security: implement deceptive URL detection and disclosure in tool confirmations (#19288)

packages/cli/src/ui/components/messages/ToolConfirmationMessage.test.tsx

@@ -88,6 +88,122 @@ describe('ToolConfirmationMessage', () => {
     unmount();
   });
 
+  it('should display WarningMessage for deceptive URLs in info type', async () => {
+    const confirmationDetails: SerializableConfirmationDetails = {
+      type: 'info',
+      title: 'Confirm Web Fetch',
+      prompt: 'https://täst.com',
+      urls: ['https://täst.com'],
+    };
+
+    const { lastFrame, waitUntilReady, unmount } = renderWithProviders(
+      <ToolConfirmationMessage
+        callId="test-call-id"
+        confirmationDetails={confirmationDetails}
+        config={mockConfig}
+        availableTerminalHeight={30}
+        terminalWidth={80}
+      />,
+    );
+
+    await waitUntilReady();
+
+    const output = lastFrame();
+    expect(output).toContain('Deceptive URL(s) detected');
+    expect(output).toContain('Original: https://täst.com');
+    expect(output).toContain(
+      'Actual Host (Punycode): https://xn--tst-qla.com/',
+    );
+    unmount();
+  });
+
+  it('should display WarningMessage for deceptive URLs in exec type commands', async () => {
+    const confirmationDetails: SerializableConfirmationDetails = {
+      type: 'exec',
+      title: 'Confirm Execution',
+      command: 'curl https://еxample.com',
+      rootCommand: 'curl',
+      rootCommands: ['curl'],
+    };
+
+    const { lastFrame, waitUntilReady, unmount } = renderWithProviders(
+      <ToolConfirmationMessage
+        callId="test-call-id"
+        confirmationDetails={confirmationDetails}
+        config={mockConfig}
+        availableTerminalHeight={30}
+        terminalWidth={80}
+      />,
+    );
+
+    await waitUntilReady();
+
+    const output = lastFrame();
+    expect(output).toContain('Deceptive URL(s) detected');
+    expect(output).toContain('Original: https://еxample.com/');
+    expect(output).toContain(
+      'Actual Host (Punycode): https://xn--xample-2of.com/',
+    );
+    unmount();
+  });
+
+  it('should exclude shell delimiters from extracted URLs in exec type commands', async () => {
+    const confirmationDetails: SerializableConfirmationDetails = {
+      type: 'exec',
+      title: 'Confirm Execution',
+      command: 'curl https://еxample.com;ls',
+      rootCommand: 'curl',
+      rootCommands: ['curl'],
+    };
+
+    const { lastFrame, waitUntilReady, unmount } = renderWithProviders(
+      <ToolConfirmationMessage
+        callId="test-call-id"
+        confirmationDetails={confirmationDetails}
+        config={mockConfig}
+        availableTerminalHeight={30}
+        terminalWidth={80}
+      />,
+    );
+
+    await waitUntilReady();
+
+    const output = lastFrame();
+    expect(output).toContain('Deceptive URL(s) detected');
+    // It should extract "https://еxample.com" and NOT "https://еxample.com;ls"
+    expect(output).toContain('Original: https://еxample.com/');
+    // The command itself still contains 'ls', so we check specifically that 'ls' is not part of the URL line.
+    expect(output).not.toContain('Original: https://еxample.com/;ls');
+    unmount();
+  });
+
+  it('should aggregate multiple deceptive URLs into a single WarningMessage', async () => {
+    const confirmationDetails: SerializableConfirmationDetails = {
+      type: 'info',
+      title: 'Confirm Web Fetch',
+      prompt: 'Fetch both',
+      urls: ['https://еxample.com', 'https://täst.com'],
+    };
+
+    const { lastFrame, waitUntilReady, unmount } = renderWithProviders(
+      <ToolConfirmationMessage
+        callId="test-call-id"
+        confirmationDetails={confirmationDetails}
+        config={mockConfig}
+        availableTerminalHeight={30}
+        terminalWidth={80}
+      />,
+    );
+
+    await waitUntilReady();
+
+    const output = lastFrame();
+    expect(output).toContain('Deceptive URL(s) detected');
+    expect(output).toContain('Original: https://еxample.com/');
+    expect(output).toContain('Original: https://täst.com/');
+    unmount();
+  });
+
   it('should display multiple commands for exec type when provided', async () => {
     const confirmationDetails: SerializableConfirmationDetails = {
       type: 'exec',

