diff --git a/csharp/ql/lib/semmle/code/csharp/frameworks/Microsoft.qll b/csharp/ql/lib/semmle/code/csharp/frameworks/Microsoft.qll
index 261b15cd4440..f8e98f423a3e 100644
--- a/csharp/ql/lib/semmle/code/csharp/frameworks/Microsoft.qll
+++ b/csharp/ql/lib/semmle/code/csharp/frameworks/Microsoft.qll
@@ -9,3 +9,16 @@ class MicrosoftNamespace extends Namespace {
     this.hasName("Microsoft")
   }
 }
+
+/** The `Microsoft.Net.Http.Headers.HeaderNames` class. */
+class MicrosoftNetHttpHeadersHeaderNames extends Class {
+  MicrosoftNetHttpHeadersHeaderNames() {
+    this.hasFullyQualifiedName("Microsoft.Net.Http.Headers", "HeaderNames")
+  }
+
+  /** Gets the `XFrameOptions` field. */
+  Field getXFrameOptionsField() { result = this.getField("XFrameOptions") }
+
+  /** Gets the `ContentSecurityPolicy` field. */
+  Field getContentSecurityPolicyField() { result = this.getField("ContentSecurityPolicy") }
+}
diff --git a/csharp/ql/lib/semmle/code/csharp/frameworks/microsoft/AspNetCore.qll b/csharp/ql/lib/semmle/code/csharp/frameworks/microsoft/AspNetCore.qll
index 37b0ff2884f9..91d9bddaa72c 100644
--- a/csharp/ql/lib/semmle/code/csharp/frameworks/microsoft/AspNetCore.qll
+++ b/csharp/ql/lib/semmle/code/csharp/frameworks/microsoft/AspNetCore.qll
@@ -565,6 +565,19 @@ class MicrosoftAspNetCoreHttpHeaderDictionaryExtensions extends RefType {
   Method getSetCommaSeparatedValuesMethod() { result = this.getAMethod("SetCommaSeparatedValues") }
 }
 
