CVE-2026-28735
GitHub OAuth Scope Validation
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
INFO
Published Date :
May 22, 2026, 4:26 p.m.
Last Modified :
May 22, 2026, 4:26 p.m.
Remotely Exploit :
Yes !
Source :
Mattermost
Affected Products
The following products are affected by CVE-2026-28735
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | 9302f53e-dde5-4bf3-b2f2-a83f91ac0eee | ||||
| CVSS 3.1 | MEDIUM | MITRE-CVE |
Solution
- Update Mattermost to a fixed version.
- Verify OAuth token scope validation is active.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-28735 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-28735 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
May. 22, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* versions from (including) 10.11.0 up to (excluding) 10.11.15 *cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* versions from (including) 11.4.0 up to (excluding) 11.4.5 *cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* versions from (including) 11.5.0 up to (excluding) 11.5.4 *cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* versions from (including) 11.6.0 up to (excluding) 11.6.1 Added Reference Type Mattermost, Inc.: https://mattermost.com/security-updates Types: Vendor Advisory -
New CVE Received by [email protected]
May. 22, 2026
Action Type Old Value New Value Added 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 Added CVSS V3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N Added CWE CWE-863 Added Reference https://mattermost.com/security-updates