CVE-2026-19603 PUBLISHED

Private channel ID disclosure via user status endpoints

Assigner: Mattermost
Reserved: 12.08.2026 Published: 16.10.2026 Updated: 16.10.2026

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

Metrics

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
CVSS Score: 4.3

Product Status

Vendor Mattermost
Product Mattermost
Versions Default: unaffected
  • affected from 11.9.0 to 11.9.1 (incl.)
  • affected from 11.8.0 to 11.8.5 (incl.)
  • affected from 11.7.0 to 11.7.10 (incl.)
  • affected from 11.10.0 to 11.10.1 (incl.)
  • Version 11.11.0 is unaffected
  • Version 11.9.2 is unaffected
  • Version 11.8.6 is unaffected
  • Version 11.7.11 is unaffected
  • Version 11.10.2 is unaffected

Solutions

Update Mattermost to versions 11.11.0, 11.9.2, 11.8.6, 11.7.11, 11.10.2 or higher.

Credits

  • CERT PL finder

References

Problem Types

  • CWE-201: Insertion of Sensitive Information Into Sent Data CWE