CVE-2026-28350: lxml_html_clean: <base> tag injection through default Cleaner configuration

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-03-05 · updated 2026-06-17
Weakness: CWE-116

Description

lxml_html_clean is a project for HTML cleaning functionalities copied from `lxml.html.clean`. Prior to version 0.4.4, the <base> tag passes through the default Cleaner configuration. While page_structure=True removes html, head, and title tags, there is no specific handling for <base>, allowing an attacker to inject it and hijack relative links on the page. This issue has been patched in version 0.4.4.

Affected products

fedora-python lxml_html_clean: before 0.4.4 — fixed in 0.4.4

How to fix

Upgrade to a fixed version: fedora-python lxml_html_clean 0.4.4. Check the vendor advisory for mitigations.

References

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