CVE-2026-77268

## Summary The OAuth token fallback file storage in `OAuthConfig._save_tokens_to_file()` creates token files containing access tokens, refresh tokens, and cloud IDs with default filesystem permissions (typically `0644` on Linux, world-readable). Any local user on a shared system can read these files to obtain full Atlassian API credentials, enabling unauthorized access to the victim's Jira and Confluence data. ## Details The vulnerability exists in `src/mcp_atlassian/utils/oauth.py` in the `_save_tokens_to_file` method. **Step 1 -- Directory created without restrictive permissions:** At line 402-403, the token directory is created with `mkdir(exist_ok=True)` which uses the default umask (typically creating directories with mode `0755`): ```python # src/mcp_atlassian/utils/oauth.py:402-403 token_dir = Path.home() / ".mcp-atlassian" token_dir.mkdir(exist_ok=True) ``` **Step 2 -- Token file written with default permissions:** At line 417-418, the token file containing sensitive credentials is written using `open()` with no explicit mode, inheriting default umask permissions (typically `0644` on Linux): ```python # src/mcp_atlassian/utils/oauth.py:406-418 token_path = token_dir / f"oauth-{self.client_id}.json" if token_data is None: token_data = { "refresh_token": self.refresh_token, "access_token": self.access_token, "expires_at": self.expires_at, "cloud_id": self.cloud_id, "base_url": self.base_url, } with open(token_path, "w") as f: json.dump(token_data, f) ``` **Step 3 -- The file contains full API credentials:** The token file contains: - `access_token`: A valid OAuth access token for the Atlassian API - `refresh_token`: Can be exchanged for new access tokens indefinitely - `cloud_id`: Identifies the target Atlassian Cloud instance - `base_url`: The target Data Center instance URL **No `os.chmod` or `os.fchmod` is called** anywhere after file creation. The primary storage via `keyring` (line 373) is