CVE-2026-61536: Banks: Unsafe importlib.import_module of attacker-controlled Tool.import_path in CompletionExtension allows RCE

Banks generates meaningful LLM prompts using a simple template language. In versions prior to 2.4.3, banks parses Tool JSON objects from the rendered body of {% completion %} blocks and later resolves their importpath field through importlib.importmodule(...) + getattr(...) to obtain the callable that handles a tool call. There is no allowlist or sanitization on importpath, so any importable Python attribute (e.g. os.system, subprocess.getoutput) can be selected. When the LLM emits a toolcalls entry whose function.name matches the attacker-supplied tool name, the resolved callable is invoked with kwargs decoded from toolcall.function.arguments, yielding arbitrary code execution in the banks-hosting process. This is distinct from GHSA-gphh-9q3h-jgpp / CVE-2026-44209. That advisory was fixed in 2.4.2 by switching src/banks/env.py from Environment to SandboxedEnvironment. The fix does not touch src/banks/extensions/completion.py, and the unsafe import + getattr chain still executes on 2.4.2. The malicious Tool JSON is plain text in the rendered template body — it requires no Jinja attribute access, so the sandbox is irrelevant. This issue has been fixed in version 2.4.3.