lxml-html-clean has tag injection through default Cleaner configuration

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS

• CVE-2026-28350: 0.30% estimated exploitation activity in the next 30 days; percentile 22.30 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The <base tag passes through the default Cleaner configuration. While pagestructure=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. Details The <base tag is not currently in the pagestructure kill set. Even though the specification says <base must be inside <head, browsers accept <base tags outside of the head. If an attacker injects a <base tag, it changes the base URL for all relative URLs on the page (links, images, scripts) to a domain controlled by the attacker. PoC Impact The injection of a <base tag allows an attacker to hijack the resolution of all relative URLs on the page. This results in three critical attack vectors: 1. Phishing & Redirection: Attackers can redirect user navigation (e.g., <a href="/login") and form submissions (e.g., <form action="/auth") to an attacker-controlled domain, effectively stealing credentials or sensitive data without the user…

Published by the source

2 Mar 2026, 19:35 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:36 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-xvp8-3mhv-424c

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-xvp8-3mhv-424c

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# Patch Next advisory brief: CVE-2026-28350

Advisory: lxml-html-clean has tag injection through default Cleaner configuration
IDs: CVE-2026-28350, GHSA-xvp8-3mhv-424c
Record: https://patchnext.com/advisories/cve-2026-28350 (revision 2, source checked 26 Oct 2026, 13:36 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: lxml-html-clean 0.4.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI lxml-html-clean: affected <= 0.4.3; fixed in 0.4.4

## Suggested inspection (read-only)
- `python -m pip show lxml-html-clean`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on lxml-html-clean.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-xvp8-3mhv-424c (OSV record GHSA-xvp8-3mhv-424c lists affected ranges: PyPI lxml-html-clean >=0 <0.4.4 (fixed))
- Verified: https://github.com/advisories/GHSA-xvp8-3mhv-424c (GitHub-reviewed advisory GHSA-xvp8-3mhv-424c lists affected ranges: PyPI lxml-html-clean >=0 <=0.4.3)

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