+/** The `Microsoft.AspNetCore.Http.IHeaderDictionary` interface. */
+class MicrosoftAspNetCoreHttpIHeaderDictionary extends RefType {
+  MicrosoftAspNetCoreHttpIHeaderDictionary() {
+    this.hasFullyQualifiedName("Microsoft.AspNetCore.Http", "IHeaderDictionary")
+  }
+
+  /** Gets the `XFrameOptions` property. */
+  Property getXFrameOptionsProperty() { result = this.getProperty("XFrameOptions") }
+
+  /** Gets the `ContentSecurityPolicy` property. */
+  Property getContentSecurityPolicyProperty() { result = this.getProperty("ContentSecurityPolicy") }
+}
+
 /** The `Microsoft.AspNetCore.Http.CookieOptions` class. */
 class MicrosoftAspNetCoreHttpCookieOptions extends RefType {
   MicrosoftAspNetCoreHttpCookieOptions() {
diff --git a/csharp/ql/lib/semmle/code/csharp/security/MissingXFrameOptionsQuery.qll b/csharp/ql/lib/semmle/code/csharp/security/MissingXFrameOptionsQuery.qll
new file mode 100644
index 000000000000..41192823dafb
--- /dev/null
+++ b/csharp/ql/lib/semmle/code/csharp/security/MissingXFrameOptionsQuery.qll
@@ -0,0 +1,112 @@
+/** Provides predicates for recognizing clickjacking-related response-header configuration. */
+
+import csharp
+import semmle.code.csharp.dataflow.DataFlow
+import semmle.code.csharp.frameworks.microsoft.AspNetCore
+import semmle.code.csharp.frameworks.system.Web
+
+/** Holds if `name` is the `X-Frame-Options` header name, ignoring case. */
+bindingset[name]
+predicate isXFrameOptionsText(string name) { name.toLowerCase() = "x-frame-options" }
+
+/** Holds if `name` is the enforced `Content-Security-Policy` header name, ignoring case. */
+bindingset[name]
+predicate isContentSecurityPolicyText(string name) {
+  name.toLowerCase() = "content-security-policy"
+}
+
+/**
+ * Holds if `value` contains a `frame-ancestors` directive at the start of a CSP policy or
+ * after a directive or policy separator.
+ */
+bindingset[value]
+predicate containsFrameAncestorsDirective(string value) {
+  value.regexpMatch("(?is)(^|.*[;,])\\s*frame-ancestors(\\s|;|$).*")
+}
+
+private predicate isXFrameOptionsHeaderNameExpr(Expr name) {
+  isXFrameOptionsText(name.stripImplicit().getValue())
+  or
+  name.stripImplicit().(FieldAccess).getTarget() =
+    any(MicrosoftNetHttpHeadersHeaderNames f).getXFrameOptionsField()
+}
+
+private predicate isContentSecurityPolicyHeaderNameExpr(Expr name) {
+  isContentSecurityPolicyText(name.stripImplicit().getValue()) or
+  name.stripImplicit().(FieldAccess).getTarget() =
+    any(MicrosoftNetHttpHeadersHeaderNames f).getContentSecurityPolicyField()
+}
+
+private predicate containsFrameAncestorsDirectiveExpr(Expr value) {
+  containsFrameAncestorsDirective(value.stripImplicit().getValue())
+}
+
+private predicate isDirectResponseHeadersAccess(Expr expr) {
+  exists(PropertyAccess headers, MicrosoftAspNetCoreHttpHttpResponse response |
+    expr.stripImplicit() = headers and headers.getProperty() = response.getHeadersProperty()
+  )
+}
+
+private predicate isCallOnResponseHeadersAccess(Call call) {
+  exists(Expr qualifier |
+    call.(MethodCall).getQualifier() = qualifier or
+    call.(ExtensionMethodCall).getArgument(0) = qualifier or
+    call.(AccessorCall).getQualifier() = qualifier
+  |
+    exists(Expr directAccess |
+      isDirectResponseHeadersAccess(directAccess) and
+      DataFlow::localExprFlow(directAccess, qualifier.stripImplicit())
+    )
+  )
+}
+
+private predicate isClickjackingHeaderCall(MethodCall call) {
+  (
+    call.getTarget() = any(SystemWebHttpResponseClass r).getAppendHeaderMethod() or
+    call.getTarget() = any(SystemWebHttpResponseClass r).getAddHeaderMethod()
+  ) and
+  (
+    isXFrameOptionsHeaderNameExpr(call.getArgumentForName("name"))
+    or
+    isContentSecurityPolicyHeaderNameExpr(call.getArgumentForName("name")) and
+    containsFrameAncestorsDirectiveExpr(call.getArgumentForName("value"))
+  )
+}
+
+private predicate isClickjackingHeaderDictionaryLikeWrite(Call call) {
+  (
+    call.getTarget().hasUndecoratedName(["Append", "Add", "TryAdd"])
+    or
+    call.(IndexerCall).getTarget() instanceof Setter
+  ) and
+  (
+    isXFrameOptionsHeaderNameExpr(call.getArgumentForName("key"))
+    or
+    isContentSecurityPolicyHeaderNameExpr(call.getArgumentForName("key")) and
+    containsFrameAncestorsDirectiveExpr(call.getArgumentForName("value"))
+  )
+}
+
+private predicate isClickjackingPropertyWrite(Call c) {
+  c.getTarget() instanceof Setter and
+  (
+    c.(PropertyCall).getProperty() =
+      any(MicrosoftAspNetCoreHttpIHeaderDictionary dic).getXFrameOptionsProperty()
+    or
+    c.(PropertyCall).getProperty() =
+      any(MicrosoftAspNetCoreHttpIHeaderDictionary dic).getContentSecurityPolicyProperty() and
+    containsFrameAncestorsDirectiveExpr(c.getArgumentForName("value"))
+  )
+}
+
+/** Gets an expression that configures a clickjacking-related response header. */
+Call getAClickjackingHeaderWrite() {
+  isClickjackingHeaderCall(result)
+  or
+  isCallOnResponseHeadersAccess(result) and
+  (
+    isClickjackingHeaderDictionaryLikeWrite(result)
+    or
+    isClickjackingPropertyWrite(result)
+  )
+}
diff --git a/csharp/ql/src/Security Features/CWE-451/MissingXFrameOptions.qhelp b/csharp/ql/src/Security Features/CWE-451/MissingXFrameOptions.qhelp
index 6d5d298c8e43..5f7dd4f3282f 100644
--- a/csharp/ql/src/Security Features/CWE-451/MissingXFrameOptions.qhelp	
+++ b/csharp/ql/src/Security Features/CWE-451/MissingXFrameOptions.qhelp	
@@ -5,9 +5,10 @@
 
