CVE-2026-10085: Ordinary group/direct message member can enable group_constrained and remove all channel participants

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-13 · updated 2026-07-14
Weakness: CWE-862

Description

Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to restrict the group_constrained channel flag to public and private channels that support group synchronization, which allows an ordinary group or direct message member to remove all participants from the conversation via the channel patch API.. Mattermost Advisory ID: MMSA-2026-00688

Affected products

Mattermost: from 10.11.0 before 10.11.20; from 11.6.0 before 11.6.5; from 11.7.0 before 11.7.3 — fixed in 10.11.20, 11.6.5, 11.7.3

How to fix

Upgrade to a fixed version: Mattermost 10.11.20, 11.6.5, 11.7.3. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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