CVE-2026-58054

Description

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.

References

• https://github.com/bikini/exploitarium/tree/main/mybb-limited-acp-to-admin
• https://www.vulncheck.com/advisories/mybb-privilege-escalation-from-limited-acp-user-management-to-administrator