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Vulnerability record · CVE-2021-41866 · published 26 October 2021

CVE-2021-41866: Mybb cross-site scripting vulnerability

Mybb · Mybb

MyBB before 1.8.28 allows stored XSS because the displayed Template Name value in the Admin CP's theme management is not escaped properly.

5.4 CVSS 3.1 Medium EPSS 0.49% · top 59.0% CWE-79 · Cross-site scripting
5.4CVSS 3.1 base score, v2 3.5
0.49%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
4References
17 Jun 2026Last modified by NVD

Description

MyBB before 1.8.28 allows stored XSS because the displayed Template Name value in the Admin CP's theme management is not escaped properly.

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/mybb/mybb/security/advisories/ Third Party Advisory
https://github.com/mybb/mybb/security/advisories/GHSA-gxhv-r3m5-6qv7 PatchThird Party Advisory
https://github.com/mybb/mybb/security/advisories/ Third Party Advisory
https://github.com/mybb/mybb/security/advisories/GHSA-gxhv-r3m5-6qv7 PatchThird Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

10.0CVE-2011-10018Mybb code injection vulnerabilitymyBB version 1.6.4 was distributed with an unauthorized backdoor embedded in the source code. The backdoor allowed remote attackers to execute arbitr…EPSS 2.9%10.0CVE-2015-8974Mybb merge system sql injection vulnerabilitySQL injection vulnerability in the Group Promotions module in the admin control panel in MyBB (aka MyBulletinBoard) before 1.6.18 and 1.8.x before 1.…EPSS 2.1%10.0CVE-2015-2786Mybb vulnerabilityUnspecified vulnerability in MyBB (aka MyBulletinBoard) before 1.8.4 has unknown attack vectors related to "Group join request notifications sent to …EPSS 1.4%10.0CVE-2011-5133Mybb vulnerabilityUnspecified vulnerability in MyBB before 1.6.5 has unknown impact and attack vectors, related to an "unparsed user avatar in the buddy list."EPSS 1.7%10.0CVE-2006-0218Mybb vulnerabilityMultiple unspecified vulnerabilities in MyBulletinBoard (MyBB) before 1.0.2 have unspecified impact and attack vectors, related to (1) admin/moderate…EPSS 1.2%9.8CVE-2020-22612Mybb code injection vulnerabilityInstaller RCE on settings file write in MyBB before 1.8.22.EPSS 0.73%9.8CVE-2017-16780Mybb cross-site request forgery vulnerabilityThe installer in MyBB before 1.8.13 allows remote attackers to execute arbitrary code by writing to the configuration file.EPSS 5.8%9.8CVE-2016-9402Mybb merge system sql injection vulnerabilitySQL injection vulnerability in the moderation tool in MyBB (aka MyBulletinBoard) before 1.8.7 and MyBB Merge System before 1.8.7 might allow remote a…EPSS 2.1%

Source: NIST National Vulnerability Database (record CVE-2021-41866), CISA KEV, FIRST EPSS (scores of 2026-10-16). This page is refreshed as NVD updates the record.