CVE-2026-4339

CVSS Score & Metrics

Base Score

6.5 / 10

Vector String

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

Vulnerability 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

Vulnerability Details

Published Date

June 26, 2026

Last Modified

June 26, 2026

CWE ID

CWE-918

Source

NVD

External References

https://mattermost.com/security-updates

CVSS Score & Metrics

Vulnerability Description

Vulnerability Details

External References

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