All vulnerabilities
CVE-2026-18799

Mattermost Server fails to restrict Slack import account binding, allowing team admins to forge posts as existing users

Mattermost MattermostApplications & CMS
Open in ThreatlineRecord JSON
CVSS
4.3Medium
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.15%Chance of exploitation activity in the next 30 days, higher than 4% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed inNone listedNo source names a fixed version. Check the vendor advisory below
Published16 Oct 2026Updated 16 Oct 2026CVE List

What fixes it

No source in this snapshot names a fixed version. The vendor advisories under References are the place to check.

Description

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

Text from CVE List

Affected versions 9

  • Mattermostaffected: 11.10.0 through 11.10.0CVE List
  • Mattermostaffected: 11.7.0 through 11.7.9CVE List
  • Mattermostaffected: 11.9.0 through 11.9.1CVE List
  • Mattermostaffected: 11.8.0 through 11.8.5CVE List
  • Mattermostunaffected: 11.11.0CVE List
  • Mattermostunaffected: 11.10.1CVE List
  • Mattermostunaffected: 11.7.10CVE List
  • Mattermostunaffected: 11.9.2CVE List
  • Mattermostunaffected: 11.8.6CVE List

References 1