CVE-2021-21355Network attack vector

Unauthenticated arbitrary file upload via MIME mismatch

Published Mar 23, 2021 · Updated Aug 3, 2024

Unrestricted file upload in TYPO3 CMS before 8.7.40, 9.5.25, 10.4.14, or 11.1.1 allows remote attackers to store arbitrary data. The Form Framework's UploadedFileReferenceConverter accepts uploads without ensuring that the filename extension matches an allowed MIME type, then persists them under /fileadmin/user_upload/ with predictable names. No authentication is required; the default fileDenyPattern blocks .php and .htaccess, but other uploaded files remain directly retrievable and can expose data.

CVSS severity8.6
High
EPSS probability1.63%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Unrestricted file upload in TYPO3 CMS before 8.7.40, 9.5.25, 10.4.14, or 11.1.1 allows remote attackers to store arbitrary data. The Form Framework's UploadedFileReferenceConverter accepts uploads without ensuring that the filename extension matches an allowed MIME type, then persists them under /fileadmin/user_upload/ with predictable names. No authentication is required; the default fileDenyPattern blocks .php and .htaccess, but other uploaded files remain directly retrievable and can expose data.

The record

CVE
CVE-2021-21355
Published
Mar 23, 2021
Updated
Aug 3, 2024
Vendor
in2code GmbH
Product
TYPO3 CMS
Classifications
CWE-434, CWE-552, T1190
Attack vector
network
Privileges
unauthenticated

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

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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 privilegesunauthenticated

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

8.0TYPO3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L/E:F/RL:O/RC:C
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
8.6GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L

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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-434Unrestricted Upload of File with Dangerous Type
CWE-552Files or Directories Accessible to External Parties
T1190Exploit Public-Facing Application

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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