CVE-2021-21357Network attack vector

Arbitrary file persistence via unchecked form options

Published Mar 23, 2021 · Updated Aug 3, 2024

Broken access control in affected TYPO3 CMS releases allows remote authenticated users to persist files in writable directories. The Form Designer backend accepts arbitrary values for predefined Form Framework options, enabling upload MIME-type changes and attacker-chosen storage paths. Access to the form module is required; the default fileDenyPattern still blocks executable names such as .htaccess and malicious.php, bounding default exposure to nonblocked file types.

CVSS severity8.3
High
EPSS probability1.61%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Broken access control in affected TYPO3 CMS releases allows remote authenticated users to persist files in writable directories. The Form Designer backend accepts arbitrary values for predefined Form Framework options, enabling upload MIME-type changes and attacker-chosen storage paths. Access to the form module is required; the default fileDenyPattern still blocks executable names such as .htaccess and malicious.php, bounding default exposure to nonblocked file types.

The record

CVE
CVE-2021-21357
Published
Mar 23, 2021
Updated
Aug 3, 2024
Vendor
in2code GmbH
Product
TYPO3 CMS
Classifications
CWE-20, CWE-434, CWE-22, T1105
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 23, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 10.0.0, <= 10.4.13
  2. Affected versionversion=>= 11.0.0, <= 11.1.0
  3. Affected versionversion=>= 8.0.0, <= 8.7.39
  4. Affected versionversion=>= 9.0.0, <= 9.5.24

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

in2code GmbH · TYPO3 CMSversion=>= 10.0.0, <= 10.4.13; version=>= 11.0.0, <= 11.1.0; version=>= 8.0.0, <= 8.7.39; version=>= 9.0.0, <= 9.5.24

Published CVSS scores

8.3NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H
6.5NVDAV:N/AC:L/Au:S/C:P/I:P/A:P
7.9TYPO3CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H/E:H/RL:O/RC:C
8.3GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
CWE-434Unrestricted Upload of File with Dangerous Type
CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
T1105Ingress Tool Transfer

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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