CVE-2025-59020: TYPO3 CMS Auth Bypass Vulnerability

CVE-2025-59020 Overview

CVE-2025-59020 is an authorization bypass vulnerability in TYPO3 CMS that allows authenticated backend users to circumvent field-level access controls during record creation. By exploiting the defVals parameter, attackers can insert arbitrary data into prohibited exclude fields of database tables for which they already have write permission on a reduced set of fields. This represents a broken access control issue (CWE-863) that undermines the principle of least privilege in TYPO3's backend permission system.

Critical Impact

Authenticated backend users can bypass field-level restrictions to modify protected database fields, potentially leading to privilege escalation, data integrity violations, or unauthorized configuration changes within the TYPO3 CMS environment.

Affected Products

• TYPO3 CMS versions 10.0.0 through 10.4.54
• TYPO3 CMS versions 11.0.0 through 11.5.48
• TYPO3 CMS versions 12.0.0 through 12.4.40
• TYPO3 CMS versions 13.0.0 through 13.4.22
• TYPO3 CMS versions 14.0.0 through 14.0.1

Discovery Timeline

• January 13, 2026 - CVE-2025-59020 published to NVD
• January 13, 2026 - Last updated in NVD database

Technical Details for CVE-2025-59020

Vulnerability Analysis

This vulnerability stems from improper authorization checks (CWE-863) in TYPO3's backend record creation workflow. The defVals parameter, which is used to set default values for new records, fails to properly validate whether the current user has permission to write to specific fields marked as "exclude" fields in the TCA (Table Configuration Array).

In TYPO3's permission model, administrators can restrict backend users from editing certain sensitive fields by marking them as exclude fields and not granting the corresponding permissions. However, the vulnerable code path allows these restrictions to be bypassed during the record creation process by injecting values through the defVals parameter.

The attack requires the user to already have legitimate write access to the target database table for at least a subset of fields. This is not a complete authentication bypass but rather a horizontal privilege escalation within the backend permission framework.

Root Cause

The root cause is insufficient authorization validation in the record creation handler. When processing the defVals parameter during new record creation, the system fails to cross-reference the provided field names against the user's actual field-level permissions. The code accepts default values for exclude fields without verifying that the authenticated user has explicit permission to modify those specific fields, resulting in an authorization bypass condition.

Attack Vector

The attack is conducted over the network by authenticated backend users. An attacker with valid backend credentials and partial write permissions to a database table can craft a malicious request containing the defVals parameter with field-value pairs for restricted exclude fields.

The exploitation flow involves:

1. Identifying a database table where the attacker has partial write access
2. Determining which fields are marked as exclude fields that the attacker cannot normally modify
3. Crafting a record creation request that includes defVals parameters targeting those restricted fields
4. Submitting the request through the TYPO3 backend, bypassing field-level access checks

This vulnerability requires low privileges (authenticated backend access) and no user interaction, making it relatively straightforward to exploit for any user with backend access. The technical details of the fix can be found in the TYPO3 Security Advisory and associated GitHub commits.

Detection Methods for CVE-2025-59020

Indicators of Compromise

• Unexpected modifications to exclude fields in database records that specific users should not have access to modify
• Backend audit logs showing record creation events with unusual field values for restricted fields
• Discrepancies between user permission assignments and actual data modifications in sensitive tables
• HTTP request logs containing defVals parameters targeting fields outside the user's authorized scope

Detection Strategies

• Review TYPO3 backend access logs for record creation operations containing defVals parameters
• Implement database auditing to track modifications to sensitive exclude fields
• Compare actual field modifications against user permission matrices to identify unauthorized changes
• Monitor for patterns of users modifying fields they do not have explicit access to in their backend user group configuration

Monitoring Recommendations

• Enable detailed logging for all backend record creation and modification operations
• Implement alerting on modifications to critical exclude fields such as admin, disable, or permission-related columns
• Regularly audit user permission configurations against actual database modification patterns
• Deploy web application firewall rules to log requests containing defVals parameters for analysis

How to Mitigate CVE-2025-59020

Immediate Actions Required

• Upgrade TYPO3 CMS installations to the latest patched versions immediately
• Review backend user group configurations to ensure principle of least privilege is enforced
• Audit database records for any unauthorized modifications to exclude fields
• Temporarily restrict backend access to trusted administrators only until patching is complete

Patch Information

TYPO3 has released security patches addressing this vulnerability. The fixes are available in the following commits:

• Patch commit ac3f792
• Patch commit cd11a19
• Patch commit fb98378

Administrators should upgrade to patched versions: 10.4.55+, 11.5.49+, 12.4.41+, 13.4.23+, or 14.0.2+ as applicable. Refer to the official TYPO3 Security Advisory TYPO3-CORE-SA-2026-001 for complete patch details.

Workarounds

• Restrict backend user access to only essential personnel until the patch can be applied
• Review and minimize write permissions for all backend user groups, especially for sensitive database tables
• Implement additional access control layers such as IP-based restrictions for backend access
• Enable comprehensive audit logging to detect any exploitation attempts before patching

# Configuration example: Review and restrict backend user permissions
# In TYPO3 backend, navigate to:
# System > Backend Users > [User Group] > Access Lists

# Ensure exclude fields are properly configured and users have minimal necessary permissions
# Check Tables (modify) and Allowed exclude fields settings for each user group

# Enable detailed backend logging in LocalConfiguration.php
$GLOBALS['TYPO3_CONF_VARS']['BE']['debug'] = true;
$GLOBALS['TYPO3_CONF_VARS']['SYS']['systemLogLevel'] = 0;