MyBB up to 1.8.40 User verify_usergroup privileges management

Summaryinfo

A vulnerability was found in MyBB up to 1.8.40. It has been classified as critical. Affected is the function verify_usergroup of the component User Module. Performing a manipulation results in privileges management. This vulnerability is known as CVE-2026-58054. Remote exploitation of the attack is possible. Furthermore, an exploit is available.

Detailsinfo

A vulnerability was found in MyBB up to 1.8.40. It has been classified as critical. This affects the function verify_usergroup of the component User Module. The manipulation with an unknown input leads to a privileges management vulnerability. CWE is classifying the issue as CWE-269. The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

MyBB 1.8.40 does not restrict which usergroup a limited Admin Control Panel user may assign when creating or editing users; the user module offers the Administrators group (gid 4) and its datahandler's verify_usergroup() unconditionally returns true. An admin holding only the delegated user-management permission can assign the Administrators group to an account and escalate to the full Administrator permission set.

The weakness was published by ashdfrkl. The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-58054 since 06/28/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. The exploitation requires an enhanced level of successful authentication. Technical details and a public exploit are known. MITRE ATT&CK project uses the attack technique T1068 for this issue.

The exploit is shared for download at github.com. It is declared as proof-of-concept.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-39974). 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
• 1.8.40

License

• open-source

Website

• Product: https://mybb.com/

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Entryinfo

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

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