CVE-2026-28759

MEDIUM EPSS 4.8%
Published May 18, 20261mo ago · Modified Jun 17, 20262w ago
4.3 CVSS 3.1
Medium
Find Similar
Published May 18, 2026 1mo ago
Last Modified Jun 17, 2026 2w ago

Description

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

CVSS Details

Base Score
4.3
Exploitability
2.8
Impact
1.4
Vector string
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
Attack Vector Network
Attack Complexity Low
Privileges Required Low
User Interaction None
Scope Unchanged
Confidentiality None
Integrity Low
Availability None

Threat Intelligence

EPSS Exploit Probability
4.8% percentile
Exploit & Patch Status
No Known Exploit
No Patch Available

Weaknesses 1

CWE-863 Incorrect Authorization Authorization

Affected Products 3

VendorProductVersionRange
mattermostmattermost_server*≥10.11.0  –  <10.11.14
mattermostmattermost_server*≥11.4.0  –  <11.4.4
mattermostmattermost_server*≥11.5.0  –  <11.5.2

References 1

  • mattermost.com https://mattermost.com/security-updates
    Vendor Advisory

Remediation

No remediation data recorded yet

Check vendor advisories and the NVD entry for patch availability.