6.1

CVSS Score

3.1

-

CVSS Score

Basic Information

Concerned about an active attack path?

Talk to our security experts and see Miggo in action.

Miggo Vulnerability Database

→

CVE-2026-28350

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

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.

(GitHub Advisory)

Miggo Vulnerability Database

→

CVE-2026-28350

CVE-2026-28350:

6.1

CVSS Score

3.1

-

CVSS Score

Basic Information

Is this CVE running in your environment?

Easily map the attack path and prioritize which CVEs are a threat to your organization

Validate Exposure

Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
lxml-html-clean	pip	<= 0.4.3	0.4.4

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability lies in the lxml-html-clean library's default HTML cleaning process, which fails to remove the <base> HTML tag. The analysis of the patch in commit 9c5612ca33b941eec4178abf8a5294b103403f34 pinpoints the exact location of the fix.

The file lxml_html_clean/clean.py contains the Cleaner class, which is responsible for the sanitization logic. The __call__ method of this class iterates through the HTML document and removes unwanted tags.

Before the patch, the __call__ method had no specific logic to handle the <base> tag. The default settings are to remove page structure tags like <head>, but <base> was not included in this set. An attacker could inject a <base href="http://evil.com/"> tag, and it would be preserved in the cleaned output. This would cause all relative links, scripts, and stylesheets on the page to be loaded from the attacker's domain, leading to phishing, XSS, or defacement.

The patch introduces a check within the Cleaner.__call__ method. It adds the <base> tag to the kill_tags set whenever the <head> tag is being removed. This ensures that if the page structure is being cleaned (which is the default behavior), any malicious <base> tags are also eliminated.

Therefore, the vulnerable function is Cleaner.__call__, as it is the method that contains the flawed sanitization logic that allows the <base> tag to pass through. The user-facing function clean_html is the entry point that uses this vulnerable method with its default, insecure configuration.

Vulnerable functions

Cleaner.__call__

lxml_html_clean/clean.py

The `__call__` method of the `Cleaner` class is responsible for sanitizing HTML. Prior to the patch, this method did not have any logic to handle the `<base>` tag. The default configuration of the `Cleaner` class, which is used by the `clean_html` function, removes `<html>`, `<head>`, and `<title>` tags but did not remove `<base>`. This allowed an attacker to inject a `<base>` tag, which would not be removed, leading to the hijacking of all relative URLs on the page. The patch fixes this by explicitly adding the `<base>` tag to the list of tags to be killed if the `<head>` tag is also being removed.

Vulnerability Intelligence
Miggo AI

Unlock WAF rules for this CVE

Generate vendor-ready rules for the observed attack patterns, plus reasoning and safe deployment guidance

Get WAF rules

WAF Protection Rules

WAF Rule

W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.

Reasoning

*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.