Is CVE-2021-21357 actively exploited?

No active exploitation of CVE-2021-21357 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2021-21357 be exploited remotely?

Yes. CVE-2021-21357 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2021-21357?

CVE-2021-21357 has a CVSS score of 8.3 (HIGH).

HOME VULNERABILITIESCVE-2021-21357

HIGH

CVE-2021-21357

CWE-20Published: March 23, 2021· Updated: Jun 17, 2026

8.3

CVSS v3.1

Official 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 improper input validation, attackers can by-pass restrictions of predefined options and submit arbitrary data in the Form Designer backend module of the Form Framework. In the default configuration of the Form Framework this allows attackers to explicitly allow arbitrary mime-types for file uploads - however, default _fileDenyPattern_ successfully blocked files like _.htaccess_ or _malicious.php_. Besides that, attackers can persist those files in any writable directory of the corresponding TYPO3 installation. A valid backend user account with access to the form module is needed to exploit this vulnerability. This is fixed in versions 8.7.40, 9.5.25, 10.4.14, 11.1.1.

NVD Source

Technical Analysis

CVE-2021-21357 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

Exploitation requires low privileges, which limits the exposure to scenarios where an attacker has already gained initial access.

A successful exploit results in full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 8.3.