Csharp: fix cs/web/missing-x-frame-options to also consider location elements

csharp/ql/src/Security Features/CWE-451/MissingXFrameOptions.ql

@@ -16,6 +16,17 @@ import csharp
 import semmle.code.asp.WebConfig
 import semmle.code.csharp.frameworks.system.Web
 
+XmlElement getAWebConfigRoot(WebConfigXml webConfig) {
+  result = webConfig.getARootElement()
+  or
+  result = webConfig.getARootElement().getAChild("location") and
+  (
+    not result.hasAttribute("path") // equivalent to path="."
+    or
+    result.getAttributeValue("path") = ["", "."]
+  )
+}
+
 /**
  * Holds if the `Web.config` file `webConfig` adds an `X-Frame-Options` header.
  */
@@ -30,8 +41,8 @@ predicate hasWebConfigXFrameOptions(WebConfigXml webConfig) {
   //   </httpProtocol>
   // </system.webServer>
   // ```
-  webConfig
-      .getARootElement()
+  // This can also be in a `location`
+  getAWebConfigRoot(webConfig)
       .getAChild("system.webServer")
       .getAChild("httpProtocol")
       .getAChild("customHeaders")

csharp/ql/src/change-notes/2025-10-17-location-in-web-config.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* the `cs/web/missing-x-frame-options` query now correctly handles configuration nested in root `<location>` elements.

csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeaderInLocation/MissingXFrameOptions.cs

@@ -0,0 +1,18 @@
+using System;
+using System.Web;
+
+public class AddXFrameOptions : IHttpHandler
+{
+
+    public void ProcessRequest(HttpContext ctx)
+    {
+    }
+
+    public bool IsReusable
+    {
+        get
+        {
+            return true;
+        }
+    }
+}

csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeaderInLocation/MissingXFrameOptions.qlref

@@ -0,0 +1 @@
+Security Features/CWE-451/MissingXFrameOptions.ql

csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeaderInLocation/Web.config

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<configuration>
+  <location path="." inheritInChildApplications="false">
+    <system.webServer>
+      <httpProtocol>
+        <customHeaders>
+          <add name="X-Frame-Options" value="SAMEORIGIN" />
+        </customHeaders>
+      </httpProtocol>
+    </system.webServer>
+  </location>
+</configuration>

csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeaderInLocation/options

@@ -0,0 +1,3 @@
+semmle-extractor-options: /nostdlib /noconfig
+semmle-extractor-options: --load-sources-from-project:${testdir}/../../../../../resources/stubs/_frameworks/Microsoft.NETCore.App/Microsoft.NETCore.App.csproj
+semmle-extractor-options: ${testdir}/../../../../../resources/stubs/System.Web.cs