CVE-2025-59821: 
C# vulnerability analysis and mitigation

DNN (formerly DotNetNuke), an open-source web content management platform in the Microsoft ecosystem, was found to contain a reflected cross-site scripting (XSS) vulnerability identified as CVE-2025-59821. The vulnerability was discovered and disclosed on September 23, 2025, affecting all versions prior to 10.1.0 (GitHub Advisory).

The vulnerability stems from insufficient neutralization of characters in DNN's URL/path handling and template rendering system. The application fails to properly encode HTML-meaningful characters in user profiles that are returned to the browser. The vulnerability has been assigned a CVSS v3.1 base score of 6.5 (Medium) with the vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N, indicating network accessibility, low attack complexity, no privileges required, and user interaction required. The vulnerability is classified as CWE-79: Improper Neutralization of Input During Web Page Generation (GitHub Advisory).

The vulnerability allows attackers to cause victims' browsers to interpret attacker-controlled content as part of the page's HTML. This can lead to high confidentiality impact, though integrity and availability are not affected. The attack requires user interaction and is limited to the user's scope (GitHub Advisory).

The vulnerability has been patched in DNN version 10.1.0. Users are advised to upgrade to this version or later to mitigate the risk (GitHub Advisory).