CVE-2026-20796

LOW3.1EPSS 0.01%

Mattermost doesn't properly validate channel membership at the time of data retrieval

Published: 2/13/2026Modified: 2/23/2026

Also known as:GHSA-2xf7-hmf6-p64jGO-2026-4495

Description

Mattermost versions 10.11.x <= 10.11.9 fail to properly validate channel membership at the time of data retrieval which allows a deactivated user to learn team names they should not have access to via a race condition in the /common_teams API endpoint.. Mattermost Advisory ID: MMSA-2025-00549

Affected packages (2)

Go/github.com/mattermost/mattermost-server>= 10.11.0, < 10.11.10
Go/github.com/mattermost/mattermost-server>= 10.11.0+incompatible, < 10.11.10+incompatible

CVSS scores

Source	Version	Severity	Vector
osv	CVSS 3.1	LOW3.1	CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N

References (4)

ADVISORYhttps://github.com/advisories/GHSA-2xf7-hmf6-p64j
ADVISORYhttps://nvd.nist.gov/vuln/detail/CVE-2026-20796
PATCHhttps://github.com/mattermost/mattermost
WEBhttps://mattermost.com/security-updates