Detections
Analytics

Mattermost Server 11.7.x < 11.7.11 / 11.8.x < 11.8.6 / 11.9.x < 11.9.2 / 11.10.x < 11.10.2 Multiple Vulnerabilities (MMSA-2026-00771, MMSA-2026-00775, MMSA-2026-00776)

medium Nessus Plugin ID 350090

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-2026-00771, MMSA-2026-00775, MMSA-2026-00776 advisories.

 - Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to enforce a request body size limit during CSRF validation of plugin requests which allows an authenticated user to exhaust server memory and cause a denial of service via a large request body sent to a plugin endpoint. Mattermost Advisory ID: MMSA-2026-00775. (CVE-2026-96260)

 - Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to apply the internal-connection filter to OAuth endpoint requests, which allows a System Administrator to make the server issue requests to internal network addresses and read the responses via the configured OAuth token and userinfo endpoints. Mattermost Advisory ID: MMSA-2026-00776. (CVE-2026-96259)

 - Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to limit the length of the post ID array accepted by the bulk reactions endpoint which allows an authenticated user to cause excessive database load via a crafted request to POST /api/v4/posts/ids/reactions. Mattermost Advisory ID: MMSA-2026-00771. (CVE-2026-95666)

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 11.7.11, 11.8.6, 11.9.2, 11.10.2, 11.11.0 or later.

See Also

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

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

Plugin Details

Severity: Medium

ID: 350090

File Name: mattermost_server_MMSA-2026-00771_00775_00776.nasl

Version: 1.1

Type: Remote

Family: CGI abuses

Published: 9/25/2026

Updated: 9/25/2026

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: Low

Score: 3

Percentile: 23.61

CVSS v2

Risk Factor: Medium

Base Score: 6.8

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

CVSS Score Source: CVE-2026-96260

CVSS v3

Risk Factor: Medium

Base Score: 6.5

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

Vulnerability Information

CPE: cpe:/a:mattermost:mattermost_server

Required KB Items: installed_sw/Mattermost Server

Patch Publication Date: 9/22/2026

Vulnerability Publication Date: 9/22/2026

Reference Information

CVE: CVE-2026-95666, CVE-2026-96259, CVE-2026-96260

IAVA: 2026-A-1047