Vulnerability · Published Jun 12, 2026 · Assigned by Mattermost
CVE-2026-6739Mattermost: Delegated admins could patch protected default system roles
Medium 6.7
In plain English
A medium-severity incorrect authorization in Mattermost from Mattermost. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 17% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to require system-level permission when patching protected default system roles, which allows authenticated users with delegated user-management permissions to escalate privileges by altering built-in role permissions via the role patch API.. Mattermost Advisory ID: MMSA-2026-00656
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/mattermost/mattermost-server | 11.6.1 | GHSA-m2w9-h2mm-79qr |
| Go | github.com/mattermost/mattermost-server | 11.5.5 | GHSA-m2w9-h2mm-79qr |
| Go | github.com/mattermost/mattermost-server | 10.11.17 | GHSA-m2w9-h2mm-79qr |
| Go | github.com/mattermost/mattermost-server | 10.11.17+incompatible, 11.5.5+incompatible, 11.6.1+incompatible | GO-2026-6285 |
| Go | github.com/mattermost/mattermost-server/v5 | no fix listed | GO-2026-6285 |
| Go | github.com/mattermost/mattermost-server/v6 | no fix listed | GO-2026-6285 |
| Go | github.com/mattermost/mattermost/server/v8 | 8.0.0-20260501142004-99b73d4c4acf | GO-2026-6285 |
| Go | github.com/mattermost/mattermost/server/v8 | 8.0.0-20260501142004-99b73d4c4acf | GHSA-m2w9-h2mm-79qr |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mattermost | Mattermost | 11.6.0 – through 11.6.111.5.0 – through 11.5.410.11.0 – through 10.11.1510.11.0 – through 10.11.16 |
Weakness: CWE-863 · Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L
References
- MMSA-2026-00656 vendor-advisory