Description
Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username.. Mattermost Advisory ID: MMSA-2026-00649
CVSS breakdown
CVSS 3.1
Attack Vector
Network
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None
Affected products
- Mattermost / Mattermost11.6.0 – 11.6.1
- Mattermost / Mattermost11.5.0 – 11.5.4
- Mattermost / Mattermost10.11.0 – 10.11.15
- Mattermost / Mattermost10.11.0 – 10.11.16
- Mattermost / Mattermost11.7.0 – 11.7.0
- Mattermost / Mattermost11.6.2 – 11.6.2
- Mattermost / Mattermost11.5.5 – 11.5.5
- Mattermost / Mattermost10.11.16 – 10.11.16
- Mattermost / Mattermost10.11.17 – 10.11.17