CVE-2026-45115High· 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

0.29% · p22

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 Buddy/Ignore component does not sanitize usernames correctly, allowing attackers to perform JavaScript code injection through a specially crafted username. The User CP Buddy/Ignore list and the Select Buddies list in Private Messages pass usernames through htmlspecialchars_uni(), which may leave single quotes unescaped. The payload is triggered when a victim chooses Yes in Please Confirm while removing the username in usercp.php, or selects the username through the onclick handler in the xmlhttp.php Select Buddies popup. The uniquely identifying implementation details include Private Messages Select Buddies list, and unescaped single quotes. 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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