Vulnerabilities !!install!! — X-aspnet-version 4.0.3

April 14, 2026 Classification: Technical Advisory / Hardening Guide

When an ASP.NET application handles a request (e.g., .aspx , .ashx , or MVC routes), the runtime automatically appends a response header similar to: x-aspnet-version 4.0.3 vulnerabilities

protected void Application_PreSendRequestHeaders() or MVC routes)

padbuster https://target.com/page.aspx encryptedVIEWSTATE <block-size> -cookies "ASP.NET_SessionId=..." -encoding Base64 x-aspnet-version 4.0.3 vulnerabilities

When an attacker sees this header, they know the server is running a version of .NET Framework 4.x. If the server is not regularly patched via Windows Update , it may be susceptible to legacy vulnerabilities tied to the 4.0 runtime. 2. Major Known Vulnerabilities

Configure your application to display generic error messages to users, rather than detailed ones that could provide valuable information to attackers.