CVE-2026-18799CWE-862broken-access-control

CVE-2026-18799

Medium · published October 16, 2026

CVSS v3.1
4.3
EPSS
0%
Percentile
4.0
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 restrict Slack import account binding to system administrator-initiated imports which allows an authenticated attacker with team admin privileges to force-add existing Mattermost users to their team and forge posts attributed to those users' identities via a crafted Slack export containing target users' email addresses.. Mattermost Advisory ID: MMSA-2026-00757

The record
Technical detail
CVSS v3.1
4.3 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
CVSS v4.0
Not supplied
EPSS
0.00152 · 4.0th percentile
Weakness
CWE-862 · Missing Authorization
Published
2026-10-16T12:17Z
References (1)
https://mattermost.com/security-updates · [email protected]
EPSS history
Timeline
  • 17 OCT 03:28Z
    EPSS moved — → 0%
    epss
  • 16 OCT 07:16Z
    Mattermost Server fails to restrict Slack import account binding, allowing team admins to forge posts as existing users
    cvelistv5
  • 16 OCT 07:16Z
    Mattermost Server fails to restrict Slack import account binding, allowing team admins to forge posts as existing users
    cvelistv5