 <overview>
 <p>
-Web sites that do not specify the <code>X-Frame-Options</code> 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
+Web sites that do not restrict framing using the <code>X-Frame-Options</code> HTTP header or the
+<code>frame-ancestors</code> Content Security Policy directive 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.
 </p>
 
@@ -17,16 +18,24 @@ unintentionally clicking a button or link on the vulnerable site.
 <p>
 Set the <code>X-Frame-Options</code> HTTP header to <code>DENY</code>, to instruct web browsers to
 block attempts to load the site in a frame. Alternatively, if framing is needed in certain
-circumstances, specify <code>SAMEORIGIN</code> or <code>ALLOW FROM: ...</code> to limit the ability
-to frame the site to pages from the same origin, or from an allowed whitelist of trusted domains.
+circumstances, specify <code>SAMEORIGIN</code> to permit framing by the same origin. The
+<code>frame-ancestors</code> directive in an enforced <code>Content-Security-Policy</code> header
+provides a more flexible alternative. For example, use <code>frame-ancestors 'none'</code> to
+prevent all framing, or use its source list to specify which origins may embed the application.
 </p>
 <p>
-For ASP.NET web applications, the header may be specified either in the <code>Web.config</code>
-file, using the <code>&lt;customHeaders&gt;</code> tag, or within the source code of the
-application using the <code>HttpResponse.AddHeader</code> method. In general, prefer specifying the
-header in the <code>Web.config</code> 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 <code>Application_BeginRequest</code> method in the <code>global.asax</code> file.
+For ASP.NET Framework applications, the header may be specified either in the
+<code>Web.config</code> file, using the <code>&lt;customHeaders&gt;</code> tag, or within the source
+code of the application using the <code>HttpResponse.AddHeader</code> method. In general, prefer
+specifying the header in the <code>Web.config</code> 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 <code>Application_BeginRequest</code> method in the
+<code>global.asax</code> file.
+</p>
+<p>
+For ASP.NET Core applications, set the header on <code>HttpResponse.Headers</code>. This can be
+done using the header dictionary's indexer or its <code>Append</code>, <code>Add</code>, or
+<code>TryAdd</code> methods.
 </p>
 
 </recommendation>
@@ -41,11 +50,17 @@ The following example shows how to specify the <code>X-Frame-Options</code> head
 
 <p>
 This next example shows how to specify the <code>X-Frame-Options</code> header within the
-<code>global.asax</code> file for ASP.NET application:
+<code>global.asax</code> file for an ASP.NET application:
 </p>
 
 <sample src="MissingXFrameOptions.cs" />
 
+<p>
+The following ASP.NET Core example uses an enforced Content Security Policy to disallow framing:
+</p>
+
+<sample src="MissingXFrameOptionsAspNetCore.cs" />
+
 </example>
 <references>
 
@@ -57,6 +72,10 @@ OWASP:
 Mozilla:
 <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Frame-Options">X-Frame-Options</a>
 </li>
+<li>
+Mozilla:
+<a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/frame-ancestors">Content-Security-Policy: frame-ancestors</a>
+</li>
 
