Vulnerability DatabaseCVE-2026-28759
Mend.io Vulnerability Database
The largest open source vulnerability database
What is a Vulnerability ID?
New vulnerability? Tell us about it!
CVE-2026-28759
Published:May 18, 2026
Updated:June 11, 2026
Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate that a remote cluster has access to a channel before processing membership removal requests during shared channel membership sync, which allows a malicious remote cluster to remove any user from any channel, including private channels, via crafted membership sync messages targeting channels the remote cluster is not authorized to access. Mattermost Advisory ID: MMSA-2026-00576
Affected Packages
https://github.com/mattermost/mattermost.git (GITHUB):
Affected version(s) >=v10.11.0 <v10.11.14
Fix Suggestion:
Update to version v10.11.14
https://github.com/mattermost/mattermost.git (GITHUB):
Affected version(s) >=v11.5.0 <v11.5.2
Fix Suggestion:
Update to version v11.5.2
https://github.com/mattermost/mattermost.git (GITHUB):
Affected version(s) >=v11.4.0 <v11.4.4
Fix Suggestion:
Update to version v11.4.4
github.com/mattermost/mattermost/server/v8 (GO):
Affected version(s) >=v8.0.0-20230429093631-aac4f2337933 <v8.0.0-20260216150504-8738f8c4b3d4
Fix Suggestion:
Update to version v8.0.0-20260216150504-8738f8c4b3d4
github.com/mattermost/mattermost (GO):
Affected version(s) >=v11.5.0 <v11.5.2
Fix Suggestion:
Update to version v11.5.2
github.com/mattermost/mattermost (GO):
Affected version(s) >=v10.11.0 <v10.11.14
Fix Suggestion:
Update to version v10.11.14
github.com/mattermost/mattermost (GO):
Affected version(s) >=v11.4.0 <v11.4.4
Fix Suggestion:
Update to version v11.4.4
Related Resources (4)
https://github.com/mattermost/mattermost/commit/8738f8c4b3d42b2b687a6231e72f313357a2e891
https://nvd.nist.gov/vuln/detail/CVE-2026-28759
https://github.com/mattermost/mattermost
https://mattermost.com/security-updates
Do you need more information?
Contact Us
CVSS v4
Base Score:
5.3
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
LOW
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
LOW
Vulnerable System Availability
NONE
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
4.3
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
LOW
Availability
NONE
Weakness Type (CWE)
Incorrect Authorization
CWE-863
EPSS
Base Score:
0.03