CVE-2026-4339

SSRF via unvalidated attachment URLs in Mattermost Agents plugin MCP server

CVSS 6.5 MEDIUMEPSS 0.1%CWE-918

Vexday Risk Score

13Baixo

Decisão SSVC (CISA)

Track

Sem sinal de exploração → monitorar

CVSS 6.5EPSS 0.1%KEV nãoPoC —Nuclei —Metasploit —Patch referenciado

Ciclo de vida

26 jun 2026Publicada no NVD

Recomendação: Monitorar — sem sinal de exploração no momento.

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

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

Produtos afetados

Mattermost · Mattermost

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Referências

https://mattermost.com/security-updates