Detections
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Mattermost Desktop < 5.13.5 / < 6.0.2 / < 6.1.1 Multiple Vulnerabilities (MMSA-2026-00618 / MMSA-2026-00633)

medium Nessus Plugin ID 317394

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Synopsis

The remote host is missing a security update.

Description

The version of Mattermost Desktop installed on the remote host is affected by multiple vulnerabilities as referenced in the MMSA-2026-00618 and MMSA-2026-00633 advisories.

 - Mattermost Desktop App fails to prevent an invalid URL from loading in a pop-up window which allows a malicious server owner to repeatedly crash the application via calling {{window.open('javascript:alert()');
 }}. Mattermost Advisory ID: MMSA-2026-00618. (CVE-2026-3471)

 - Mattermost Desktop App fails to prevent server-rendered content from closing an underlying application view which allows a malicious server or plugin to crash the desktop client via invoking {{window.close()}} in the renderer context, leading to a denial of service condition at the client level. Mattermost Advisory ID: MMSA-2026-00633. (CVE-2026-4643)

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 Desktop version 5.13.5, 6.0.2, 6.1.1, or later.

See Also

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

Plugin Details

Severity: Medium

ID: 317394

File Name: mattermost_desktop_MMSA-2026-00618_MMSA-2026-00633.nasl

Version: 1.3

Type: Local

Agent: windows, macosx, unix

Family: Misc.

Published: 5/28/2026

Updated: 6/1/2026

Configuration: Enable thorough checks (optional)

Supported Sensors: Nessus Agent, Nessus

Risk Information

VPR

Risk Factor: Low

Score: 3.6

CVSS v2

Risk Factor: High

Base Score: 7.8

Temporal Score: 5.8

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

CVSS Score Source: CVE-2026-3471

CVSS v3

Risk Factor: Medium

Base Score: 6.5

Temporal Score: 5.7

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

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

Vulnerability Information

CPE: cpe:/a:mattermost:mattermost_desktop

Exploit Ease: No known exploits are available

Patch Publication Date: 4/8/2026

Vulnerability Publication Date: 4/9/2026

Reference Information

CVE: CVE-2026-3471, CVE-2026-4643

IAVA: 2026-A-0507