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EUVD-2026-39779 · Published Jun 26, 2026
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
Technologies
Mattermost Mattermost Server
Weaknesses
CWE-918
CVSS scores
- v3.16.5
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N
MITRE ATT&CK
InferredWhere this vulnerability fits in an attack
Privilege Escalation
References
Potentially impacted assets
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