packages/cli/src/ui/components/messages/ToolConfirmationMessage.tsx

@@ -37,6 +37,12 @@ import {
 } from '../../textConstants.js';
 import { AskUserDialog } from '../AskUserDialog.js';
 import { ExitPlanModeDialog } from '../ExitPlanModeDialog.js';
+import { WarningMessage } from './WarningMessage.js';
+import {
+  getDeceptiveUrlDetails,
+  toUnicodeUrl,
+  type DeceptiveUrlDetails,
+} from '../../utils/urlSecurityUtils.js';
 
 export interface ToolConfirmationMessageProps {
   callId: string;
@@ -102,6 +108,37 @@ export const ToolConfirmationMessage: React.FC<
     [handleConfirm],
   );
 
+  const deceptiveUrlWarnings = useMemo(() => {
+    const urls: string[] = [];
+    if (confirmationDetails.type === 'info' && confirmationDetails.urls) {
+      urls.push(...confirmationDetails.urls);
+    } else if (confirmationDetails.type === 'exec') {
+      const commands =
+        confirmationDetails.commands && confirmationDetails.commands.length > 0
+          ? confirmationDetails.commands
+          : [confirmationDetails.command];
+      for (const cmd of commands) {
+        const matches = cmd.match(/https?:\/\/[^\s"'`<>;&|()]+/g);
+        if (matches) urls.push(...matches);
+      }
+    }
+
+    const uniqueUrls = Array.from(new Set(urls));
+    return uniqueUrls
+      .map(getDeceptiveUrlDetails)
+      .filter((d): d is DeceptiveUrlDetails => d !== null);
+  }, [confirmationDetails]);
+
+  const deceptiveUrlWarningText = useMemo(() => {
+    if (deceptiveUrlWarnings.length === 0) return null;
+    return `**Warning:** Deceptive URL(s) detected:\n\n${deceptiveUrlWarnings
+      .map(
+        (w) =>
+          `   **Original:** ${w.originalUrl}\n   **Actual Host (Punycode):** ${w.punycodeUrl}`,
+      )
+      .join('\n\n')}`;
+  }, [deceptiveUrlWarnings]);
+
   const getOptions = useCallback(() => {
     const options: Array<RadioSelectItem<ToolConfirmationOutcome>> = [];
 
@@ -262,11 +299,21 @@ export const ToolConfirmationMessage: React.FC<
     return Math.max(availableTerminalHeight - surroundingElementsHeight, 1);
   }, [availableTerminalHeight, getOptions, handlesOwnUI]);
 
-  const { question, bodyContent, options } = useMemo(() => {
+  const { question, bodyContent, options, securityWarnings } = useMemo<{
+    question: string;
+    bodyContent: React.ReactNode;
+    options: Array<RadioSelectItem<ToolConfirmationOutcome>>;
+    securityWarnings: React.ReactNode;
+  }>(() => {
     let bodyContent: React.ReactNode | null = null;
+    let securityWarnings: React.ReactNode | null = null;
     let question = '';
     const options = getOptions();
 