 </references>
 </qhelp>
diff --git a/csharp/ql/src/Security Features/CWE-451/MissingXFrameOptions.ql b/csharp/ql/src/Security Features/CWE-451/MissingXFrameOptions.ql
index 1b647457e7c8..cc3612ce89c1 100644
--- a/csharp/ql/src/Security Features/CWE-451/MissingXFrameOptions.ql	
+++ b/csharp/ql/src/Security Features/CWE-451/MissingXFrameOptions.ql	
@@ -1,7 +1,8 @@
 /**
- * @name Missing X-Frame-Options HTTP header
- * @description If the 'X-Frame-Options' setting is not provided, a malicious user may be able to
- *              overlay their own UI on top of the site by using an iframe.
+ * @name Missing clickjacking protection
+ * @description If neither the 'X-Frame-Options' header nor a Content Security Policy
+ *              'frame-ancestors' directive is provided, a malicious user may be able to overlay
+ *              their own UI on top of the site by using an iframe.
  * @kind problem
  * @problem.severity error
  * @security-severity 7.5
@@ -14,7 +15,7 @@
 
 import csharp
 import semmle.code.asp.WebConfig
-import semmle.code.csharp.frameworks.system.Web
+import semmle.code.csharp.security.MissingXFrameOptionsQuery
 
 XmlElement getAWebConfigRoot(WebConfigXml webConfig) {
   result = webConfig.getARootElement()
@@ -28,9 +29,10 @@ XmlElement getAWebConfigRoot(WebConfigXml webConfig) {
 }
 
 /**
- * Holds if the `Web.config` file `webConfig` adds an `X-Frame-Options` header.
+ * Holds if the `Web.config` file `webConfig` adds an `X-Frame-Options` header or a
+ * `Content-Security-Policy` header containing a `frame-ancestors` directive.
  */
-predicate hasWebConfigXFrameOptions(WebConfigXml webConfig) {
+predicate hasWebConfigClickjackingProtection(WebConfigXml webConfig) {
   // Looking for an entry in `webConfig` that looks like this:
   // ```xml
   // <system.webServer>
@@ -42,29 +44,30 @@ predicate hasWebConfigXFrameOptions(WebConfigXml webConfig) {
   // </system.webServer>
   // ```
   // This can also be in a `location`
-  getAWebConfigRoot(webConfig)
-      .getAChild("system.webServer")
-      .getAChild("httpProtocol")
-      .getAChild("customHeaders")
-      .getAChild("add")
-      .getAttributeValue("name") = "X-Frame-Options"
+  exists(XmlElement add, string name |
+    add =
+      getAWebConfigRoot(webConfig)
+          .getAChild("system.webServer")
+          .getAChild("httpProtocol")
+          .getAChild("customHeaders")
+          .getAChild("add") and
+    name = add.getAttributeValue("name") and
+    (
+      isXFrameOptionsText(name)
+      or
+      isContentSecurityPolicyText(name) and
+      containsFrameAncestorsDirective(add.getAttributeValue("value"))
+    )
+  )
 }
 
 /**
- * Holds if there exists a call to `AddHeader` or `AppendHeader` adding the `X-Frame-Options`
- * header.
+ * Holds if code configures a clickjacking protection response header.
  */
-predicate hasCodeXFrameOptions() {
-  exists(MethodCall call |
-    call.getTarget() = any(SystemWebHttpResponseClass r).getAppendHeaderMethod() or
-    call.getTarget() = any(SystemWebHttpResponseClass r).getAddHeaderMethod()
-  |
-    call.getArgumentForName("name").getValue() = "X-Frame-Options"
-  )
-}
+predicate hasCodeClickjackingProtection() { exists(getAClickjackingHeaderWrite()) }
 
