CVE-2026-18551
Mattermost guest account privilege escalation via member roles API
CVSS Score
6.5
EPSS Score
0.0%
EPSS Percentile
0th
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to validate the combination of guest and admin scheme roles which allows an authenticated attacker to escalate a guest account to team or channel admin via a crafted PUT request to the member roles API endpoint.. Mattermost Advisory ID: MMSA-2026-00752
| CWE | CWE-863 |
| Vendor | mattermost |
| Product | mattermost |
| Published | Oct 16, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N Attack Vector
Network
Attack Complexity
Low
Privileges Required
High
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None
Affected Versions
Mattermost / Mattermost
11.10.0 ≤ 11.10.0 11.7.0 ≤ 11.7.9 11.9.0 ≤ 11.9.1 11.8.0 ≤ 11.8.5
Credits
0x7oda7123