Account Binding Vulnerability in Mattermost by Mattermost
CVE-2026-18799

4.3MEDIUM

Key Information:

Vendor

Mattermost
Status
Mattermost
Vendor
CVE Published:
16 October 2026

What is CVE-2026-18799?

The vulnerability in Mattermost allows a team admin to initiate unauthorized account binding through Slack imports. This occurs when system administrators fail to properly control the import process, resulting in authenticated attackers being able to force-add existing Mattermost users to their teams. By leveraging this flaw, attackers can forge and manipulate posts to appear as though they were made by other users, significantly compromising the integrity and security of user identities within the platform.

Affected Version(s)

Mattermost 11.10.0

Mattermost 11.7.0 <= 11.7.9

Mattermost 11.9.0 <= 11.9.1

References

https://mattermost.com/security-updates
vendor-advisory

CVSS V3.1

Score:
4.3
Severity:
MEDIUM
Confidentiality:
None
Integrity:
Low
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Claude and Ada Logics
.