 from WebConfigXml webConfig
 where
-  not hasWebConfigXFrameOptions(webConfig) and
-  not hasCodeXFrameOptions()
-select webConfig, "Configuration file is missing the X-Frame-Options setting."
+  not hasWebConfigClickjackingProtection(webConfig) and
+  not hasCodeClickjackingProtection()
+select webConfig, "Configuration file is missing clickjacking protection."
diff --git a/csharp/ql/src/Security Features/CWE-451/MissingXFrameOptionsAspNetCore.cs b/csharp/ql/src/Security Features/CWE-451/MissingXFrameOptionsAspNetCore.cs
new file mode 100644
index 000000000000..f735a8f0ae7c
--- /dev/null
+++ b/csharp/ql/src/Security Features/CWE-451/MissingXFrameOptionsAspNetCore.cs	
@@ -0,0 +1,8 @@
+void Configure(IApplicationBuilder app)
+{
+    app.Use(async (context, next) =>
+    {
+        context.Response.Headers["Content-Security-Policy"] = "frame-ancestors 'none'";
+        await next();
+    });
+}
diff --git a/csharp/ql/src/change-notes/2026-09-10-missing-x-frame-options.md b/csharp/ql/src/change-notes/2026-09-10-missing-x-frame-options.md
new file mode 100644
index 000000000000..fe62433ec70a
--- /dev/null
+++ b/csharp/ql/src/change-notes/2026-09-10-missing-x-frame-options.md
@@ -0,0 +1,6 @@
+---
+category: minorAnalysis
+---
+* The `cs/web/missing-x-frame-options` query now recognizes clickjacking protection configured
+  through ASP.NET Core response headers and enforced Content Security Policy `frame-ancestors`
+  directives.
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/CodeAddedHeader/MissingXFrameOptions.qlref b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/CodeAddedHeader/MissingXFrameOptions.qlref
index d0d38c4b0117..b8a963200e57 100644
--- a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/CodeAddedHeader/MissingXFrameOptions.qlref	
+++ b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/CodeAddedHeader/MissingXFrameOptions.qlref	
@@ -1,2 +1 @@
-query: Security Features/CWE-451/MissingXFrameOptions.ql
-postprocess: utils/test/InlineExpectationsTestQuery.ql
+Security Features/CWE-451/MissingXFrameOptions.ql
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/HeaderWrites.cs b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/HeaderWrites.cs
new file mode 100644
index 000000000000..907de6823982
--- /dev/null
+++ b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/HeaderWrites.cs	
@@ -0,0 +1,51 @@
+using System.Collections.Generic;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Net.Http.Headers;
+using AspNetCoreHttpContext = Microsoft.AspNetCore.Http.HttpContext;
+
+public class HeaderWrites
+{
+    public void AspNetCoreResponseHeaders(AspNetCoreHttpContext context)
+    {
+        context.Response.Headers.Append(HeaderNames.XFrameOptions, "DENY"); // $ Alert
+        context.Response.Headers.Add("x-frame-options", "SAMEORIGIN"); // $ Alert
+        context.Response.Headers.TryAdd(
+            HeaderNames.ContentSecurityPolicy,
+            "default-src 'self'; FrAmE-AnCeStOrS 'none'"); // $ Alert
+
+        context.Response.Headers["X-Frame-Options"] = "DENY"; // $ Alert
+        context.Response.Headers["Content-Security-Policy"] = // $ Alert
+            "default-src 'self'; frame-ancestors 'none'";
+        context.Response.Headers.XFrameOptions = "DENY"; // $ Alert
+        context.Response.Headers.ContentSecurityPolicy = // $ Alert
+            "default-src 'self'; frame-ancestors 'self'";
+        context.Response.Headers["Content-Security-Policy"] = // $ Alert
+            "default-src 'self', frame-ancestors 'none'";
+
+        IHeaderDictionary responseHeaders = context.Response.Headers;
+        responseHeaders.Append("X-Frame-Options", "DENY"); // $ Alert
+    }
+
+    public void IgnoredHeaderWrites(AspNetCoreHttpContext context)
+    {
+        context.Request.Headers["X-Frame-Options"] = "DENY";
+
+        IHeaderDictionary reassignedHeaders = context.Response.Headers;
+        reassignedHeaders = context.Request.Headers;
+        reassignedHeaders["X-Frame-Options"] = "DENY";
+
+        var standaloneHeaders = new HeaderDictionary();
+        standaloneHeaders.Append("X-Frame-Options", "DENY");
+        standaloneHeaders["Content-Security-Policy"] = "frame-ancestors 'none'";
+
+        context.Response.Headers["Content-Security-Policy-Report-Only"] =
+            "frame-ancestors 'none'";
+        context.Response.Headers.ContentSecurityPolicyReportOnly = "frame-ancestors 'none'";
+        context.Response.Headers["X-Content-Security-Policy"] = "frame-ancestors 'none'";
+        context.Response.Headers["Content-Security-Policy"] = "default-src 'self'";
