LOWCVSS 3.8EPSS 0.3%

CVE-2026-8823

Mattermost has an Incorrect Authorization issue

Published: 2026-06-22
Modified: 2026-09-22
EPSS percentile: 25%
Aliases: GHSA-xmfh-3ccg-c9fx
Sources: github-advisory

Summary

Mattermost versions 11.7.x <= 11.7.0, 10.11.x <= 10.11.17 fail to validate bot targets when demoting users to guests which allows a lower-privileged administrator to degrade arbitrary bot accounts via the standard demote-user API.. Mattermost Advisory ID: MMSA-2026-00669

Affected packages

Ecosystem	Package	Affected versions	Fixed versions
Go	github.com/mattermost/mattermost-server	—	11.7.1, 10.11.18
Go	github.com/mattermost/mattermost/server/v8	—	8.0.0-20260518160100-9bd77d3fc4d2

Remediation: Upgrade to 11.7.1 or later.

References

https://github.com/advisories/GHSA-xmfh-3ccg-c9fx

Includes data from the GitHub Advisory Database, licensed under CC-BY 4.0.

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EPSS scores provided by the FIRST.org Exploit Prediction Scoring System.