CVE-2026-4339

MediumCVSS 6.5/10Last modified Jun 29, 2026

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

Metrics

CVSS 3.1 6.5/10CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N

Weakness enumeration

CWE-918

Affected software

No affected versions have been published.

Timeline

Published
Jun 26, 2026
Last modified
Jun 29, 2026
NVD status
Analyzed

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CVE-2026-4339: Medium severity, CVSS 6.5 | Vulnix