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CVE-2026-4339

MEDIUM
6.5
CVSS 3.1
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

Metadata

CVE ID
CVE-2026-4339
State
PUBLISHED
Assigner
Mattermost
Reserved
2026-03-17 14:57 UTC
Published
2026-06-26 14:44 UTC
Last updated
2026-06-26 15:40 UTC
Primary CWE
CWE-918
CWE-918: Server-Side Request Forgery (SSRF)
Vendor / Product
Mattermost / Mattermost
Sources
cve.org  ·  NVD

Severity & Metrics

6.5 MEDIUM CVSS 3.1
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N
SSVC — CISA Coordinator
Exploitation
none
Automatable
no
Tech. Impact
partial
Affected products (1)
VendorProductPlatformVersions
Mattermost Mattermost — 10.11.0 ≤ 10.11.18, 11.6.0 ≤ 11.6.3, 11.5.0 ≤ 11.5.6, 11.7.0 …
Weakness (CWE)
CWESourceDescription
CWE-918 cna CWE-918: Server-Side Request Forgery (SSRF)
CVSS scores (1)
ScoreSeverityVersionSourceVector
6.5 MEDIUM 3.1 cna CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N
References (1)
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