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CVE-2021-43818

Vulnerability in lxml (CVE-2021-43818)

Summary

Vulnerability in lxml (CVE-2021-43818). Data can be tampered with by attackers. Mitigation: upgrade to 4.6.5 or later.

Original description

The description as published by the source.

Impact

The HTML Cleaner in lxml.html lets certain crafted script content pass through, as well as script content in SVG files embedded using data URIs.

Users that employ the HTML cleaner in a security relevant context should upgrade to lxml 4.6.5.

Patches

The issue has been resolved in lxml 4.6.5.

Workarounds

None.

References

The issues are tracked under the report IDs GHSL-2021-1037 and GHSL-2021-1038.

Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV

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-2021-43818 has been found in lxml.
Data can be tampered with by attackers.
What to do: upgrade lxml to 4.6.5 or later.
If unsure, ask your IT team or search "lxml CVE-2021-43818" on the vendor's site.

CVE-2021-43818 (lxml) — CWE-74
Attack vector: remote (network-reachable) / unauthenticated
Patched: 4.6.5 — 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-74) exists in lxml.

📍 Affected scope

Check the vendor advisory for the affected versions of lxml.

🔥 Severity

Severity: ?. Data can be tampered with by attackers.

🔧 How to fix

Update to 4.6.5.

🛡️ 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' . 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' . | 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 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 to 4.6.5

    ステージング環境で 4.6.5 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

PyPI lxml
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.6.5"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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