CVE-2026-28735: GitHub OAuth Scope Validation

Published May 22, 2026
·
Updated

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

Affected Software

1 affected component
Mattermost Mattermost=11.6.0, >=11.5.0<=11.5.3, >=11.4.0<=11.4.4, >=10.11.0<=10.11.14

Remediation

Information

Update Mattermost to versions 11.7.0, 11.6.1, 11.5.4, 11.4.5, 10.11.15 or higher.

Event History

May 22, 2026
CVE Published
via MITRE·04:26 PM
Data Sourced
via MITRE·04:26 PM
RemedyDescriptionSeverityWeakness
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Frequently Asked Questions

1

What is the severity of CVE-2026-28735?

CVE-2026-28735 has a medium severity score of 5.4.

2

How do I fix CVE-2026-28735?

To fix CVE-2026-28735, update Mattermost to version 11.7.0, 11.6.1, 11.5.4, 11.4.5, 10.11.15 or higher.

3

What systems are affected by CVE-2026-28735?

CVE-2026-28735 affects Mattermost versions 11.6.x up to 11.6.0, 11.5.x up to 11.5.3, 11.4.x up to 11.4.4, and 10.11.x up to 10.11.14.

4

What vulnerability does CVE-2026-28735 address?

CVE-2026-28735 addresses a lack of OAuth token scope validation on GitHub authorization in Mattermost.

5

Can an authenticated user exploit CVE-2026-28735?

Yes, an authenticated user can exploit CVE-2026-28735 to access private repositories by modifying the OAuth scope parameter.

Company

Resources

Contact

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