Vulnerability · Published Aug 18, 2026 · Assigned by GitHub_M

CVE-2026-45115MyBB: Buddy/ignore list username XSS

High 8.7

In plain English

A high-severity cross-site scripting in mybb from mybb. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 36% of all known vulnerabilities).

Severity (CVSS 3.1)8.7High

Exploit odds (30 days)0.4%top 63.9% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

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.

Affected products (as reported)

Vendor	Product	Versions
mybb	mybb	< 1.8.40

Weakness: CWE-79 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N

References

https://github.com/mybb/mybb/security/advisories/GHSA-p766-qqxv-rfc2 x_refsource_CONFIRM
https://github.com/mybb/mybb/releases/tag/mybb_1840 x_refsource_MISC
https://mybb.com/versions/1.8.40 x_refsource_MISC