+        context.Response.Headers["Content-Security-Policy"] =
+            "report-uri https://example.test/frame-ancestors";
+        context.Response.Headers["Content-Security-Policy"] =
+            "default-src 'self'; not-frame-ancestors 'none'";
+    }
+}
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/HeaderWrites.expected b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/HeaderWrites.expected
new file mode 100644
index 000000000000..163cdda95910
--- /dev/null
+++ b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/HeaderWrites.expected	
@@ -0,0 +1,9 @@
+| HeaderWrites.cs:10:9:10:74 | call to method Append | A clickjacking-related response header is configured here. |
+| HeaderWrites.cs:11:9:11:69 | call to method Add | A clickjacking-related response header is configured here. |
+| HeaderWrites.cs:12:9:14:57 | call to method TryAdd<String,StringValues> | A clickjacking-related response header is configured here. |
+| HeaderWrites.cs:16:9:16:51 | access to indexer | A clickjacking-related response header is configured here. |
+| HeaderWrites.cs:17:9:17:59 | access to indexer | A clickjacking-related response header is configured here. |
+| HeaderWrites.cs:19:9:19:46 | access to property XFrameOptions | A clickjacking-related response header is configured here. |
+| HeaderWrites.cs:20:9:20:54 | access to property ContentSecurityPolicy | A clickjacking-related response header is configured here. |
+| HeaderWrites.cs:22:9:22:59 | access to indexer | A clickjacking-related response header is configured here. |
+| HeaderWrites.cs:26:9:26:57 | call to method Append | A clickjacking-related response header is configured here. |
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/HeaderWrites.ql b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/HeaderWrites.ql
new file mode 100644
index 000000000000..607510cd1111
--- /dev/null
+++ b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/HeaderWrites.ql	
@@ -0,0 +1,12 @@
+/**
+ * @kind problem
+ * @id cs/test/clickjacking-header-write
+ * @problem.severity warning
+ */
+
+import csharp
+import semmle.code.csharp.security.MissingXFrameOptionsQuery
+
+from Expr write
+where write = getAClickjackingHeaderWrite()
+select write, "A clickjacking-related response header is configured here."
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/HeaderWrites.qlref b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/HeaderWrites.qlref
new file mode 100644
index 000000000000..a2d35d0adb5b
--- /dev/null
+++ b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/HeaderWrites.qlref	
@@ -0,0 +1,2 @@
+query: HeaderWrites.ql
+postprocess: utils/test/InlineExpectationsTestQuery.ql
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/MissingXFrameOptions.expected b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/MissingXFrameOptions.expected
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/MissingXFrameOptions.qlref b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/MissingXFrameOptions.qlref
new file mode 100644
index 000000000000..b8a963200e57
--- /dev/null
+++ b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/MissingXFrameOptions.qlref	
@@ -0,0 +1 @@
+Security Features/CWE-451/MissingXFrameOptions.ql
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/Web.config b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/Web.config
new file mode 100644
index 000000000000..484daccbf3a4
--- /dev/null
+++ b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/Web.config	
@@ -0,0 +1,2 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<configuration />
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/options b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/options
new file mode 100644
index 000000000000..ce3f295ed117
--- /dev/null
+++ b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/HeaderWrites/options	
@@ -0,0 +1,3 @@
+semmle-extractor-options: /nostdlib /noconfig
+semmle-extractor-options: --load-sources-from-project:${testdir}/../../../../../resources/stubs/_frameworks/Microsoft.NETCore.App/Microsoft.NETCore.App.csproj
+semmle-extractor-options: --load-sources-from-project:${testdir}/../../../../../resources/stubs/_frameworks/Microsoft.AspNetCore.App/Microsoft.AspNetCore.App.csproj
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/NoHeader/MissingXFrameOptions.expected b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/NoHeader/MissingXFrameOptions.expected
index 74dfb6fc2f47..d1708140c9d7 100644
--- a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/NoHeader/MissingXFrameOptions.expected	
