EUVD-2026-61017Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
PR:L reflects mandatory forum authentication; C:L and I:L capture limited private event read/write exposure with no availability impact and unchanged scope.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
Lifecycle Timeline
3DescriptionCVE.org
MyBB is free and open source forum software. Prior to 1.8.40, the calendar module does not verify private event status consistently, allowing users with viewing and moderation permissions to access and moderate private events. The private-event check used by get_events() in inc/functions_calendar.php and the event action is missing from the remaining calendar.php actions, despite the limited-access behavior described in inc/languages/english/calendar.lang.php. This issue is fixed in version 1.8.40.
AnalysisAI
MyBB's calendar module prior to version 1.8.40 exposes private forum events to any authenticated user possessing calendar viewing or moderation permissions, due to seven missing authorization checks across calendar.php action handlers. Authenticated forum members can read and modify private calendar events created by other users - data the event creator intended to restrict exclusively to themselves. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires an authenticated forum account with calendar viewing or moderation permissions (confirmed by PR:L in the CVSS vector). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 5.4 Medium score is well-calibrated: AV:N reflects the web-accessible attack surface, PR:L confirms that a standard authenticated forum account is required, and C:L/I:L accurately represent the bounded scope of impact - private calendar event exposure and potential modification. … 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 1.8.40, which patches all seven missing authorization checks in calendar.php as documented in commit c077e6c29755187c4df78a1e674dd61bc55701b3. … Detailed patch versions, workarounds, and compensating controls in full report. |
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