CVE-2026-77271: MCP Atlassian: Incomplete path traversal fix allows intra-CWD module overwrite and RCE (bypass of GHSA-xjgw-4wvw-rgm4)

The path traversal fix introduced in v0.17.0 (GHSA-xjgw-4wvw-rgm4) is incomplete. validate_safe_path() is called without an explicit base_dir, defaulting to os.getcwd(). In standard container deployments the process CWD is the application directory (e.g. /app), so paths within that directory, including the application’s own Python source modules, pass validation without raising an exception. An attacker can overwrite a module file and achieve remote code execution on the next process restart. Versions >= 0.17.0 are not fully patched as stated in the original advisory. Confirmed on v0.21.0 (latest).