Unrestricted File Upload in typo3/cms-form (CVE-2021-21355)
Summary
Vulnerability in typo3/cms-form (CVE-2021-21355). Data can be tampered with by attackers. Mitigation: upgrade to 11.1.1 or later.
Original description
The description as published by the source.
Problem
Due to the lack of ensuring file extensions belong to configured allowed mime-types, attackers can upload arbitrary data with arbitrary file extensions - however, default fileDenyPattern successfully blocked files like .htaccess or malicious.php.
TYPO3 Extbase extensions, which implement a file upload and do not implement a custom TypeConverter to transform uploaded files into FileReference domain model objects are affected by the vulnerability as well, since the UploadedFileReferenceConverter of ext:form handles the file upload and will accept files of any mime-type which are persisted to the default location.
In any way, uploaded files are placed in the default location /fileadmin/user_upload/, in most scenarios keeping the submitted filename - which allows attackers to directly reference files, or even correctly guess filenames used by other individuals, disclosing this information.
No authentication is required to exploit this vulnerability.
Solution
Update to TYPO3 versions 8.7.40, 9.5.25, 10.4.14, 11.1.1 that fix the problem described.
Type converter UploadedFileReferenceConverter is not registered globally anymore and just handles uploaded files within the scope of the Form Framework. Guessable storage location has changed from /fileadmin/user_upload/form_/ to /fileadmin/form_uploads/. Allowed mime-types must match expected file extensions (e.g. application/pdf must be .pdf, and cannot be .html).
Extbase extensions, w…
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-2021-21355 has been found in typo3/cms-form.
Data can be tampered with by attackers.
What to do: upgrade typo3/cms-form to 11.1.1 or later.
If unsure, ask your IT team or search "typo3/cms-form CVE-2021-21355" on the vendor's site.
CVE-2021-21355 (typo3/cms-form) — CWE-434
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
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.
A vulnerability (CWE-434) exists in typo3/cms-form.
Check the vendor advisory for the affected versions of typo3/cms-form.
Severity: ?. Data can be tampered with by attackers.
Update to 11.1.1.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'typo3/cms-form' . 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
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1Identify exposure identify
grep -r 'typo3/cms-form' . | 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-formを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade typo3/cms-form 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。
-
3Post-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
References
- advisory nvd.nist.gov
- web github.com
- web github.com
- web github.com
- web packagist.org
- web typo3.org