CVE-2026-28735
Medium
Description
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
SeverityMedium
CVSS5.4
Exploit probability—
Product
Mattermost Server
PublishedMay 22, 2026
First seenMay 22, 2026
Weakness typeCWE-863Incorrect authorization
How to fix
Update
- mattermost mattermost_server10.11.15, 11.4.5, 11.5.4, 11.6.1 or later
- github.com/mattermost/mattermost-server11.6.1, 11.5.4, 11.4.5, 10.11.15, 10.11.15+incompatible, 11.4.5+incompatible, 11.5.4+incompatible, 11.6.1+incompatible or later
- github.com/mattermost/mattermost-plugin-github1.0.1-0.20260318132218-6e6b740c4852 or later
Vendor advisories
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mattermost mattermost_server | 10.11.0 ≤ v < 10.11.15, 11.4.0 ≤ v < 11.4.5, 11.5.0 ≤ v < 11.5.4, 11.6.0 ≤ v < 11.6.1 | 10.11.15, 11.4.5, 11.5.4, 11.6.1 |
| github.com/mattermost/mattermost-serverGo | 11.6.0 ≤ v < 11.6.1, 11.5.0 ≤ v < 11.5.4, 11.4.0 ≤ v < 11.4.5, 10.11.0 ≤ v < 10.11.15, 10.11.0+incompatible ≤ v < 10.11.15+incompatible, 11.4.0+incompatible ≤ v < 11.4.5+incompatible, 11.5.0+incompatible ≤ v < 11.5.4+incompatible, 11.6.0+incompatible ≤ v < 11.6.1+incompatible | 11.6.1, 11.5.4, 11.4.5, 10.11.15, 10.11.15+incompatible, 11.4.5+incompatible, 11.5.4+incompatible, 11.6.1+incompatible |
| github.com/mattermost/mattermost-plugin-githubGo | v < 1.0.1-0.20260318132218-6e6b740c4852 | 1.0.1-0.20260318132218-6e6b740c4852 |
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