CVE-2026-4339EPSS p1.2%

CVE-2026-4339CVE-2026-4339

mattermost / mattermost_server

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

Scoring

CVSS 6.5 ()
VectorCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N
EPSS0.10% probability of exploitation · percentile 1.2% · 2026-08-11T12:00:17Z
Last modified2026-06-29
Sourced from NVD + FIRST.org EPSS. Curated for EU compliance use cases by Adam Lundqvist, Founder at SQUR.