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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.

PUBLISHED Reserved 2026-06-28 | Published 2026-06-28 | Updated 2026-06-28 | Assigner VulnCheck




HIGH: 7.2CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
HIGH: 8.6CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Problem types

Improper Privilege Management

Product status

Default status
affected

Any version
affected

Credits

ashdfrkl finder

References

github.com/...ploitarium/tree/main/mybb-limited-acp-to-admin (Proof of Concept) exploit third-party-advisory

www.vulncheck.com/...ed-acp-user-management-to-administrator (VulnCheck Advisory: MyBB - Privilege Escalation from Limited ACP User Management to Administrator) third-party-advisory

cve.org (CVE-2026-58054)

nvd.nist.gov (CVE-2026-58054)

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