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

Severity (CVSS)

Base score6.5
SeverityMedium
VersionCVSS 3.1
VectorCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N
Provided byCNA

Weaknesses

  • CWE-918 — CWE-918: Server-Side Request Forgery (SSRF)

Affected products

VendorProductVersions
MattermostMattermost10.11.0 to <=10.11.18; 11.6.0 to <=11.6.3; 11.5.0 to <=11.5.6; 11.7.0; 10.11.19; 11.6.4; 11.5.7

References

Authoritative sources

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Generated from the official CVE List on 27 Jun 2026 07:02 UTC.