Detections
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Mattermost Server 11.7.x < 11.7.7 / 11.8.x < 11.8.4 Incorrect Authorization (MMSA-2026-00718)

medium Nessus Plugin ID 338330

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Synopsis

The remote host is affected by an incorrect authorization vulnerability.

Description

The version of Mattermost Server installed on the remote host is affected by a vulnerability as referenced in the MMSA-2026-00718 advisory.

 - Mattermost versions 11.7.x <= 11.7.6, 11.8.x <= 11.8.3 The access control policy unassign endpoint fails to re-validate that each target channel still belongs to the requesting admin's team, which allows an authenticated team administrator to remove ABAC (attribute-based access control) policy assignments from channels outside their team via the policy unassign API after a channel has been moved to another team. Mattermost Advisory ID: MMSA-2026-00718. (CVE-2026-15754)

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

Solution

Upgrade to Mattermost Server version 11.7.7, 11.8.4, 11.9.0 or later.

See Also

https://mattermost.com/security-updates/

Plugin Details

Severity: Medium

ID: 338330

File Name: mattermost_server_MMSA-2026-00718.nasl

Version: 1.3

Type: Remote

Family: CGI abuses

Published: 8/20/2026

Updated: 8/28/2026

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: Low

Score: 3

Percentile: 23.67

CVSS v2

Risk Factor: Medium

Base Score: 4.6

Temporal Score: 3.4

Vector: CVSS2#AV:N/AC:H/Au:M/C:N/I:C/A:N

CVSS Score Source: CVE-2026-15754

CVSS v3

Risk Factor: Medium

Base Score: 4.2

Temporal Score: 3.7

Vector: CVSS:3.0/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:H/A:N

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

CPE: cpe:/a:mattermost:mattermost_server

Required KB Items: installed_sw/Mattermost Server

Exploit Ease: No known exploits are available

Patch Publication Date: 7/17/2026

Vulnerability Publication Date: 8/17/2026

Reference Information

CVE: CVE-2026-15754

IAVA: 2026-A-0875