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CVE-2026-49825 high CVSS 8.2

Vulnerability in lxml_html_clean (CVE-2026-49825)

Summary

Vulnerability in lxml_html_clean (CVE-2026-49825). Confidential information can be exposed externally. Exploitable via lxml_html_clean.Cleaner. Mitigation: upgrade to 0.4.5 or later.

Original description

The description as published by the source.

lxml_html_clean.Cleaner does not strip javascript: URLs from namespaced URL attributes (xlink:href)

Reporter: Guillem Lefait · Date: 2026-05-10
Affected: lxml ≤ 6.1.0 and lxml_html_clean ≤ 0.4.4 (latest stable)
Confirmed against: lxml 6.1.0 + lxml_html_clean 0.4.4 on Python 3.13.5, 3.14.4, and 3.15.0a8 (libxml2 2.14.6 / 2.9.14 — bug is in pure-Python sanitizer logic, independent of the libxml2 backend)
Root-cause class: same as CVE-2021-28957 (formaction missing from link_attrs)

Summary

Cleaner filters URL schemes (javascript:, vbscript:, …) by walking links via rewrite_links(), which delegates to iterlinks(), which only yields attributes named in lxml.html.defs.link_attrs. That allow-list contains no prefixed names (xlink:href) and no srcset. As a result, when Cleaner is configured with safe_attrs_only=False — a documented option for callers that want lenient attribute handling but still expect URL-scheme scrubbing — `` survives sanitization untouched, and any browser that follows the SVG-anchor specification will execute the JavaScript when the rendered link is clicked.

CWE: CWE-79 (XSS), with CWE-184 (Incomplete List of Disallowed Inputs) as the underlying defect class.

Affected components

Package Versions tested File / line
lxml 4.9.x, 5.2.1, 6.1.0 `…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-49825 has been found in lxml_html_clean.
Attackers can target a specific entry point like lxml_html_clean.Cleaner over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 8.2/10.
What to do: upgrade lxml_html_clean to 0.4.5 or later.
If unsure, ask your IT team or search "lxml_html_clean CVE-2026-49825" on the vendor's site.

CVE-2026-49825 (lxml_html_clean) — CWE-184 / CVSS v3 8.2
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: lxml_html_clean.Cleaner / lxml / lxml_html_clean / formaction
Patched: 0.4.5 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-184) exists in lxml_html_clean. Attackers reach the vulnerable code path via lxml_html_clean.Cleaner without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of lxml_html_clean. Attack surface: lxml_html_clean.Cleaner / lxml / lxml_html_clean / formaction.

🔥 Severity

Severity: High (CVSS 8.2/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 0.4.5.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'lxml_html_clean' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'lxml_html_clean' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で lxml_html_clean を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade lxml_html_clean to 0.4.5

    ステージング環境で 0.4.5 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

pip lxml_html_clean
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.4.5"}]}]
PyPI lxml-html-clean
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.4.5"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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