MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to version 0.17.0, the `confluence_download_attachment` MCP tool accepts a `download_path` parameter that is written to without any directory boundary enforcement. An attacker who can call this tool and supply or access a Confluence attachment with malicious content can write arbitrary content to any path the server process has write access to. Because the attacker controls both the write destination and the written content (via an uploaded Confluence attachment), this constitutes for arbitrary code execution (for example, writing a valid cron entry to `/etc/cron.d/` achieves code execution within one scheduler cycle with no server restart required). Version 0.17.0 fixes the issue.
PoC: CVE-2026-27825
Path Traversal in mcp-atlassian via zip extraction in upload_attachment — CVSS 9.3
PoC: MCPwnfluence
Information about CVE-2026-27825 & CVE-2026-27826 discovered by Pluto Security and a bash script for identifying vulnerable mcp-atlassian instances allowing for automatic update to a fixed version.
CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
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