From cd93e1028bb337e0f7e83d8b704f9faa03981932 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Julio=20C=C3=A9sar=20Rocha?=
 <JunielKatarn@users.noreply.github.com>
Date: Mon, 16 Mar 2026 16:09:42 -0700
Subject: [PATCH] Fix unhandled synchronous throw from WebSocket ConnectAsync
 (#15783)

* Fix unhandled synchronous throw from ConnectAsync

(Generated summary)
ConnectAsync can throw synchronously (e.g. WININET_E_INVALID_CA /
0x80072EE1 on certificate validation failure) before returning an
IAsyncAction. Move the call inside the existing try/catch block so
such exceptions are routed through Fail() instead of propagating
unhandled. Add ConnectAsyncThrowsSynchronously unit test to cover
this path.

* Change files

* Add explaining comment

* clang format
---
 ...-a940bd34-f062-4109-b462-3e634bb5ddae.json |  7 ++++
 .../WinRTWebSocketResourceUnitTest.cpp        | 33 +++++++++++++++++++
 .../Networking/WinRTWebSocketResource.cpp     |  9 ++---
 3 files changed, 45 insertions(+), 4 deletions(-)
 create mode 100644 change/react-native-windows-a940bd34-f062-4109-b462-3e634bb5ddae.json

diff --git a/change/react-native-windows-a940bd34-f062-4109-b462-3e634bb5ddae.json b/change/react-native-windows-a940bd34-f062-4109-b462-3e634bb5ddae.json
new file mode 100644
index 00000000000..4032fccc969
--- /dev/null
+++ b/change/react-native-windows-a940bd34-f062-4109-b462-3e634bb5ddae.json
@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "Fix unhandled synchronous throw from ConnectAsync",
+  "packageName": "react-native-windows",
+  "email": "julio.rocha@microsoft.com",
+  "dependentChangeType": "patch"
+}
diff --git a/vnext/Desktop.UnitTests/WinRTWebSocketResourceUnitTest.cpp b/vnext/Desktop.UnitTests/WinRTWebSocketResourceUnitTest.cpp
index ebf8d57e303..fb4367e9103 100644
--- a/vnext/Desktop.UnitTests/WinRTWebSocketResourceUnitTest.cpp
+++ b/vnext/Desktop.UnitTests/WinRTWebSocketResourceUnitTest.cpp
@@ -105,6 +105,39 @@ TEST_CLASS (WinRTWebSocketResourceUnitTest) {
     Assert::IsFalse(connected);
   }
 
+  BEGIN_TEST_METHOD_ATTRIBUTE(ConnectAsyncThrowsSynchronously)
+  END_TEST_METHOD_ATTRIBUTE()
+  TEST_METHOD(ConnectAsyncThrowsSynchronously) {
+    Logger::WriteMessage("Microsoft::React::Test::WinRTWebSocketResourceUnitTest::ConnectAsyncThrowsSynchronously");
+    bool connected = false;
+    string errorMessage;
+    promise<void> donePromise;
+
+    auto imws{winrt::make<MockMessageWebSocket>()};
+    auto mws{imws.as<MockMessageWebSocket>()};
+    // Simulate a synchronous throw from ConnectAsync (e.g. WININET_E_INVALID_CA)
+    // before any IAsyncAction is returned.
+    mws->Mocks.ConnectAsync = [](const Uri &) -> IAsyncAction {
+      throw winrt::hresult_error(winrt::hresult(0x80072EE1), L"Invalid CA");
+    };
+
+    auto rc = make_shared<WinRTWebSocketResource2>(
+        std::move(imws), MockDataWriter{}, CertExceptions{}, Mso::DispatchQueue::MakeSerialQueue());
+    rc->SetOnConnect([&connected]() { connected = true; });
+    rc->SetOnError([&errorMessage, &donePromise](Error &&error) {
+      errorMessage = error.Message;
+      donePromise.set_value();
+    });
+
+    rc->Connect(testUrl, {}, {});
+    rc->Close(CloseCode::Normal, {});
+
+    donePromise.get_future().wait();
+
+    Assert::AreEqual({"[0x80072ee1] Invalid CA"}, errorMessage);
+    Assert::IsFalse(connected);
+  }
+
   BEGIN_TEST_METHOD_ATTRIBUTE(SetRequestHeaderFails)
   END_TEST_METHOD_ATTRIBUTE()
   TEST_METHOD(SetRequestHeaderFails) {
diff --git a/vnext/Shared/Networking/WinRTWebSocketResource.cpp b/vnext/Shared/Networking/WinRTWebSocketResource.cpp
index 123fe196b67..6701b56d4ad 100644
--- a/vnext/Shared/Networking/WinRTWebSocketResource.cpp
+++ b/vnext/Shared/Networking/WinRTWebSocketResource.cpp
@@ -227,11 +227,12 @@ fire_and_forget WinRTWebSocketResource2::PerformConnect(Uri &&uri) noexcept {
       [self = self->shared_from_this(), coUri = std::move(movedUri)]() -> IAsyncAction {
         auto coSelf = self->shared_from_this();
 
-        auto async = coSelf->m_socket.ConnectAsync(coUri);
-        co_await lessthrow_await_adapter<IAsyncAction>{async};
-
-        auto result = async.ErrorCode();
         try {
+          // `ConnectAsync` MAY throw synchronously (e.g. WININET_E_INVALID_CA)
+          auto async = coSelf->m_socket.ConnectAsync(coUri);
+          co_await lessthrow_await_adapter<IAsyncAction>{async};
+
+          auto result = async.ErrorCode();
           if (result >= 0) { // Non-failing HRESULT
             coSelf->m_readyState = ReadyState::Open;