diff --git a/csharp/ql/lib/change-notes/2026-06-12-razor-page-handler-sources.md b/csharp/ql/lib/change-notes/2026-06-12-razor-page-handler-sources.md
new file mode 100644
index 000000000000..aca9d7631cdf
--- /dev/null
+++ b/csharp/ql/lib/change-notes/2026-06-12-razor-page-handler-sources.md
@@ -0,0 +1,4 @@
+---
+category: majorAnalysis
+---
+* Added Razor Page handler method parameters (e.g., `OnGet`, `OnPost`, `OnPostAsync`) as remote flow sources, enabling security queries such as `cs/sql-injection` to detect vulnerabilities in `PageModel` subclasses.
diff --git a/csharp/ql/lib/semmle/code/csharp/security/dataflow/flowsources/Remote.qll b/csharp/ql/lib/semmle/code/csharp/security/dataflow/flowsources/Remote.qll
index aa8c8536556e..68c06a1828de 100644
--- a/csharp/ql/lib/semmle/code/csharp/security/dataflow/flowsources/Remote.qll
+++ b/csharp/ql/lib/semmle/code/csharp/security/dataflow/flowsources/Remote.qll
@@ -13,6 +13,7 @@ private import semmle.code.csharp.frameworks.system.web.ui.WebControls
 private import semmle.code.csharp.frameworks.WCF
 private import semmle.code.csharp.frameworks.microsoft.Owin
 private import semmle.code.csharp.frameworks.microsoft.AspNetCore
+private import semmle.code.csharp.frameworks.Razor
 private import semmle.code.csharp.dataflow.internal.ExternalFlow
 private import semmle.code.csharp.security.dataflow.flowsources.FlowSources
 
@@ -314,6 +315,22 @@ class AspNetCoreActionMethodParameter extends AspNetCoreRemoteFlowSource, DataFl
   override string getSourceType() { result = "ASP.NET Core MVC action method parameter" }
 }
 
+/** A parameter to a Razor Page handler method, viewed as a source of remote user input. */
+class AspNetCorePageHandlerMethodParameter extends AspNetCoreRemoteFlowSource,
+  DataFlow::ParameterNode
+{
+  AspNetCorePageHandlerMethodParameter() {
+    exists(Parameter p |
+      p = this.getParameter() and
+      p.fromSource()
+    |
+      p = any(PageModelClass pm).getAHandlerMethod().getAParameter()
+    )
+  }
+
+  override string getSourceType() { result = "ASP.NET Core Razor Page handler method parameter" }
+}
+
 private class ExternalRemoteFlowSource extends RemoteFlowSource {
   ExternalRemoteFlowSource() { sourceNode(this, "remote") }
 
diff --git a/csharp/ql/test/library-tests/dataflow/flowsources/aspremote/AspRemoteFlowSource.cs b/csharp/ql/test/library-tests/dataflow/flowsources/aspremote/AspRemoteFlowSource.cs
index e554f25f2064..8507d60cd394 100644
--- a/csharp/ql/test/library-tests/dataflow/flowsources/aspremote/AspRemoteFlowSource.cs
+++ b/csharp/ql/test/library-tests/dataflow/flowsources/aspremote/AspRemoteFlowSource.cs
@@ -63,4 +63,32 @@ public abstract class AbstractTestController : Controller
     {
         public void MyActionMethod(string param) { }
     }
+
+    // Razor Page handler tests
+    public class MyPageModel : Microsoft.AspNetCore.Mvc.RazorPages.PageModel
+    {
+        // BAD: handler method parameters are user-controlled
+        public void OnGet(string id) { }
+
+        public void OnPost(string command, int count) { }
+
+        public void OnPostAsync(string data) { }
+
+        public void OnPut(string value) { }
+
+        public void OnDelete(string itemId) { }
+
+        // GOOD: not a handler method (doesn't start with On)
+        public void GetUser(string userId) { }
+
+        // GOOD: marked with NonHandler attribute
+        [Microsoft.AspNetCore.Mvc.RazorPages.NonHandlerAttribute]
+        public void OnGetNonHandler(string param) { }
+    }
+
+    // Subclass of a PageModel subclass
+    public class DerivedPageModel : MyPageModel
+    {
+        public void OnPost(string derivedParam) { }
+    }
 }
diff --git a/csharp/ql/test/library-tests/dataflow/flowsources/aspremote/aspRemoteFlowSource.expected b/csharp/ql/test/library-tests/dataflow/flowsources/aspremote/aspRemoteFlowSource.expected
index d729eb939d28..ef7a8f3cd784 100644
--- a/csharp/ql/test/library-tests/dataflow/flowsources/aspremote/aspRemoteFlowSource.expected
+++ b/csharp/ql/test/library-tests/dataflow/flowsources/aspremote/aspRemoteFlowSource.expected
@@ -14,3 +14,10 @@ remoteFlowSources
 | AspRemoteFlowSource.cs:54:69:54:82 | mapDeleteParam |
 | AspRemoteFlowSource.cs:56:41:56:44 | item |
 | AspRemoteFlowSource.cs:64:43:64:47 | param |
+| AspRemoteFlowSource.cs:71:34:71:35 | id |
+| AspRemoteFlowSource.cs:73:35:73:41 | command |
+| AspRemoteFlowSource.cs:73:48:73:52 | count |
+| AspRemoteFlowSource.cs:75:40:75:43 | data |
+| AspRemoteFlowSource.cs:77:34:77:38 | value |
+| AspRemoteFlowSource.cs:79:37:79:42 | itemId |
+| AspRemoteFlowSource.cs:92:35:92:46 | derivedParam |