VULNERABILITY INTELLIGENCE

CVE-2026-4339

CVSS score6.5 MEDIUM
EPSS probability0.14%
CISA KEVNot currently listed
Published2026-06-26
Last modified2026-06-29
CVSS vectorCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N

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

Weakness classification

  • CWE-918: Server-Side Request Forgery (SSRF)

Primary references