member of that channel. Mattermost Advisory ID: MMSA-2026-00765