+    if (deceptiveUrlWarningText) {
+      securityWarnings = <WarningMessage text={deceptiveUrlWarningText} />;
+    }
+
     if (confirmationDetails.type === 'ask_user') {
       bodyContent = (
         <AskUserDialog
@@ -281,7 +328,12 @@ export const ToolConfirmationMessage: React.FC<
           availableHeight={availableBodyContentHeight()}
         />
       );
-      return { question: '', bodyContent, options: [] };
+      return {
+        question: '',
+        bodyContent,
+        options: [],
+        securityWarnings: null,
+      };
     }
 
     if (confirmationDetails.type === 'exit_plan_mode') {
@@ -307,7 +359,7 @@ export const ToolConfirmationMessage: React.FC<
           availableHeight={availableBodyContentHeight()}
         />
       );
-      return { question: '', bodyContent, options: [] };
+      return { question: '', bodyContent, options: [], securityWarnings: null };
     }
 
     if (confirmationDetails.type === 'edit') {
@@ -436,10 +488,10 @@ export const ToolConfirmationMessage: React.FC<
           {displayUrls && infoProps.urls && infoProps.urls.length > 0 && (
             <Box flexDirection="column" marginTop={1}>
               <Text color={theme.text.primary}>URLs to fetch:</Text>
-              {infoProps.urls.map((url) => (
+              {infoProps.urls.map((urlString) => (
-                <Text key={url}>
+                <Text key={urlString}>
                   {' '}
-                  - <RenderInline text={url} />
+                  - <RenderInline text={toUnicodeUrl(urlString)} />
                 </Text>
               ))}
             </Box>
@@ -462,13 +514,14 @@ export const ToolConfirmationMessage: React.FC<
       );
     }
 
-    return { question, bodyContent, options };
+    return { question, bodyContent, options, securityWarnings };
   }, [
     confirmationDetails,
     getOptions,
     availableBodyContentHeight,
     terminalWidth,
     handleConfirm,
+    deceptiveUrlWarningText,
   ]);
 
   if (confirmationDetails.type === 'edit') {
@@ -512,6 +565,12 @@ export const ToolConfirmationMessage: React.FC<
             </MaxSizedBox>
           </Box>
 
+          {securityWarnings && (
+            <Box flexShrink={0} marginBottom={1}>
+              {securityWarnings}
+            </Box>
+          )}
+
           <Box marginBottom={1} flexShrink={0}>
             <Text color={theme.text.primary}>{question}</Text>
           </Box>

packages/cli/src/ui/utils/urlSecurityUtils.test.ts

@@ -0,0 +1,65 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect } from 'vitest';
+import { getDeceptiveUrlDetails, toUnicodeUrl } from './urlSecurityUtils.js';
+
+describe('urlSecurityUtils', () => {
+  describe('toUnicodeUrl', () => {
+    it('should convert a Punycode URL string to its Unicode version', () => {
+      expect(toUnicodeUrl('https://xn--tst-qla.com/')).toBe(
+        'https://täst.com/',
+      );
+    });
+
+    it('should convert a URL object to its Unicode version', () => {
+      const urlObj = new URL('https://xn--tst-qla.com/path');
+      expect(toUnicodeUrl(urlObj)).toBe('https://täst.com/path');
+    });
+
+    it('should handle complex URLs with credentials and ports', () => {
+      const complexUrl = 'https://user:pass@xn--tst-qla.com:8080/path?q=1#hash';
+      expect(toUnicodeUrl(complexUrl)).toBe(
+        'https://user:pass@täst.com:8080/path?q=1#hash',
+      );
+    });
+
+    it('should correctly reconstruct the URL even if the hostname appears in the path', () => {
+      const urlWithHostnameInPath =
+        'https://xn--tst-qla.com/some/path/xn--tst-qla.com/index.html';
+      expect(toUnicodeUrl(urlWithHostnameInPath)).toBe(
+        'https://täst.com/some/path/xn--tst-qla.com/index.html',
+      );
+    });
+
+    it('should return the original string if URL parsing fails', () => {
+      expect(toUnicodeUrl('not a url')).toBe('not a url');
+    });
+
+    it('should return the original string for already safe URLs', () => {
+      expect(toUnicodeUrl('https://google.com/')).toBe('https://google.com/');
+    });
+  });
+
+  describe('getDeceptiveUrlDetails', () => {
+    it('should return full details for a deceptive URL', () => {
+      const details = getDeceptiveUrlDetails('https://еxample.com');
+      expect(details).not.toBeNull();
+      expect(details?.originalUrl).toBe('https://еxample.com/');
+      expect(details?.punycodeUrl).toBe('https://xn--xample-2of.com/');
+    });
+
+    it('should return null for safe URLs', () => {
+      expect(getDeceptiveUrlDetails('https://google.com')).toBeNull();
+    });
+
+    it('should handle already Punycoded hostnames', () => {
+      const details = getDeceptiveUrlDetails('https://xn--tst-qla.com');
+      expect(details).not.toBeNull();
+      expect(details?.originalUrl).toBe('https://täst.com/');
+    });
+  });
+});

