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.
Published: 2026-08-18
Score: 8.7 High
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories

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History

Tue, 18 Aug 2026 18:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Tue, 18 Aug 2026 17:45:00 +0000

Type Values Removed Values Added
First Time appeared Mybb
Mybb mybb
Vendors & Products Mybb
Mybb mybb

Tue, 18 Aug 2026 16:00:00 +0000

Type Values Removed Values Added
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.
Title MyBB: Buddy/ignore list username XSS
Weaknesses CWE-79
References
Metrics cvssV3_1

{'score': 8.7, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-08-18T17:55:22.351Z

Reserved: 2026-05-08T20:08:17.207Z

Link: CVE-2026-45115

cve-icon Vulnrichment

Updated: 2026-08-18T17:55:18.854Z

cve-icon NVD

Status : Received

Published: 2026-08-18T16:17:06.180

Modified: 2026-08-18T18:17:34.010

Link: CVE-2026-45115

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-18T18:00:04Z

Weaknesses