diff --git a/chrome/browser/ui/browser.cc b/chrome/browser/ui/browser.cc
index 8ad020fac68de..99fa1d403c03c 100644
--- a/chrome/browser/ui/browser.cc
+++ b/chrome/browser/ui/browser.cc
@@ -1918,6 +1918,17 @@ WebContents* Browser::OpenURLFromTab(
           load_params.transition_type = params.transition;
           load_params.referrer =
               content::Referrer(params.referrer.url, params.referrer.policy);
+          // SECURITY: This branch is reachable from a (compromised) renderer
+          // via FrameHost::OpenURL with disposition NEW_SPLIT_VIEW. Propagate
+          // the renderer-initiated/initiator fields so the partner-tab
+          // navigation is not laundered into a browser-initiated one (which
+          // would defeat Sec-Fetch-Site, SameSite=Strict, and the
+          // GetVisibleEntry pending-URL spoof guard).
+          load_params.is_renderer_initiated = params.is_renderer_initiated;
+          load_params.initiator_origin = params.initiator_origin;
+          load_params.initiator_process_id = params.initiator_process_id;
+          load_params.source_site_instance = params.source_site_instance;
+          load_params.has_user_gesture = params.user_gesture;
           tab->GetContents()->GetController().LoadURLWithParams(load_params);
           return source;
         }