Writing secure code in Python

Slides for the talk "Writing secure code in Python" presented in EuroPython 2022.

Transcript

1. Writing secure code in Python @yyyyyyyan_ Yan Orestes Software engineer EuroPython
2. “Programming in Python is easy”
3. Is programming in Python easy?
4. 01. eval() is really dangerous
5. eval(expression[, globals[, locals]]) Evaluates a Python expression and return the result. Optional parameters: globals: dict locals: Any mapping object
6. The danger begins when… ⚠
7. What if we clean the global variables?
8. Python automatically inserts builtins… ⚠
9. What if we specifically clean the builtins?
10. Creating a payload
11. Creating a payload ⚠
12. eval() is really dangerous ❤ @SamuelAntilla / netsec.expert ⚠
13. Alternatives - ast.literal_eval(node_or_string) - String parsing
14. So when should we use eval()? When there is no other viable way to accomplish a task
15. So when should we use eval()? When there is no other viable way to accomplish a task (never)
16. 02. arbitrary code execution with pickle
17. Serializes a Python object to a sequence of bytes. Optional parameters: protocol: int denoting the protocol used for the serialization. Currently goes from 0 (oldest) to 5 (Python 3.8) pickle.dump(obj, file, protocol=None, *) pickle.dumps(obj, protocol=None, *)
18. The magic method __reduce__() Used to customize how class instances are serialized. Should return a str or a tuple containing a callable and its parameters.
19. The magic method __reduce__() Used to customize how class instances are serialized. Should return a str or a tuple containing a callable and its parameters. ⚠
20. Opening the pickle jar with pickletools
21. But what about arbitrary code execution?
22. Serializing arbitrary code with marshal
23. And to run it? ⚠
24. Assembling the malicious pickle
25. Demo
26. Prevention pickle signing with HMAC Alternative Using a safer serialization format (JSON)
27. 03. the power of pip install
28. What happens when we run pip install? 1. Identification of base requirements and given parameters 2. Resolution of dependencies and determination of what will be installed 3. Determination of installation method 4. Installation of packages
29. Determination of installation method If wheel is available: Download wheel and install from it; Else: Download package source code; If it's possible to build wheel from source code: Build wheel and install from it; Else: Install from setup.py;
30. setup.py - dynamic metadata
31. Arbitrary code execution in package installation
32. Demo
33. Real life risk Typosquatting
34. Real life risk --extra-index-url https://medium.com/@alex.birsan/dependency-confusion-4a5d60fec610
35. Prevention - --only-binary - --require-hashes - NEVER download a package as sudo/admin
36. Prevention - --only-binary - --require-hashes - NEVER download a package as sudo/admin
37. 04. outdated dependencies
38. Vulnerabilities are found all the time!
39. Prevention - Keep up with the releases of packages we use - Keep up with the CVE vulnerabilities list (cve.mitre.org)
40. 05. outdated python
41. Vulnerabilities are found all the time!
42. Understanding Python's versions status
43. Be cautious with deprecated functions!
44. 06. the problem with pseudorandomness
45. How not to generate secure passwords
46. The random module and the infamous seed
47. Alternatives - The secrets module - os.urandom() - random.SystemRandom
48. 07. watch out for bomb files
49. Billion laughs attack
50. Prevention
51. Tarbombs and path traversal
52. Prevention Don't use extractall() without prior inspection of the files!
53. 08. assert is for debug!
54. What is the purpose of assert?
55. Saving a line with assert?
56. Are not equivalent Are equivalent
57. The __debug__ constant and the -O flag
58. Auditing our code
59. Lots of options! • Codacy (free for open source projects) • Horusec (open source) • Pyre/Pysa (open source) • Coverity Scan (exclusive for open source projects) • Bandit (open source)
60. Using bandit
61. key points to never forget
62. 01. never trust user input
63. 02. avoid running Python code as sudo/admin
64. 03. keep your system up-to-date
65. 04. read the docs
66. 04. read the docs
67. 05. use static code analysis tools
68. Thank you! Twitter: @yyyyyyyan_ GitHub: @yyyyyyyan LinkedIn: /in/yyyyyyyan yan@orestes.tech | contact@yyyyyyyan.tech EuroPython