EUVD-2026-39778

Mattermost Plugins versions =11.6 10.18.11 11.3.6 11.6.5.0 fail to sanitize error responses from the OpenAI API before logging, which allows a user with access to server logs or support packets to obtain a valid or partially reconstructable OpenAI API key via inspection of mattermost.log entries...

EUVD-2026-39775

Mattermost versions 10.11.x = 10.11.18, 11.6.x = 11.6.3, 11.5.x = 11.5.6 fail to properly apply markdown image rendering restrictions to AI bot tool result posts, which allows an authenticated attacker to exfiltrate data to an attacker-controlled server via injecting markdown image syntax into to...

EUVD-2026-39779

Mattermost versions 10.11.x = 10.11.18, 11.6.x = 11.6.3, 11.5.x = 11.5.6 fail to validate attachment URLs against internal or private IP ranges in the Mattermost Agents plugin MCP server which allows an attacker with access to the MCP server in stdio mode to perform server-side request forgery SS...

EUVD-2026-39661

The Mattermost Go module github.com/mattermost/mattermost/server/public versions v0.1.22 fail to validate path parameters when constructing API route paths which allows an attacker to redirect API calls to unintended endpoints via crafted IDs containing path traversal components. Mattermost...

CVE-2026-9699

Mattermost Plugins versions =11.6 10.18.11 11.3.6 11.6.5.0 fail to sanitize error responses from the OpenAI API before logging, which allows a user with access to server logs or support packets to obtain a valid or partially reconstructable OpenAI API key via inspection of mattermost.log entries...

CVE-2026-4339

Mattermost versions 10.11.x = 10.11.18, 11.6.x = 11.6.3, 11.5.x = 11.5.6 fail to validate attachment URLs against internal or private IP ranges in the Mattermost Agents plugin MCP server which allows an attacker with access to the MCP server in stdio mode to perform server-side request forgery SS...

CVE-2026-3472

Mattermost versions 10.11.x = 10.11.18, 11.6.x = 11.6.3, 11.5.x = 11.5.6 fail to properly apply markdown image rendering restrictions to AI bot tool result posts, which allows an authenticated attacker to exfiltrate data to an attacker-controlled server via injecting markdown image syntax into to...

CVE-2026-4339 SSRF via unvalidated attachment URLs in Mattermost Agents plugin MCP server

Mattermost versions 10.11.x = 10.11.18, 11.6.x = 11.6.3, 11.5.x = 11.5.6 fail to validate attachment URLs against internal or private IP ranges in the Mattermost Agents plugin MCP server which allows an attacker with access to the MCP server in stdio mode to perform server-side request forgery SS...

CVE-2026-9699 Mattermost Agents plugin logs unsanitized OpenAI API keys on authentication errors

Mattermost Plugins versions =11.6 10.18.11 11.3.6 11.6.5.0 fail to sanitize error responses from the OpenAI API before logging, which allows a user with access to server logs or support packets to obtain a valid or partially reconstructable OpenAI API key via inspection of mattermost.log entries...

CVE-2026-9699

Mattermost Plugins versions

CVE-2026-3472 Markdown image rendering bypass in AI bot tool result posts in Mattermost

Mattermost versions 10.11.x = 10.11.18, 11.6.x = 11.6.3, 11.5.x = 11.5.6 fail to properly apply markdown image rendering restrictions to AI bot tool result posts, which allows an authenticated attacker to exfiltrate data to an attacker-controlled server via injecting markdown image syntax into to...

CVE-2026-3472

CVE-2026-3472 affects Mattermost where specific versions (10.11.x <= 10.11.18, 11.6.x <= 11.6.3, 11.5.x

CVE-2026-13426

The Mattermost Go module github.com/mattermost/mattermost/server/public versions v0.1.22 fail to validate path parameters when constructing API route paths which allows an attacker to redirect API calls to unintended endpoints via crafted IDs containing path traversal components. Mattermost...

CVE-2026-13426 Client4 fails to validate path parameters

The Mattermost Go module github.com/mattermost/mattermost/server/public versions v0.1.22 fail to validate path parameters when constructing API route paths which allows an attacker to redirect API calls to unintended endpoints via crafted IDs containing path traversal components. Mattermost...

CVE-2026-13426

The Mattermost Go module github.com/mattermost/mattermost/server/public versions

CVE-2026-2299

The Mattermost Google Drive plugin before version 1.1.0 fails to validate channel membership in the file creation endpoint, allowing authenticated users with a connected Google account to share Google Drive files to unauthorized private channels and disclose private channel membership...

CVE-2026-2299

The Mattermost Google Drive plugin before version 1.1.0 fails to validate channel membership in the file creation endpoint, allowing authenticated users with a connected Google account to share Google Drive files to unauthorized private channels and disclose private channel membership...

EUVD-2026-39540

The Mattermost Google Drive plugin before version 1.1.0 fails to validate channel membership in the file creation endpoint, allowing authenticated users with a connected Google account to share Google Drive files to unauthorized private channels and disclose private channel membership...

CVE-2026-2299

CVE-2026-2299 affects the Mattermost Google Drive plugin prior to version 1.1.0. The file creation endpoint does not validate channel membership, allowing authenticated users with a connected Google account to share Google Drive files into unauthorized private channels and disclose private channe...

CVE-2026-2299 Improper Access Control in Mattermost Google Drive Plugin File Creation Endpoint

The Mattermost Google Drive plugin before version 1.1.0 fails to validate channel membership in the file creation endpoint, allowing authenticated users with a connected Google account to share Google Drive files to unauthorized private channels and disclose private channel membership...