CVE-2026-18551
MEDIUM
CVSS 6.5
Published: 2026-10-16
Modified: 2026-10-17
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Description
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
Quick Facts
| CVE ID | CVE-2026-18551 |
| CVSS Score | 6.5 |
| Vector | CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N |
| Published | 2026-10-16 |
| Exploited | No |
| CISA KEV | No |
| PoC | Not public |