Medium severity6.5NVD Advisory· Published Jun 26, 2026· Updated Jun 29, 2026
CVE-2026-4339
CVE-2026-4339
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
Affected products
3cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*+ 1 more
- cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*range: >=10.11.0,<10.11.19
- (no CPE)range: <=10.11.18, <=11.6.3, <=11.5.6
- Range: <=10.11.18, <=11.6.3, <=11.5.6
Patches
Vulnerability mechanics
References
1- mattermost.com/security-updatesnvdVendor Advisory
News mentions
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