CVE-2026-28735

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate the OAuth token scope on the callback which allows an authenticated Mattermost user to gain access to private repositories via modifying the scope parameter in the GitHub authorization URL.. Mattermost Advisory ID: MMSA-2026-00628

Score

CVSS 3.1 5.4 Medium

Status

Analyzed - responsibledisclosure@mattermost.com

Published

2026-05-22

Last modified

2026-05-22

Weaknesses

CWE-863

Affected products

• Mattermost (Mattermost)
• Mattermost Server (Mattermost)

References

• https://mattermost.com/security-updates