CVE-2026-3112

A flaw was found in Mattermost. This vulnerability allows a system administrator to read arbitrary files on the host system. This is possible due to a failure to properly validate Advanced Logging file target paths, which can be exploited by providing a malicious AdvancedLoggingJSON configuration...

CVE-2026-3108

A flaw was found in Mattermost. This vulnerability in the mmctl command-line interface allows attackers to manipulate administrator terminals. By sending specially crafted messages containing ANSI and Operating System Command OSC escape sequences, an attacker can enable screen manipulation, displ...

Improper Neutralization

Overview Affected versions of this package are vulnerable to Improper Neutralization via the mmctl component. An attacker can execute arbitrary terminal escape sequences by sending specially crafted messages, potentially leading to manipulation of administrator terminals, including screen...

Improper Handling of Highly Compressed Data (Data Amplification)

Overview github.com/mattermost/mattermost/server/channels/app is a private-cloud Slack alternative Affected versions of this package are vulnerable to Improper Handling of Highly Compressed Data Data Amplification in the archive extraction process. An attacker can exhaust server memory by uploadi...

Incorrect Authorization

Overview github.com/mattermost/mattermost/server/channels/app is a private-cloud Slack alternative Affected versions of this package are vulnerable to Incorrect Authorization via the group retrieval endpoint. An attacker can enumerate user IDs outside their allowed visibility scope by sending...

Denial of Service (DoS)

Overview github.com/mattermost/mattermost/server/channels/app is a private-cloud Slack alternative Affected versions of this package are vulnerable to Denial of Service DoS due to insufficient validation of incoming request size in the webhook endpoint. An attacker can disrupt service availabilit...

Mattermost allows attackers to manipulate administrator terminals via crafted messages containing ANSI and OSC escape sequences

Mattermost versions 11.2.x = 11.2.2, 10.11.x = 10.11.10, 11.4.x = 11.4.0, 11.3.x = 11.3.1 fail to sanitize user-controlled post content in the mmctl commands terminal output which allows attackers to manipulate administrator terminals via crafted messages containing ANSI and OSC escape sequences...

Mattermost allows system administrators to read arbitrary host files via malicious AdvancedLoggingJSON configuration

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to validate Advanced Logging file target paths which allows system administrators to read arbitrary host files via malicious AdvancedLoggingJSON configuration in support packet generation. Mattermost...

Mattermost doesn't set permissions on downloaded bulk export

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to set permissions on downloaded bulk export which allows other local users on the server to be able to read contents of the bulk export. Mattermost Advisory ID: MMSA-2026-00593...

EUVD-2026-16246

Mattermost Plugins versions =11.4 11.0.4 11.1.3 11.3.2 10.11.11.0 fail to validate incoming request size which allows an authenticated attacker to cause service disruption via the webhook endpoint. Mattermost Advisory ID: MMSA-2026-00589...

GHSA-3439-VQGJ-2GCF Mattermost allows attackers to manipulate administrator terminals via crafted messages containing ANSI and OSC escape sequences

Mattermost versions 11.2.x = 11.2.2, 10.11.x = 10.11.10, 11.4.x = 11.4.0, 11.3.x = 11.3.1 fail to sanitize user-controlled post content in the mmctl commands terminal output which allows attackers to manipulate administrator terminals via crafted messages containing ANSI and OSC escape sequences...

GHSA-VHGH-G7X8-4RX8 Mattermost doesn't validate decompressed archive entry sizes during file extraction

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to validate decompressed archive entry sizes during file extraction which allows authenticated users with file upload permissions to cause a denial of service via crafted zip archives containing highly...

EUVD-2026-16236

Mattermost Plugins versions =11.4 10.11.11.0 fail to validate webhook request timestamps which allows an attacker to corrupt Zoom meeting state in Mattermost via replayed webhook requests. Mattermost Advisory ID: MMSA-2026-00584...

GHSA-4765-V66X-RQX7 Mattermost doesn't set permissions on downloaded bulk export

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to set permissions on downloaded bulk export which allows other local users on the server to be able to read contents of the bulk export. Mattermost Advisory ID: MMSA-2026-00593...

EUVD-2026-16234

Mattermost versions 11.2.x = 11.2.2, 10.11.x = 10.11.10, 11.4.x = 11.4.0, 11.3.x = 11.3.1 fail to sanitize user-controlled post content in the mmctl commands terminal output which allows attackers to manipulate administrator terminals via crafted messages containing ANSI and OSC escape sequences...

EUVD-2026-16240

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to set permissions on downloaded bulk export which allows other local users on the server to be able to read contents of the bulk export.. Mattermost Advisory ID: MMSA-2026-00593...

EUVD-2026-16238

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to validate Advanced Logging file target paths which allows system administrators to read arbitrary host files via malicious AdvancedLoggingJSON configuration in support packet generation. Mattermost...

EUVD-2026-16242

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to validate decompressed archive entry sizes during file extraction which allows authenticated users with file upload permissions to cause a denial of service via crafted zip archives containing highly...

GHSA-3MW5-466Q-295Q Mattermost allows system administrators to read arbitrary host files via malicious AdvancedLoggingJSON configuration

Mattermost versions 11.4.x = 11.4.0, 11.3.x = 11.3.1, 11.2.x = 11.2.3, 10.11.x = 10.11.11 fail to validate Advanced Logging file target paths which allows system administrators to read arbitrary host files via malicious AdvancedLoggingJSON configuration in support packet generation. Mattermost...

EUVD-2026-16245

Mattermost versions 11.2.x = 11.2.2, 10.11.x = 10.11.10, 11.4.x = 11.4.0, 11.3.x = 11.3.1 fail to apply view restrictions when retrieving group member IDs, which allows authenticated guest users to enumerate user IDs outside their allowed visibility scope via the group retrieval endpoint...