Mattermost Security Updates August 13, 2026

What does this MR do and why?

Update Mattermost from version 10.11.20 to 10.11.23 on the 18-11-stable branch. Mattermost 10.11.22 contains high severity security fixes.

This re-creates !9635 (closed) (originally by @heiko.thiel) with the identical change. The original MR was closed by the author due to frustration with the MR process and CI issues, and they invited a maintainer to re-submit it.

The full changelog for this release can be found here.

Related issues

• Supersedes !9635 (closed)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The original MR has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).

Note to the merge request author and maintainer

If you have questions about the patch release process, please:

• Refer to the patch release runbook for engineers and maintainers for guidance.
• Ask questions on the #releases Slack channel (internal only).