CVE-2026-77255

### Summary 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 update_issue 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. ### Details The vulnerability is located in the update_issue 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 JIRA_API_TOKEN and having wider filesystem access), it acts as a "Confused Deputy," performing exfiltration on behalf of a restricted agent. ### PoC To reproduce the vulnerability in an environment where the agent is sandboxed (e.g., as a restricted Unix user) but the MCP server has host-level access: 1.  Exfiltrate MCP Secrets:     The agent calls the update_issue tool with the following payload: { "issue_key": "SECURITY-1", "attachments": ["/proc/self/environ"] }     Result: The MCP server reads its own process environment—containing the JIRA_API_TOKEN and other sensitive keys in plain text—and attaches it to the Jira issue. 2.  Exfiltrate Host Configuration:     The agent calls the tool to target global assistant settings: { "issue_key": "SECURITY-1", "attach