CVE-2026-18551

medium

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

References

https://mattermost.com/security-updates

https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-102806

Details

Source: Mitre, NVD

Published: 2026-10-16

Updated: 2026-10-17

Risk Information

CVSS v2

Base Score: 7.7

Vector: CVSS2#AV:N/AC:L/Au:M/C:C/I:C/A:N

Severity: High

CVSS v3

Base Score: 6.5

Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N

Severity: Medium

EPSS

EPSS: 0.00222