My ASP.NET page has an <asp:TextBox /> whose text input is encoded via HttpUtility.HtmlEncode();
The page also contains validators such as <asp:RequiredFieldValidator /> and <asp:CustomValidator /> as well as several AJAX toolkit <toolkit:ValidatorCalloutExtender />
If the user inputs </ as the text in the textbox, a Javascript error
A potentially dangerous Request.Form value was detected
from the client (ctl00$contentPlaceHolder$ucLookup$tbxLastName="</")
happens when the form is submitted. I have tried adding various event handlers such as
protected void Page_PreInit(object sender, EventArgs e){}
protected void Page_Init(object sender, EventArgs e){}
protected void Page_PreLoad(object sender, EventArgs e){}
and setting breakpoints but none of them are hit, leading me to believe the error only happens client-side.
How can I debug this error? Are there any hooks which allow me to intercept the user's input and filter or encode it before it causes this issue?
