Use Safe Parsers in lxml Parsing Functions

[pixeebot]

This codemod sets the parser parameter in calls to lxml.etree.parse and lxml.etree.fromstring if omitted or set to None (the default value). Unfortunately, the default parser=None means lxml will rely on an unsafe parser, making your code potentially vulnerable to entity expansion attacks and external entity (XXE) attacks.

The changes look as follows:

  import lxml.etree
- lxml.etree.parse("path_to_file")
- lxml.etree.fromstring("xml_str")
+ lxml.etree.parse("path_to_file", parser=lxml.etree.XMLParser(resolve_entities=False))
+ lxml.etree.fromstring("xml_str", parser=lxml.etree.XMLParser(resolve_entities=False))

More reading

• https://lxml.de/apidoc/lxml.etree.html#lxml.etree.XMLParser
• https://owasp.org/www-community/vulnerabilities/XML_External_Entity_(XXE)_Processing
• https://cheatsheetseries.owasp.org/cheatsheets/XML_External_Entity_Prevention_Cheat_Sheet.html

I have additional improvements ready for this repo! If you want to see them, leave the comment:

@pixeebot next

... and I will open a new PR right away!

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Feedback | Community | Docs | Codemod ID: pixee:python/safe-lxml-parsing

[dryrunsecurity]

DryRun Security Summary

The code changes address an XML External Entity (XXE) vulnerability by modifying the XML parser configuration to prevent the resolution of external entities, thereby enhancing the application's security against potential attacks.

Expand for full summary

Summary:

The provided code changes address a potential vulnerability related to XML External Entity (XXE) Injection. The original code was using the etree.XMLParser with load_dtd=True and resolve_entities=True, which can potentially allow the parsing of external entities and lead to XXE vulnerabilities. The updated code now uses the lxml.etree.XMLParser with the resolve_entities=False parameter, which prevents the resolution of external entities during the XML parsing process. This is an important security improvement, as XXE vulnerabilities can allow an attacker to read local files, perform server-side request forgery (SSRF), and potentially even achieve remote code execution on the server.

While this change addresses the XXE vulnerability, the application still has several other security issues, such as SQL injection, command injection, and cross-site scripting (XSS), which should also be addressed to improve the overall security posture of the application.

Files Changed:

• insecure-app/app.py: The code changes in this file include the addition of the lxml.etree module import and the modification of the XML parsing code to use the lxml.etree.XMLParser with the resolve_entities=False parameter. This change addresses the potential XXE vulnerability in the application.

Code Analysis

We ran 9 analyzers against 1 file and 0 analyzers had findings. 9 analyzers had no findings.

View PR in the DryRun Dashboard.

[jit-ci]

❌ Jit has detected 2 important findings in this PR that you should review.
The findings are detailed below as separate comments.
It’s highly recommended that you fix these security issues before merge.

[jit-ci]

Security control: Static Code Analysis Python Semgrep

Potential Xxe Vulnerability With Native Python Xml Libraries

Found use of the native Python XML libraries, which is vulnerable to XML external entity (XXE)
attacks. The Python documentation recommends the 'defusedxml' library instead. Use 'defusedxml'.
See https://github.com/tiran/defusedxml for more information.

Severity: HIGH

Learn more about this issue

---

Jit Bot commands and options (e.g., ignore issue)

You can trigger Jit actions by commenting on this PR review:

• #jit_ignore_fp Ignore and mark this specific single instance of finding as “False Positive”
• #jit_ignore_accept Ignore and mark this specific single instance of finding as “Accept Risk”
• #jit_ignore_type_in_file Ignore any finding of type "Potential XXE vulnerability with native Python XML libraries" in insecure-app/app.py; future occurrences will also be ignored.
• #jit_undo_ignore Undo ignore command

[jit-ci]

Security control: Static Code Analysis Python Semgrep

Potential Xxe Vulnerability With Native Python Xml Libraries

Found use of the native Python XML libraries, which is vulnerable to XML external entity (XXE)
attacks. The Python documentation recommends the 'defusedxml' library instead. Use 'defusedxml'.
See https://github.com/tiran/defusedxml for more information.

Severity: HIGH

Learn more about this issue

---

Jit Bot commands and options (e.g., ignore issue)

You can trigger Jit actions by commenting on this PR review:

• #jit_ignore_fp Ignore and mark this specific single instance of finding as “False Positive”
• #jit_ignore_accept Ignore and mark this specific single instance of finding as “Accept Risk”
• #jit_ignore_type_in_file Ignore any finding of type "Potential XXE vulnerability with native Python XML libraries" in insecure-app/app.py; future occurrences will also be ignored.
• #jit_undo_ignore Undo ignore command