diff --git a/libcef/browser/alloy/alloy_content_browser_client.cc b/libcef/browser/alloy/alloy_content_browser_client.cc
index 9cb1bb96c..1c0679cff 100644
--- a/libcef/browser/alloy/alloy_content_browser_client.cc
+++ b/libcef/browser/alloy/alloy_content_browser_client.cc
@@ -61,6 +61,7 @@
 #include "chrome/browser/profiles/renderer_updater_factory.h"
 #include "chrome/browser/renderer_host/pepper/chrome_browser_pepper_host_factory.h"
 #include "chrome/browser/spellchecker/spell_check_host_chrome_impl.h"
+#include "chrome/common/chrome_content_client.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/google_url_loader_throttle.h"
@@ -1480,6 +1481,31 @@ AlloyContentBrowserClient::GetPluginMimeTypesWithExternalHandlers(
   return mime_types;
 }
 
+bool AlloyContentBrowserClient::ShouldAllowPluginCreation(
+    const url::Origin& embedder_origin,
+    const content::PepperPluginInfo& plugin_info) {
+  if (plugin_info.name == ChromeContentClient::kPDFInternalPluginName) {
+    // Allow embedding the internal PDF plugin in the built-in PDF extension.
+    if (embedder_origin.scheme() == extensions::kExtensionScheme &&
+        embedder_origin.host() == extension_misc::kPdfExtensionId) {
+      return true;
+    }
+
+    // Allow embedding the internal PDF plugin in chrome://print.
+    if (embedder_origin ==
+        url::Origin::Create(GURL(chrome::kChromeUIPrintURL))) {
+      return true;
+    }
+
+    // Only allow the PDF plugin in the known, trustworthy origins that are
+    // allowlisted above.  See also https://crbug.com/520422 and
+    // https://crbug.com/1027173.
+    return false;
+  }
+
+  return true;
+}
+
 CefRefPtr<CefRequestContextImpl> AlloyContentBrowserClient::request_context()
     const {
   return browser_main_parts_->request_context();
diff --git a/libcef/browser/alloy/alloy_content_browser_client.h b/libcef/browser/alloy/alloy_content_browser_client.h
index e6335abd2..948c4d02a 100644
--- a/libcef/browser/alloy/alloy_content_browser_client.h
+++ b/libcef/browser/alloy/alloy_content_browser_client.h
@@ -207,6 +207,9 @@ class AlloyContentBrowserClient : public content::ContentBrowserClient {
   blink::UserAgentMetadata GetUserAgentMetadata() override;
   base::flat_set<std::string> GetPluginMimeTypesWithExternalHandlers(
       content::BrowserContext* browser_context) override;
+  bool ShouldAllowPluginCreation(
+      const url::Origin& embedder_origin,
+      const content::PepperPluginInfo& plugin_info) override;
 
   CefRefPtr<CefRequestContextImpl> request_context() const;
   CefDevToolsDelegate* devtools_delegate() const;
diff --git a/libcef/browser/browser_info_manager.cc b/libcef/browser/browser_info_manager.cc
index 90e4c96f3..68c08241f 100644
--- a/libcef/browser/browser_info_manager.cc
+++ b/libcef/browser/browser_info_manager.cc
@@ -22,6 +22,7 @@
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/common/child_process_host.h"
+#include "content/public/common/url_constants.h"
 #include "extensions/common/constants.h"
 
 namespace {
@@ -122,7 +123,7 @@ bool CefBrowserInfoManager::CanCreateWindow(
   params.user_gesture = user_gesture;
 
   CefRefPtr<CefBrowserHostImpl> browser;
-  if (!MaybeAllowNavigation(opener, params, browser)) {
+  if (!MaybeAllowNavigation(opener, params, browser) || !browser) {
     // Cancel the popup.
     return false;
   }
@@ -366,13 +367,17 @@ bool CefBrowserInfoManager::MaybeAllowNavigation(
   bool is_guest_view = false;
   CefRefPtr<CefBrowserHostImpl> browser =
       extensions::GetOwnerBrowserForHost(opener, &is_guest_view);
-  DCHECK(browser);
-  if (!browser)
-    return false;
+  if (!browser) {
+    // Print preview uses a modal dialog where we don't own the WebContents.
+    // Allow that navigation to proceed.
+    return true;
+  }
 
-  if (is_guest_view && !params.url.SchemeIs(extensions::kExtensionScheme)) {
-    // The PDF viewer will load an extension in the guest view. All other
-    // navigations are passed to the owner browser.
+  if (is_guest_view && !params.url.SchemeIs(extensions::kExtensionScheme) &&
+      !params.url.SchemeIs(content::kChromeUIScheme)) {
+    // The PDF viewer will load the PDF extension in the guest view, and print
+    // preview will load chrome://print in the guest view. All other navigations
+    // are passed to the owner browser.
     CEF_POST_TASK(
         CEF_UIT,
         base::Bind(base::IgnoreResult(&CefBrowserHostImpl::OpenURLFromTab),
diff --git a/libcef/browser/browser_info_manager.h b/libcef/browser/browser_info_manager.h
index e0baa6685..55236b3aa 100644
--- a/libcef/browser/browser_info_manager.h
+++ b/libcef/browser/browser_info_manager.h
@@ -141,7 +141,7 @@ class CefBrowserInfoManager : public content::RenderProcessHostObserver {
 
   // Returns true if the navigation should be allowed to proceed, or false if
   // the navigation will instead be sent via OpenURLFromTab. If allowed,
-  // |browser| will be set to the target browser.
+  // |browser| will be set to the target browser if any.
   bool MaybeAllowNavigation(content::RenderFrameHost* opener,
                             const content::OpenURLParams& params,
                             CefRefPtr<CefBrowserHostImpl>& browser) const;