CVE-2021-21355
No exploitation reported by the sources we read.
- Published2021-03-23
- Fixed in11.1.1 · 10.4.14 · 9.5.25 · 8.7.40
- WeaknessCWE-434 · CWE-552
Am I affected?
Debian, Ubuntu or Red Hat sometimes backport a fix without changing the upstream version number: such a version reads « to verify », never « affected ».With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.
Description
TYPO3 is an open source PHP based web content management system. In TYPO3 before versions 8.7.40, 9.5.25, 10.4.14, 11.1.1, 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_. Besides that, _UploadedFileReferenceConverter_ transforming uploaded files into proper FileReference domain model objects handles possible file uploads for other extensions as well - given those extensions use the Extbase MVC framework, make use of FileReference items in their direct or inherited domain model definitions and did not implement their own type converter. In case this scenario applies, _UploadedFileReferenceConverter_ accepts any file mime-type and persists files in 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. This is fixed in versions 8.7.40, 9.5.25, 10.4.14, 11.1.1.
Timeline
dates in UTC- 2021-03-2302:15CVE publishedNVD
Observed activity
isMalicious corpus · updated 2026-10-23 18:48 UTCBlock these indicators
- Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-21355?format=txt
- CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-21355?format=csv
- TAXII collection of exploited CVEs
- The EDL and CSV take an API key on the Pro plan.
Versions per branch
NVD| Branch | Affected | Fixed in | Source |
|---|---|---|---|
| 11.x | ≥ 11.0.0, < 11.1.1 | 11.1.1 | NVD |
| 10.x | ≥ 10.0.0, < 10.4.14 | 10.4.14 | NVD |
| 9.x | ≥ 9.0.0, < 9.5.25 | 9.5.25 | NVD |
| 8.x | ≥ 8.0.0, < 8.7.40 | 8.7.40 | NVD |
as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.
Fix
- Update Typo3 to 11.1.1 · 10.4.14 · 9.5.25 · 8.7.40
Advisories and patches
- packagist.orgRelease Notes
- typo3.orgVendor Advisory
Detection
- Nuclei template
- none so far ProjectDiscovery
- Exploit-DB
- no entry Exploit-DB
- Proof-of-concept repositories
- none listed PoC-in-GitHub
Sources
- CNACVSS 3.18.6read 2026-10-23
- NVDCVSS 3.18.6read 2026-10-23
- NVDCVSS 2.07.5read 2026-10-23
- CNAweakness (CWE)CWE-434, CWE-552read 2026-10-23
- FIRST EPSSEPSS score1.6 %2026-10-22
Technical details
- CVSS v3 Vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L
- Published
- 2021-03-23
- Last Modified
- 2026-06-17
- NVD status
- Modified
Frequently asked questions
What is CVE-2021-21355?
Is CVE-2021-21355 actively exploited?
What is the CVSS score for CVE-2021-21355?
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Related vulnerabilities
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