fix(previews): no genuine preview card for a site a deceptive link only pretends to be (#286)

Previews are built from the plain body, clicks follow formatted_body's
hrefs, and a sender controls both: text "https://paypal.com" linked to
evil.example showed a real PayPal card. Drop body URLs whose site is
only claimed by the visible text of a mismatched link (linkSafety).

Fixes #286

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/components/message/MsgTypeRenderers.tsx

@@ -40,6 +40,7 @@ import { parseGeoUri, scaleYDimension } from '../../utils/common';
 import { formatAccuracy } from '../../utils/geoShare';
 import { Attachment, AttachmentBox, AttachmentContent, AttachmentHeader } from './attachment';
 import { FileHeader, FileDownloadButton } from './FileHeader';
+import { previewUrlsFor } from '../../utils/linkSafety';
 
 // ≈ 20 lines; in rem so a larger font setting doesn't show fewer lines (Gitea #343).
 const COLLAPSE_MAX_HEIGHT_REM = 20;
@@ -343,7 +344,13 @@ export function MText({
   if (typeof body !== 'string') return <BrokenContent />;
   const trimmedBody = trimReplyFromBody(body);
   const urlsMatch = renderUrlsPreview && trimmedBody.match(URL_REG);
-  const urls = urlsMatch ? [...new Set(urlsMatch)] : undefined;
+  // [Gitea #286] no genuine card for a site a deceptive link only pretends to be
+  const urls = urlsMatch
+    ? previewUrlsFor(
+        [...new Set(urlsMatch)],
+        typeof customBody === 'string' ? customBody : undefined,
+      )
+    : undefined;
 
   return (
     <>
@@ -401,7 +408,13 @@ export function MEmote({
   if (typeof body !== 'string') return <BrokenContent />;
   const trimmedBody = trimReplyFromBody(body);
   const urlsMatch = renderUrlsPreview && trimmedBody.match(URL_REG);
-  const urls = urlsMatch ? [...new Set(urlsMatch)] : undefined;
+  // [Gitea #286] no genuine card for a site a deceptive link only pretends to be
+  const urls = urlsMatch
+    ? previewUrlsFor(
+        [...new Set(urlsMatch)],
+        typeof customBody === 'string' ? customBody : undefined,
+      )
+    : undefined;
 
   return (
     <>
@@ -458,7 +471,13 @@ export function MNotice({
   if (typeof body !== 'string') return <BrokenContent />;
   const trimmedBody = trimReplyFromBody(body);
   const urlsMatch = renderUrlsPreview && trimmedBody.match(URL_REG);
-  const urls = urlsMatch ? [...new Set(urlsMatch)] : undefined;
+  // [Gitea #286] no genuine card for a site a deceptive link only pretends to be
+  const urls = urlsMatch
+    ? previewUrlsFor(
+        [...new Set(urlsMatch)],
+        typeof customBody === 'string' ? customBody : undefined,
+      )
+    : undefined;
 
   return (
     <>

src/app/hooks/useMessageTranslation.ts

@@ -12,8 +12,7 @@ import {
   markAutoTranslateTried,
 } from '../state/translation';
 import { chromeTranslationEngine as engine } from '../utils/translation/chromeEngine';
-import { sameLanguage, translateSkipMessage } from '../utils/translation/langUtils';
-import { toastQueueAtom } from '../state/toast';
+import { sameLanguage } from '../utils/translation/langUtils';
 
 export type MsgTranslationStatus =
   | 'idle' // not translating (original shown)
@@ -53,7 +52,6 @@ export const useMessageTranslation = (eventId: string, text: string): MsgTransla
   // Write-only: reading the whole cache array here (via useAtom) would
   // resubscribe this message to every other message's writes. [Gitea #39]
   const setCache = useSetAtom(translationCacheAtom);
-  const setToast = useSetAtom(toastQueueAtom);
 
