CVE-2026-18799 — Mattermost Server fails to restrict Slack import account binding, allowing team admins to forge posts as existing users
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 impo…
Published: 2026-10-16 · CVSS: 4.3 · CVSS 3.1
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
Source: CVE Program · Revision 8b16575c39f1e1810c5e863010da073d2d3285e7