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MyBB EUVDEUVD-2026-39974

| CVE-2026-58054 HIGH
Improper Privilege Management (CWE-269)
2026-06-28 VulnCheck GHSA-cvxv-xfvj-jmc4
Privilege Escalation Mybb
8.6
CVSS 4.0 · Vendor: VulnCheck
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Severity by source

Vendor (VulnCheck) PRIMARY
8.6 HIGH
CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
7.2 HIGH

Reachable over the network via the ACP but requires an existing privileged limited-admin account (PR:H); no user interaction, low complexity, and full takeover yields high C/I/A with unchanged scope.

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

Primary rating from Vendor (VulnCheck).

CVSS VectorVendor: VulnCheck

CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack Vector
Network
Attack Complexity
Low
Privileges Required
High
User Interaction
None
Scope
X

Lifecycle Timeline

2
Analysis Generated
Jun 28, 2026 - 02:31 vuln.today
CVSS changed
Jun 28, 2026 - 02:22 NVD
7.2 (HIGH) 8.6 (HIGH)

DescriptionCVE.org

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.

AnalysisAI

Privilege escalation in MyBB 1.8.40 lets a limited Admin Control Panel (ACP) user who holds only the delegated user-management permission promote any account into the Administrators usergroup (gid 4), gaining the full Administrator permission set. The flaw stems from the user module exposing the Administrators group as an assignable option while the datahandler's verify_usergroup() unconditionally returns true, performing no authorization check on the target group. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Authenticate as limited ACP user
Delivery
Open user module create/edit form
Exploit
Select Administrators group (gid 4)
Execution
verify_usergroup() returns true, save
Impact
Account gains full Administrator permissions
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Vulnerability AssessmentAI

Exploitation Exploitation requires an existing authenticated MyBB Admin Control Panel account that holds the delegated user-management permission (the ability to create or edit users via the user module); this is the exact precondition reflected by PR:H in the CVSS vector. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:N) scored 8.6 reflects network reachability, low complexity, no user interaction, and high impact on confidentiality, integrity, and availability - but critically requires high privileges (PR:H), meaning the attacker must already be a trusted, authenticated limited ACP admin. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario A forum operator grants a moderator a limited ACP account with only the user-management permission to handle routine account edits. That moderator opens the user module, edits their own (or a confederate's) account, selects the Administrators group from the still-available usergroup dropdown, and saves - instantly gaining full administrator control over the board. …
Remediation No vendor-released patch version is identified in the available data, so monitor MyBB's official releases and the VulnCheck advisory (https://www.vulncheck.com/advisories/mybb-privilege-escalation-from-limited-acp-user-management-to-administrator) for an upstream fix and upgrade as soon as a patched 1.8.x release is published. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

24 hours: Audit all delegated Admin Control Panel users with user-management permissions and immediately revoke or restrict permissions for non-critical roles. …

Sign in for detailed remediation steps and compensating controls.

Threat intelligence, references, and detailed analysis are available after sign-in.

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EUVD-2026-39974 vulnerability details – vuln.today
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