CVE-2026-18799
Mattermost Server fails to restrict Slack import account binding, allowing team admins to forge posts as existing users
CVSS Score
4.3
EPSS Score
0.0%
EPSS Percentile
0th
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
| CWE | CWE-862 |
| Vendor | mattermost |
| Product | mattermost |
| Published | Oct 16, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None
Affected Versions
Mattermost / Mattermost
11.10.0 ≤ 11.10.0 11.7.0 ≤ 11.7.9 11.9.0 ≤ 11.9.1 11.8.0 ≤ 11.8.5
Credits
Claude and Ada Logics