CodeQL documentation

Missing X-Frame-Options HTTP header

ID: cs/web/missing-x-frame-options
Kind: problem
Severity: error
Precision: high
   - security
   - external/cwe/cwe-451
   - external/cwe/cwe-829
Query suites:
   - csharp-code-scanning.qls
   - csharp-security-extended.qls
   - csharp-security-and-quality.qls

Click to see the query in the CodeQL repository

Web sites that do not specify the X-Frame-Options HTTP header may be vulnerable to UI redress attacks (“clickjacking”). In these attacks, the vulnerable site is loaded in a frame on an attacker-controlled site which uses opaque or transparent layers to trick the user into unintentionally clicking a button or link on the vulnerable site.


Set the X-Frame-Options HTTP header to DENY, to instruct web browsers to block attempts to load the site in a frame. Alternatively, if framing is needed in certain circumstances, specify SAMEORIGIN or ALLOW FROM: ... to limit the ability to frame the site to pages from the same origin, or from an allowed whitelist of trusted domains.

For ASP.NET web applications, the header may be specified either in the Web.config file, using the <customHeaders> tag, or within the source code of the application using the HttpResponse.AddHeader method. In general, prefer specifying the header in the Web.config file to ensure it is added to all requests. If adding it to the source code, ensure that it is added unconditionally to all requests. For example, add the header in the Application_BeginRequest method in the global.asax file.


The following example shows how to specify the X-Frame-Options header within the Web.config file for ASP.NET:

<?xml version="1.0" encoding="utf-8" ?>
        <add name="X-Frame-Options" value="SAMEORIGIN" />

This next example shows how to specify the X-Frame-Options header within the global.asax file for ASP.NET application:

protected void Application_BeginRequest(object sender, EventArgs e)
    HttpContext.Current.Response.AddHeader("X-Frame-Options", "DENY");