CVE-2026-19603

Private channel ID disclosure via user status endpoints

State: Published
Severity: 4.3 Medium
Published: Oct 16, 2026
Updated: Oct 16, 2026
Reserved: Aug 12, 2026

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

Scores

CVSS	Score	Vector	Source
3.1	4.3 Medium	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N	Mattermost

Weaknesses

CWE-201 Insertion of Sensitive Information Into Sent Data

Affected Products

Product	Versions
MattermostMattermost	11.9.0 through 11.9.1Affected 11.8.0 through 11.8.5Affected 11.7.0 through 11.7.10Affected 11.10.0 through 11.10.1Affected 11.11.0Not affected 11.9.2Not affected 11.8.6Not affected 11.7.11Not affected 11.10.2Not affected

References

MMSA-2026-00765vendor-advisory

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