diff --git a/front_end/models/ai_assistance/agents/StylingAgent.ts b/front_end/models/ai_assistance/agents/StylingAgent.ts
index 84358416ec..8142c2d0d4 100644
--- a/front_end/models/ai_assistance/agents/StylingAgent.ts
+++ b/front_end/models/ai_assistance/agents/StylingAgent.ts
@@ -501,6 +501,26 @@ export class StylingAgent extends AiAgent<SDK.DOMModel.DOMNode> {
     return this.context?.getItem() ?? null;
   }
 
+  /**
+   * AI-supplied backendNodeIds resolve via the renderer-process-global
+   * DOMNodeIds map, so a number chosen by the LLM can land on a node inside a
+   * cross-origin in-process subframe. Reject nodes whose ownerDocument origin
+   * differs from the conversation's selected-element origin (mirrors the
+   * guard added to ContextSelectionAgent for network requests).
+   */
+  #isSameOriginAsContext(node: SDK.DOMModel.DOMNode): boolean {
+    const allowedOrigin = this.context?.getOrigin();
+    const doc = node.ownerDocument;
+    if (!doc || !allowedOrigin) {
+      return false;
+    }
+    try {
+      return new URL(doc.documentURL).origin === allowedOrigin;
+    } catch {
+      return false;
+    }
+  }
+
   async #getStyles(elements: number[], properties: string[]): Promise<FunctionCallHandlerResult<unknown>> {
     const widgets: ComputedStyleAiWidget[] = [];
 
@@ -519,6 +539,10 @@ export class StylingAgent extends AiAgent<SDK.DOMModel.DOMNode> {
       if (!resolved) {
         return {error: 'Error: Could not find the element with uid=' + uid};
       }
+      if (!this.#isSameOriginAsContext(resolved)) {
+        // Do not disclose existence of cross-origin nodes to the LLM.
+        return {error: 'Error: Could not find the element with uid=' + uid};
+      }
       const styles = await resolved.domModel().cssModel().getComputedStyle(resolved.id);
       if (!styles) {
         return {error: 'Error: Could not get computed styles.'};
@@ -579,6 +603,9 @@ export class StylingAgent extends AiAgent<SDK.DOMModel.DOMNode> {
     if (!node) {
       return {error: `Error: Could not find the element with backendNodeId=${elementId}`};
     }
+    if (!this.#isSameOriginAsContext(node)) {
+      return {error: `Error: Could not find the element with backendNodeId=${elementId}`};
+    }
 
     Annotations.AnnotationRepository.instance().addElementsAnnotation(annotationMessage, node);