MCP Atlassian: Arbitrary File Read & Exfiltration (Confused Deputy) in JIRA update_issue

QFinch assessment

A critical Confused Deputy (Arbitrary File Read & Exfiltration) vulnerability in the Atlassian MCP server (Python) allows an AI agent to exfiltrate sensitive host files and environment secrets. By providing absolute system paths to the attachments parameter of the updateissue tool, an agent can force the privileged MCP process to read and upload any file it has access to—including its own environment variables and host configuration—directly to a Jira ticket.

Potential impact

Critical Credential Theft: Immediate exposure of the JIRAAPITOKEN and any other secrets injected into the MCP server's environment.    Arbitrary File Access: Total exfiltration of any data the host user running the MCP server can read (SSH keys, databases, local source code).    Privilege Escalation & Lateral Movement: Attackers can move from a restricted AI sandbox to full host-system control by stealing tokens or configuration files.

Technical context

The vulnerability is located in the updateissue tool handler. The attachments parameter accepts a list of file paths that are passed directly to the Jira API's upload method without any sanitization or validation. Specifically, the implementation fails to: 1.  Restrict paths to a safe workspace: It accepts absolute paths starting with /. 2.  Prevent directory traversal: It does not filter for ../ sequences. 3.  Validate ownership: It allows the process to read system-level files (like /proc/self/environ) that the calling agent is normally forbidden from accessing due to sandbox restrictions. Because the MCP server typically runs with higher privileges than the AI agent (holding the JIRAAPITOKEN and having wider filesystem access), it acts as a "Confused Deputy," performing exfiltration on behalf of a restricted agent.