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CVE-2021-21370

Cross-Site Scripting (XSS) in typo3/cms-backend (CVE-2021-21370)

Summary

Cross-site scripting in typo3/cms-backend (CVE-2021-21370). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 11.1.1 or later.

Original description

The description as published by the source.

Problem

It has been discovered that content elements of type menu are vulnerable to cross-site scripting when their referenced items get previewed in the page module. A valid backend user account is needed to exploit this vulnerability.

Solution

Update to TYPO3 versions 7.6.51, 8.7.40, 9.5.25, 10.4.14, 11.1.1 that fix the problem described.

Credits

Thanks to TYPO3 contributor Oliver Bartsch who reported and fixed the issue.

References

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-2021-21370 has been found in typo3/cms-backend.
Risk of unauthorized operations or information disclosure.
What to do: upgrade typo3/cms-backend to 11.1.1 or later.
If unsure, ask your IT team or search "typo3/cms-backend CVE-2021-21370" on the vendor's site.

CVE-2021-21370 (typo3/cms-backend) — CWE-79
Attack vector: remote (network-reachable)
Patched: 11.1.1 — 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

Cross-site scripting (XSS) (CWE-79) exists in typo3/cms-backend.

📍 Affected scope

Check the vendor advisory for the affected versions of typo3/cms-backend.

🔥 Severity

Severity: ?. Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 11.1.1.

🛡️ 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 'typo3/cms-backend' . 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 'typo3/cms-backend' . | 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 typo3/cms-backend 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 typo3/cms-backend to 11.1.1

    ステージング環境で 11.1.1 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

Packagist typo3/cms-backend
[{"type":"ECOSYSTEM","events":[{"introduced":"11.0.0"},{"fixed":"11.1.1"}]}]
Packagist typo3/cms-core
[{"type":"ECOSYSTEM","events":[{"introduced":"9.0.0"},{"fixed":"9.5.25"}]}]
Packagist typo3/cms
[{"type":"ECOSYSTEM","events":[{"introduced":"9.0.0"},{"fixed":"9.5.25"}]}]

References

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