CVE-2026-45116High· 8.7▾ Twilight

MyBB is free and open source forum software

▾ Twilight zone — High severity, or a signal on a lesser flaw

Depth score48/ 100 · Moderate

impact 47.8 · likelihood 0.1 · exploitation 0

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Proof of concept

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Published

Aug 18, 2026

Updated

Sep 8, 2026

CVSS

8.7

Vendor

—

Product

—

CWE

CWE-79

Depth score

48 · Moderate

EPSS

0.30% · p23

Platforms

—

Source

NVD

Vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N

EPSS history

Exploit-prediction probability, daily snapshots since Sep 8.

0.3% → 0.3%

Timeline

Disclosure to exploitation, from the record and what we observed since indexing it.

3 events · 21 days

Aug 18, 2026Published
Disclosed via NVD
Sep 8, 2026Record revised
Last analysed / modified upstream
Sep 8, 2026EPSS first tracked
0.3%

CWE-79 #nvd

Full technical detail▾

Overview

MyBB is free and open source forum software. Prior to 1.8.40, the user datahandler does not properly validate checkbox and multiselect profile field types, resulting in stored JavaScript code injection. UserDataHandler::verify_profile_fields() only performs the specialized validation when is_array($profile_fields[$field]) is true. A non-array profile_fields[fidX] value instead of the expected profile_fields[fidX][] shape falls through to generic text handling and is stored without verification. The affected value is then rendered directly by member.php and inc/functions_post.php rather than processed by the MyCode parser. The uniquely identifying implementation details include inc/datahandlers/user.php. This issue is fixed in version 1.8.40.

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

References

Related vulnerabilities

Connected by shared product, vendor, weakness, or advisory.

#nvd

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