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Mattermost doesn't require system-level permission when patching protected default system roles

Moderate severity GitHub Reviewed Published Jun 12, 2026 to the GitHub Advisory Database • Updated Aug 24, 2026

Package

gomod github.com/mattermost/mattermost-server (Go)

Affected versions

= 11.6.0
>= 11.5.0, <= 11.5.4
>= 10.11.0, <= 10.11.15

Patched versions

11.6.1
11.5.5
10.11.17
gomod github.com/mattermost/mattermost/server/v8 (Go)
>= 8.0.0-20250731163400-5b955468ea1e, < 8.0.0-20260501142004-99b73d4c4acf
8.0.0-20260501142004-99b73d4c4acf

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

References

Published by the National Vulnerability Database Jun 12, 2026
Published to the GitHub Advisory Database Jun 12, 2026
Reviewed Aug 24, 2026
Last updated Aug 24, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
High
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
Low

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(17th percentile)

Weaknesses

Incorrect Authorization

The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. Learn more on MITRE.

CVE ID

CVE-2026-6739

GHSA ID

GHSA-m2w9-h2mm-79qr

Source code

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