CVE-2026-45120Network attack vector

Private event access via missing ownership checks

Published Aug 18, 2026 · Updated Aug 18, 2026

Authorization bypass in the calendar module in MyBB Group MyBB before 1.8.40 allows remote authenticated users to access private events via calendar actions. Several calendar.php handlers load an event by eid and proceed when it exists, but unlike get_events() and the event view they do not reject private events owned by another user. Any account with the relevant viewing or moderation permissions can read and alter another user's private event data, but the published record does not indicate broader forum compromise.

CVSS severity5.4
Medium
EPSS probability0.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authorization bypass in the calendar module in MyBB Group MyBB before 1.8.40 allows remote authenticated users to access private events via calendar actions. Several calendar.php handlers load an event by eid and proceed when it exists, but unlike get_events() and the event view they do not reject private events owned by another user. Any account with the relevant viewing or moderation permissions can read and alter another user's private event data, but the published record does not indicate broader forum compromise.

The record

CVE
CVE-2026-45120
Published
Aug 18, 2026
Updated
Aug 18, 2026
Vendor
MyBB Group
Product
MyBB
Classifications
CWE-639, T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 18, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 18, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.8.40

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

MyBB Group · MyBBversion=< 1.8.40

Published CVSS scores

5.4GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-639Authorization Bypass Through User-Controlled Key
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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