CVE-2025-59535: 
C# vulnerability analysis and mitigation

DNN (formerly DotNetNuke), an open-source web content management platform in the Microsoft ecosystem, disclosed a vulnerability (CVE-2025-59535) that allows arbitrary themes to be loaded through query parameters. The vulnerability was discovered and reported by 6TELOIV, and affects versions prior to 10.1.0. The issue was patched in version 10.1.0 with remediation developed by bdukes and reviewed by valadas (GitHub Advisory).

The vulnerability has been assigned a CVSS v3.1 base score of 6.5 (Medium) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L. The issue is associated with multiple CWE classifications including CWE-20 (Improper Input Validation), CWE-200 (Exposure of Sensitive Information), and CWE-829 (Inclusion of Functionality from Untrusted Control Sphere). The vulnerability allows attackers to exploit the query parameter handling in the theme loading mechanism (GitHub Source).

If an installed theme contains a vulnerability, even if it's not actively used on any page, it could be loaded on unsuspecting clients without the site owner's knowledge. This could potentially lead to both server-side and client-side arbitrary code execution, depending on the vulnerabilities present in the loaded theme. The risk is particularly significant for sites with multiple unused or outdated themes that haven't been maintained (GitHub Advisory).

The vulnerability has been patched in DNN version 10.1.0, where the functionality is disabled by default. A setting has been introduced in the Security module to activate the functionality if needed. Organizations should upgrade to version 10.1.0 or later to address this vulnerability. Additionally, it's recommended to regularly review and remove unused themes to reduce the potential attack surface (GitHub Advisory).