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MyBB EUVDEUVD-2026-61010

| CVE-2026-45122 MEDIUM
Incorrect Authorization (CWE-863)
2026-08-18 GitHub_M
PHP Authentication Bypass Mybb
4.3
CVSS 3.1 · Vendor: GitHub_M
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Severity by source

Vendor (GitHub_M) PRIMARY
4.3 MEDIUM
AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
vuln.today AI
4.3 MEDIUM

Network-accessible with low-privilege auth required (forum account plus one calendar mod right); scope unchanged; impact limited to event relocation with no confidentiality or availability effect.

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

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

Lifecycle Timeline

3
Patch available
Aug 18, 2026 - 17:17 EUVD
Source Code Evidence Fetched
Aug 18, 2026 - 16:52 vuln.today
Analysis Generated
Aug 18, 2026 - 16:52 vuln.today

DescriptionCVE.org

MyBB is free and open source forum software. Prior to 1.8.40, the calendar module does not validate moderation permissions for the destination calendar when moving events. A user with moderation permission for the source calendar can move an event to a calendar where the user has only viewing permission because the do_move action in calendar.php does not check canmoderateevents for the target calendar. The uniquely identifying implementation details include calendar event move, source calendar moderation permission, and destination calendar viewing permission. This issue is fixed in version 1.8.40.

AnalysisAI

Incorrect authorization in MyBB's calendar module prior to version 1.8.40 allows authenticated users holding moderation rights on one calendar to relocate events to calendars where they possess only viewing permissions. The do_move action in calendar.php validated canmoderateevents for the source calendar but omitted the equivalent check for the destination, enabling unauthorized cross-calendar event manipulation. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

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Vulnerability AssessmentAI

Exploitation Exploitation requires an authenticated MyBB user account (PR:L per CVSS - unauthenticated exploitation is not possible). … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 3.1 vector (AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N, score 4.3) accurately characterizes this as a low-severity, network-accessible integrity issue requiring a low-privilege authenticated account. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation Upgrade to MyBB version 1.8.40, which resolves this issue by adding destination-calendar permission validation in `calendar.php` (commit 86ed2058e7f9a2c14828e731f684e997f9bb220c). … Detailed patch versions, workarounds, and compensating controls in full report.
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EUVD-2026-61010 vulnerability details – vuln.today
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