+++ b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/NoHeader/MissingXFrameOptions.expected	
@@ -1 +1 @@
-| Web.config:0:0:0:0 | Web.config | Configuration file is missing the X-Frame-Options setting. |
+| Web.config:0:0:0:0 | Web.config | Configuration file is missing clickjacking protection. |
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/Csp.Web.config b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/Csp.Web.config
new file mode 100644
index 000000000000..733792aadd8d
--- /dev/null
+++ b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/Csp.Web.config	
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<configuration>
+  <system.webServer>
+    <httpProtocol>
+      <customHeaders>
+        <add name="cOnTeNt-SeCuRiTy-PoLiCy" value="default-src 'self'; FRAME-ANCESTORS 'none'" />
+      </customHeaders>
+    </httpProtocol>
+  </system.webServer>
+</configuration>
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/CspSubstring.Web.config b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/CspSubstring.Web.config
new file mode 100644
index 000000000000..caf093f9ecbe
--- /dev/null
+++ b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/CspSubstring.Web.config	
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<configuration>
+  <system.webServer>
+    <httpProtocol>
+      <customHeaders>
+        <add name="Content-Security-Policy" value="report-uri https://example.test/frame-ancestors" />
+      </customHeaders>
+    </httpProtocol>
+  </system.webServer>
+</configuration>
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/MissingXFrameOptions.expected b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/MissingXFrameOptions.expected
index e69de29bb2d1..31aad4a5216f 100644
--- a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/MissingXFrameOptions.expected	
+++ b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/MissingXFrameOptions.expected	
@@ -0,0 +1,2 @@
+| CspSubstring.Web.config:0:0:0:0 | CspSubstring.Web.config | Configuration file is missing clickjacking protection. |
+| PrefixedCsp.Web.config:0:0:0:0 | PrefixedCsp.Web.config | Configuration file is missing clickjacking protection. |
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/MissingXFrameOptions.qlref b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/MissingXFrameOptions.qlref
index d0d38c4b0117..b8a963200e57 100644
--- a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/MissingXFrameOptions.qlref	
+++ b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/MissingXFrameOptions.qlref	
@@ -1,2 +1 @@
-query: Security Features/CWE-451/MissingXFrameOptions.ql
-postprocess: utils/test/InlineExpectationsTestQuery.ql
+Security Features/CWE-451/MissingXFrameOptions.ql
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/PrefixedCsp.Web.config b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/PrefixedCsp.Web.config
new file mode 100644
index 000000000000..334b63ce5b0e
--- /dev/null
+++ b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/PrefixedCsp.Web.config	
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<configuration>
+  <system.webServer>
+    <httpProtocol>
+      <customHeaders>
+        <add name="X-Content-Security-Policy" value="frame-ancestors 'none'" />
+      </customHeaders>
+    </httpProtocol>
+  </system.webServer>
+</configuration>
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/Web.config b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/Web.config
index 78f6c30a819f..74c0fa10fd27 100644
--- a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/Web.config	
+++ b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeader/Web.config	
@@ -5,7 +5,7 @@
   <system.webServer>
     <httpProtocol>
       <customHeaders>
-        <add name="X-Frame-Options" value="SAMEORIGIN" />
+        <add name="x-frame-options" value="SAMEORIGIN" />
       </customHeaders>
     </httpProtocol>
   </system.webServer>
diff --git a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeaderInLocation/MissingXFrameOptions.qlref b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeaderInLocation/MissingXFrameOptions.qlref
index d0d38c4b0117..b8a963200e57 100644
--- a/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeaderInLocation/MissingXFrameOptions.qlref	
+++ b/csharp/ql/test/query-tests/Security Features/CWE-451/MissingXFrameOptions/WebConfigAddedHeaderInLocation/MissingXFrameOptions.qlref	
@@ -1,2 +1 @@
-query: Security Features/CWE-451/MissingXFrameOptions.ql
-postprocess: utils/test/InlineExpectationsTestQuery.ql
+Security Features/CWE-451/MissingXFrameOptions.ql