GHSA-6cr4-ccf3-x7h4

### Summary

Missing path validation in `confluence_upload_attachment` allows any authenticated MCP client to read arbitrary files from the server filesystem and exfiltrate their contents to Confluence. On Linux deployments, `/proc/self/environ` yields all runtime secrets in a single call.

--- ### Details

`AttachmentsMixin.upload_attachment()` in `src/mcp_atlassian/confluence/attachments.py` opens the caller-supplied `file_path` with no boundary check:

```python # line 477 files = {"file": (filename, open(file_path, "rb"))} ``` The download path was correctly hardened in GHSA-xjgw-4wvw-rgm4 via `validate_safe_path()` (lines 223, 272). That fix was not applied to the upload path, leaving it completely unguarded. The MCP tool layer (`servers/confluence.py:1295`) passes `file_path` verbatim with no additional sanitization.

--- ### PoC

```bash # 1. Prepare target file (macOS demo; on Linux use /proc/self/environ directly) cp ~/.aws/credentials /tmp/diagram.png

# 2. Call the MCP tool confluence_upload_attachment( content_id = "<any page attacker can edit>", file_path = "/tmp/diagram.png" )

# 3. Download attachment from Confluence — contains raw credentials ``` Tested on mcp-atlassian 0.21.1 against live Confluence Cloud. Attachment confirmed uploaded and retrieved with full credential content intact.

--- ### Impact Any MCP client with edit access to one Confluence page can read arbitrary files from the server process. On shared/Docker deployments, `/proc/self/environ` exposes all users' API tokens in a single request. Exfiltrated Atlassian tokens provide persistent API access independent of MCP, surviving server shutdown or patching.

Incomplete fix of GHSA-xjgw-4wvw-rgm4 — arbitrary file read on upload mirrors the arbitrary file write on download fixed in that advisory.

--- ### Suggested Fix

```python # src/mcp_atlassian/confluence/attachments.py — upload_attachment() # Add after abspath conversion, before open():

try: validate_safe_path(file_path) except ValueError as e: return {"success": False, "error": str(e)} ```

Same fix required in `upload_attachments()` and `src/mcp_atlassian/jira/attachments.py`.