CVE-2026-4339

medium

Description

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 (SSRF) and exfiltrate data from internal network services via supplying internal URLs as file attachments in post creation requests.. Mattermost Advisory ID: MMSA-2026-00635

References

https://mattermost.com/security-updates

Details

Source: Mitre, NVD

Published: 2026-06-26

Updated: 2026-06-26

Risk Information

CVSS v2

Base Score: 4.6

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

Severity: Medium

CVSS v3

Base Score: 6.5

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N