CVE-2026-4339 (GCVE-0-2026-4339)

Vulnerability from cvelistv5 – Published: 2026-06-26 14:44 – Updated: 2026-06-26 15:40
VLAI
Title
SSRF via unvalidated attachment URLs in Mattermost Agents plugin MCP server
Summary
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
6.5 (Medium)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
  • CWE-918 - Server-Side Request Forgery (SSRF)
Assigner
References
URL Tags
https://mattermost.com/security-updates vendor-advisory
Impacted products
Vendor Product Version
Mattermost Mattermost Affected: 10.11.0 , ≤ 10.11.18 (semver)
Affected: 11.6.0 , ≤ 11.6.3 (semver)
Affected: 11.5.0 , ≤ 11.5.6 (semver)
Unaffected: 11.7.0
Unaffected: 10.11.19
Unaffected: 11.6.4
Unaffected: 11.5.7
Create a notification for this product.
Credits
s00me00ne
Show details on NVD website
To clipboard 

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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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