Consider switching from lxml's clean_html for enhanced security (and possibly performance)

I'd like to bring to your attention that we are discussing the possibility of removing lxml's clean_html functionality from lxml library. Over the past years, there have been several concerning security vulnerabilities discovered within the lxml library's clean_html functionality – CVE-2021-43818, CVE-2021-28957, CVE-2020-27783, CVE-2018-19787 and CVE-2014-3146.

The main problem is in the design. Because the lxml's clean_html functionality is based on a blocklist, it's hard to keep it up to date with all new possibilities in HTML and JS.

Two viable alternatives worth considering are bleach and nh3. Here's why:

bleach:

Bleach is a widely adopted Python library specifically designed for sanitizing and cleaning HTML input.
It has a strong track record in terms of security – it's allowed-list-based.
It was deprecated in January but it will still receive security updates, support for new Pythons and bugfixes, see upstream issue.

nh3:

nh3 is Python binding for the ammonia library. Ammonia is written in Rust and it's also allowed-list-based.
Thanks to the Rust backend, nh3 is also significantly faster than bleach.
Rust backend is nothing to be afraid of. nh3 uses the latest PyO3 compatible with Python 3.12 and provides wheels built on top of compatible ABI for different architectures and platforms.

We'll probably move the cleaning part of the lxml to a distinct project first so it will still be possible to use it but better is to find a suitable alternative sooner rather than later.

Let me know if we can help you with this transition anyhow and have a nice day.

Just an update on this. The latest version of lxml (5.2.0) no longer contains the HTML cleaner. Its code is now available as a dedicated project on GitHub and PyPI.

If you want to continue using it, you can either depend on lxml[html_clean] or on lxml_html_clean directly. lxml contains backward-compatible import so there is nothing else you need to change than the dependency.

Thanks, we use bleach already and we'll move to bleach then.

Hey! Thanks for this awesome project 🙏

Quick question, I'm trying to use readability and I'm getting this error:

from readability import Document

  File ".../my_file.py", line 3, in <module>
    from readability import Document
  File ".../python3.8/site-packages/readability/__init__.py", line 3, in <module>
    from .readability import Document
  File ".../python3.8/site-packages/readability/readability.py", line 11, in <module>
    from .cleaners import clean_attributes
  File ".../python3.8/site-packages/readability/cleaners.py", line 3, in <module>
    from lxml.html.clean import Cleaner
  File ".../python3.8/site-packages/lxml/html/clean.py", line 18, in <module>
    raise ImportError(
ImportError: lxml.html.clean module is now a separate project lxml_html_clean.
Install lxml[html_clean] or lxml_html_clean directly.

Is this my fault / something I can fix on my end?

Apologies if this is an obvious issue.

@clintgibler

Hi @clintgibler. The fix for this should be implemented in readability project but in the meantime, you can workaround the problem by simply following the advice from the error message: install lxml[html_clean] or lxml_html_clean - those should be equivalent for you. An alternative is to install an older version of lxml (lxml<5.2.0 should work IIRC).

@frenzymadness

Thanks so much for the quick response @frenzymadness 🙏 . Yes, pip install lxml[html_clean] worked.

Add lxml[html-clean] explicitly

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Consider switching from lxml's clean_html for enhanced security (and possibly performance) #179

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Consider switching from lxml's clean_html for enhanced security (and possibly performance) #179

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frenzymadness commented on Apr 2, 2024

buriy commented on Apr 2, 2024

clintgibler commented on Apr 17, 2024

frenzymadness commented on Apr 17, 2024

clintgibler commented on Apr 17, 2024

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