Detections
Analytics

Mattermost Server 10.11.x < 10.11.20 / 11.6.x < 11.6.5 / 11.7.x < 11.7.3 Multiple Vulnerabilities (MMSA-2026-00658, MMSA-2026-00676, MMSA-2026-00680, MMSA-2026-00683, MMSA-2026-00688, MMSA-2026-00689, MMSA-2026-00690)

medium Nessus Plugin ID 327418

Synopsis

The remote host is affected by multiple vulnerabilities.

Description

The version of Mattermost Server installed on the remote host is affected by multiple vulnerabilities as referenced in the MMSA-2026-00658, MMSA-2026-00676, MMSA-2026-00680, MMSA-2026-00683, MMSA-2026-00688, MMSA-2026-00689, MMSA-2026-00690 advisories.

 - Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to invalidate OAuth refresh tokens upon user account deactivation, which allows a deactivated user or an attacker in possession of a valid refresh token to obtain new functional access tokens via the OAuth refresh token grant endpoint. Mattermost Advisory ID: MMSA-2026-00680. (CVE-2026-9571)

 - Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to validate the length and content of message attachment field values, which allows an authenticated attacker to cause a denial of service for all users in a channel via a post containing a specially crafted payload that triggers catastrophic backtracking in the client-side markdown parser.
 Mattermost Advisory ID: MMSA-2026-00658. (CVE-2026-6850)

 - Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to verify that the channel referenced in an action cookie matches the channel of the target post, which allows an authenticated user without access to a private channel to trigger interactive post actions on posts in that channel via a cookie obtained from any accessible channel.
 Mattermost Advisory ID: MMSA-2026-00690. (CVE-2026-10106)

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

Solution

Upgrade to Mattermost Server version 10.11.20, 11.6.5, 11.7.3 / 11.8.0 or later.

See Also

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

Plugin Details

Severity: Medium

ID: 327418

File Name: mattermost_server_MMSA-2026-00658_00676_00680_00683_00688_00689_00690.nasl

Version: 1.1

Type: Remote

Family: CGI abuses

Published: 7/16/2026

Updated: 7/16/2026

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: Low

Score: 3

Percentile: 23.8

CVSS v2

Risk Factor: Medium

Base Score: 6.8

Vector: CVSS2#AV:N/AC:L/Au:S/C:C/I:N/A:N

CVSS Score Source: CVE-2026-9571

CVSS v3

Risk Factor: Medium

Base Score: 6.5

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

Vulnerability Information

CPE: cpe:/a:mattermost:mattermost_server

Required KB Items: installed_sw/Mattermost Server

Patch Publication Date: 6/12/2026

Vulnerability Publication Date: 6/12/2026

Reference Information

CVE: CVE-2026-10085, CVE-2026-10103, CVE-2026-10106, CVE-2026-6850, CVE-2026-9571, CVE-2026-9708, CVE-2026-9824