All vulnerabilities
CVE-2026-19603

Mattermost: Private channel ID disclosure via user status endpoints

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)0.18%Chance of exploitation activity in the next 30 days, higher than 6% 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 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to sanitize the active channel field returned by the user status API endpoints, which allows an authenticated user to learn the channel ID of a private channel another user is actively viewing via the status endpoints, without being a member of that channel. Mattermost Advisory ID: MMSA-2026-00765

Text from CVE List

Affected versions 9

  • Mattermostaffected: 11.9.0 through 11.9.1CVE List
  • Mattermostaffected: 11.8.0 through 11.8.5CVE List
  • Mattermostaffected: 11.7.0 through 11.7.10CVE List
  • Mattermostaffected: 11.10.0 through 11.10.1CVE List
  • Mattermostunaffected: 11.11.0CVE List
  • Mattermostunaffected: 11.9.2CVE List
  • Mattermostunaffected: 11.8.6CVE List
  • Mattermostunaffected: 11.7.11CVE List
  • Mattermostunaffected: 11.10.2CVE List

References 1