packages/cli/src/ui/utils/urlSecurityUtils.ts

@@ -0,0 +1,90 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import url from 'node:url';
+
+/**
+ * Details about a deceptive URL.
+ */
+export interface DeceptiveUrlDetails {
+  /** The Unicode version of the visually deceptive URL. */
+  originalUrl: string;
+  /** The ASCII-safe Punycode version of the URL. */
+  punycodeUrl: string;
+}
+
+/**
+ * Whether a hostname contains non-ASCII or Punycode markers.
+ *
+ * @param hostname The hostname to check.
+ * @returns true if deceptive markers are found, false otherwise.
+ */
+function containsDeceptiveMarkers(hostname: string): boolean {
+  return (
+    // eslint-disable-next-line no-control-regex
+    hostname.toLowerCase().includes('xn--') || /[^\x00-\x7F]/.test(hostname)
+  );
+}
+
+/**
+ * Converts a URL (string or object) to its visually deceptive Unicode version.
+ *
+ * This function manually reconstructs the URL to bypass the automatic Punycode
+ * conversion performed by the WHATWG URL class when setting the hostname.
+ *
+ * @param urlInput The URL string or URL object to convert.
+ * @returns The reconstructed URL string with the hostname in Unicode.
+ */
+export function toUnicodeUrl(urlInput: string | URL): string {
+  try {
+    const urlObj = typeof urlInput === 'string' ? new URL(urlInput) : urlInput;
+    const punycodeHost = urlObj.hostname;
+    const unicodeHost = url.domainToUnicode(punycodeHost);
+
+    // Reconstruct the URL manually because the WHATWG URL class automatically
+    // Punycodes the hostname if we try to set it.
+    const protocol = urlObj.protocol + '//';
+    const credentials = urlObj.username
+      ? `${urlObj.username}${urlObj.password ? ':' + urlObj.password : ''}@`
+      : '';
+    const port = urlObj.port ? ':' + urlObj.port : '';
+
+    return `${protocol}${credentials}${unicodeHost}${port}${urlObj.pathname}${urlObj.search}${urlObj.hash}`;
+  } catch {
+    return typeof urlInput === 'string' ? urlInput : urlInput.href;
+  }
+}
+
+/**
+ * Extracts deceptive URL details if a URL hostname contains non-ASCII characters
+ * or is already in Punycode.
+ *
+ * @param urlString The URL string to check.
+ * @returns DeceptiveUrlDetails if a potential deceptive URL is detected, otherwise null.
+ */
+export function getDeceptiveUrlDetails(
+  urlString: string,
+): DeceptiveUrlDetails | null {
+  try {
+    if (!urlString.includes('://')) {
+      return null;
+    }
+
+    const urlObj = new URL(urlString);
+
+    if (!containsDeceptiveMarkers(urlObj.hostname)) {
+      return null;
+    }
+
+    return {
+      originalUrl: toUnicodeUrl(urlObj),
+      punycodeUrl: urlObj.href,
+    };
+  } catch {
+    // If URL parsing fails, it's not a valid URL we can safely analyze.
+    return null;
+  }
+}