CVE-2026-18551CWE-863broken-access-control

CVE-2026-18551

Medium · published October 16, 2026

CVSS v3.1
6.5
EPSS
0%
Percentile
12.1
In the wild
Unconfirmed
What it is

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

The record
Technical detail
CVSS v3.1
6.5 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N
CVSS v4.0
Not supplied
EPSS
0.00222 · 12.1th percentile
Weakness
CWE-863 · Incorrect Authorization
Published
2026-10-16T11:17Z
References (1)
https://mattermost.com/security-updates · [email protected]
EPSS history
Timeline
  • 17 OCT 03:28Z
    EPSS moved — → 0%
    epss
  • 16 OCT 06:56Z
    Mattermost guest account privilege escalation via member roles API
    cvelistv5
  • 16 OCT 06:56Z
    Mattermost guest account privilege escalation via member roles API
    cvelistv5