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CVE-2026-4339
6.5 MEDIUM
- CVSS version (CVSS): 3.1
- Attack Vector (AV): Local (L)
- Attack Complexity (AC): Low (L)
- Privileges Required (PR): Low (L)
- User Interaction (UI): None (N)
- Scope (S): Changed (C)
- Confidentiality (C): High (H)
- Integrity (I): None (N)
- Availability (A): None (N)
- Modified Attack Vector (MAV): Local (L)
- Modified Attack Complexity (MAC): Low (L)
- Modified Privileges Required (MPR): Low (L)
- Modified User Interaction (MUI): None (N)
- Modified Confidentiality (MC): High (H)
- Modified Scope (MS): Changed (C)
- Modified Integrity (MI): None (N)
- Modified Availability (MA): None (N)
Activity log
- Created suggestion
SSRF via unvalidated attachment URLs in Mattermost Agents plugin MCP server
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
References
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MMSA-2026-00635 vendor-advisory
Affected products
Mattermost
- ==11.5.7
- ==11.7.0
- =<10.11.18
- ==10.11.19
- =<11.5.6
- =<11.6.3
- ==11.6.4
Matching in nixpkgs
pkgs.mattermost
Open source platform for secure collaboration across the entire software development lifecycle
pkgs.mattermostLatest
Open source platform for secure collaboration across the entire software development lifecycle
pkgs.mattermost-desktop
Mattermost Desktop client
pkgs.python312Packages.mattermostdriver
None
pkgs.python313Packages.mattermostdriver
Python Mattermost Driver
Package maintainers
-
@mgdelacroix Miguel de la Cruz <mgdelacroix@gmail.com>
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@numinit Morgan Jones <me+nixpkgs@numin.it>
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@ryantm Ryan Mulligan <ryan@ryantm.com>
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@liff Olli Helenius <liff@iki.fi>
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@jokogr Ioannis Koutras <ioannis.koutras@gmail.com>
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@yayayayaka Yaya <github@uwu.is>