MyBB up to 1.8.39 User Data user.php verify_profile_fields code injection

Summaryinfo

A vulnerability marked as critical has been reported in MyBB up to 1.8.39. This vulnerability affects the function UserDataHandler::verify_profile_fields of the file inc/datahandlers/user.php of the component User Data Handler. This manipulation of the argument profile_fields causes code injection. This vulnerability is handled as CVE-2026-45116. The attack can be initiated remotely. There is not any exploit available.

Detailsinfo

A vulnerability has been found in MyBB up to 1.8.39 and classified as critical. Affected by this vulnerability is the function UserDataHandler::verify_profile_fields of the file inc/datahandlers/user.php of the component User Data Handler. The manipulation of the argument profile_fields with an unknown input leads to a code injection vulnerability. The CWE definition for the vulnerability is CWE-94. The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

MyBB is free and open source forum software. Prior to 1.8.40, the user datahandler does not properly validate checkbox and multiselect profile field types, resulting in stored JavaScript code injection. UserDataHandler::verify_profile_fields() only performs the specialized validation when is_array($profile_fields[$field]) is true. A non-array profile_fields[fidX] value instead of the expected profile_fields[fidX][] shape falls through to generic text handling and is stored without verification. The affected value is then rendered directly by member.php and inc/functions_post.php rather than processed by the MyCode parser. The uniquely identifying implementation details include inc/datahandlers/user.php. This issue is fixed in version 1.8.40.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-45116 since 05/08/2026. The exploitation appears to be easy. The attack can be launched remotely. It demands that the victim is doing some kind of user interaction. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 08/18/2026). MITRE ATT&CK project uses the attack technique T1059 for this issue.

By approaching the search of inurl:inc/datahandlers/user.php it is possible to find vulnerable targets with Google Hacking.

Upgrading to version 1.8.40 eliminates this vulnerability.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

• Content Management System

Name

• MyBB

Version

• 1.8.0
• 1.8.1
• 1.8.2
• 1.8.3
• 1.8.4
• 1.8.5
• 1.8.6
• 1.8.7
• 1.8.8
• 1.8.9
• 1.8.10
• 1.8.11
• 1.8.12
• 1.8.13
• 1.8.14
• 1.8.15
• 1.8.16
• 1.8.17
• 1.8.18
• 1.8.19
• 1.8.20
• 1.8.21
• 1.8.22
• 1.8.23
• 1.8.24
• 1.8.25
• 1.8.26
• 1.8.27
• 1.8.28
• 1.8.29
• 1.8.30
• 1.8.31
• 1.8.32
• 1.8.33
• 1.8.34
• 1.8.35
• 1.8.36
• 1.8.37
• 1.8.38
• 1.8.39

License

• open-source

Website

• Product: https://mybb.com/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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