CVE-2021-41866 Explained : Impact and Mitigation

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.

Understanding CVE-2021-41866

MyBB version before 1.8.28 is affected by a stored XSS vulnerability due to improper handling of Template Name values in the Admin CP's theme management.

What is CVE-2021-41866?

This CVE refers to a stored XSS vulnerability in MyBB versions prior to 1.8.28, which can allow attackers to inject malicious scripts into the Admin CP's theme management, exploiting the improper escaping of Template Name values.

The Impact of CVE-2021-41866

The vulnerability can lead to stored cross-site scripting attacks, enabling threat actors to execute arbitrary code in the context of the affected user's session, potentially compromising sensitive data and performing malicious actions.

Technical Details of CVE-2021-41866

MyBB's vulnerability details and its impact on systems.

Vulnerability Description

CVE ID: CVE-2021-41866
Type: Stored XSS
Severity: Medium
Vector: Network
Attack Complexity: Low
Authentication: None required
CVSS Score: 4.3 (Medium)

Affected Systems and Versions

Affected Version: MyBB before 1.8.28
Product: Not applicable
Vendor: Not applicable

Exploitation Mechanism

The vulnerability arises from the lack of proper escaping of Template Name values in the Admin CP's theme management, allowing adversaries to inject and execute malicious scripts within the system.

Mitigation and Prevention

Protecting systems against CVE-2021-41866.

Immediate Steps to Take

Update MyBB to version 1.8.28 or the latest release to patch the vulnerability.
Ensure proper input validation and output encoding to mitigate XSS risks.
Monitor and sanitize user inputs to prevent script injection attacks.

Long-Term Security Practices

Regularly audit and update software to address security flaws promptly.
Educate users on safe browsing practices and potential risks of XSS attacks.

Patching and Updates

Stay informed about security advisories from MyBB.
Apply security patches and updates promptly to mitigate known vulnerabilities.