Overview
CVE-2005-4398 describes a cross-site scripting (XSS) vulnerability in lemoon 2.0 and earlier where remote attackers could inject arbitrary web script or HTML via unspecified search parameters (potentially the q parameter). The vendor disputes the issue, attributing it to a public site built on lemoon rather than the core product. In modern ASP.NET Core (C#) applications, similar flaws can lead to sensitive data exposure when untrusted input is reflected into HTML or JavaScript, enabling an attacker to steal cookies, session tokens, or display sensitive data through injected scripts. While the lemoon CVE refers to an older CMS, the underlying risk-unencoded user input enabling script execution that can exfiltrate sensitive information-remains a critical concern for web apps, including those built on ASP.NET Core. This guide connects that real-world vulnerability pattern to ASP.NET Core implementations and shows how proper encoding, rendering practices, and defensive headers prevent such exposures.
Affected Versions
N/A (CVE-2005-4398 pertains to lemoon 2.0 and earlier)
Code Fix Example
ASP.NET Core API Security Remediation
using System.Text.Encodings.Web;
using Microsoft.AspNetCore.Mvc;
namespace DemoApp.Controllers
{
[Route("api/[controller]")]
public class VulnerabilityController : Controller
{
// Vulnerable pattern: building HTML via string concatenation with untrusted input
[HttpGet("vulnerable")]
public IActionResult Vulnerable(string q)
{
var html = "<div>Query: " + q + "</div>";
// Returns raw HTML; if q contains scripts, they execute in the user's browser
return Content(html, "text/html");
}
// Fixed pattern: encode user input before embedding into HTML
[HttpGet("fixed")]
public IActionResult Fixed(string q)
{
var encoded = HtmlEncoder.Default.Encode(q);
var html = "<div>Query: " + encoded + "</div>";
return Content(html, "text/html");
}
}
}