   // The key includes a fingerprint of `text`, so an edit (same event id, new
   // body) misses the old entry and re-translates instead of showing stale
@@ -126,16 +124,6 @@ export const useMessageTranslation = (eventId: string, text: string): MsgTransla
         if (!from || sameLanguage(from, targetLang)) {
           setStatus('skipped');
           setActive(false);
-          // [Gitea #287] Say why nothing happened instead of silently undoing
-          // the click (no chip shows once translation is switched back off).
-          setToast({
-            id: `translate-skipped-${eventId}-${Date.now()}`,
-            displayName: 'Translate',
-            body: translateSkipMessage(from, targetLang),
-            roomName: '',
-            roomId: '',
-            onClick: () => undefined,
-          });
           return;
         }
         setFromLang(from);
@@ -166,7 +154,7 @@ export const useMessageTranslation = (eventId: string, text: string): MsgTransla
       // Invalidate this run's writes if inputs change / unmount.
       runIdRef.current += 1;
     };
-  }, [active, cached, supported, text, targetLang, key, setActive, setCache, setToast, eventId]);
+  }, [active, cached, supported, text, targetLang, key, setActive, setCache]);
 
   // When switched off, drop back to idle (keep the cached translation around so
   // toggling back on is instant).

src/app/utils/linkSafety.test.ts

@@ -1,6 +1,6 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
-import { analyzeLink, hostFromText, registrableDomain } from './linkSafety';
+import { analyzeLink, hostFromText, previewUrlsFor, registrableDomain } from './linkSafety';
 
 test('visible text that names another site is a mismatch', () => {
   const r = analyzeLink('https://matrix.lotusguild.org/login', 'https://evil.example/login');
@@ -73,3 +73,25 @@ test('shared hosting suffixes are separate sites (#335)', () => {
   );
   assert.equal(registrableDomain('news.bbc.co.uk'), 'bbc.co.uk');
 });
+
+test('previewUrlsFor: no preview for a site a deceptive link only claims (#286)', () => {
+  const urls = ['https://paypal.com'];
+  assert.deepEqual(
+    previewUrlsFor(urls, '<a href="https://evil.example/login">https://paypal.com</a>'),
+    [],
+  );
+  // An honest link keeps its preview.
+  assert.deepEqual(
+    previewUrlsFor(urls, '<a href="https://www.paypal.com/x">https://paypal.com</a>'),
+    urls,
+  );
+  assert.deepEqual(previewUrlsFor(urls, undefined), urls);
+  // Other links in the message keep theirs.
+  assert.deepEqual(
+    previewUrlsFor(
+      ['https://paypal.com', 'https://lotusguild.org'],
+      'see <a href="https://evil.example">paypal.com</a> and https://lotusguild.org',
+    ),
+    ['https://lotusguild.org'],
+  );
+});

src/app/utils/linkSafety.ts

@@ -221,3 +221,37 @@ export const analyzeLink = (text: string, href: string): LinkSafety | null => {
   const other = shown.find((h) => registrableDomain(h) !== realSite);
   return { mismatch: other !== undefined, shownHost: other ?? shown[0], realHost, punycode };
 };
+
+const ANCHOR_REG = /<a\s[^>]*href\s*=\s*(["'])(.*?)\1[^>]*>([\s\S]*?)<\/a>/gi;
+const decodeEntities = (s: string): string =>
+  s
+    .replace(/<[^>]+>/g, '')
+    .replace(/&quot;/g, '"')
+    .replace(/&#39;/g, "'")
+    .replace(/&lt;/g, '<')
+    .replace(/&gt;/g, '>')
+    .replace(/&amp;/g, '&');
+
+/**
+ * [Gitea #286] The URLs to build link previews for. Previews come from the
+ * plain `body`, but clicks follow `formatted_body`'s hrefs, and a sender
+ * controls both: text reading "https://paypal.com" linked to evil.example got
+ * a genuine PayPal card. Drop any body URL whose site is only *claimed* by a
+ * deceptive link's text.
+ */
+export const previewUrlsFor = (urls: string[], formattedBody: string | undefined): string[] => {
+  if (!formattedBody || urls.length === 0) return urls;
+  const claimed = new Set<string>();
+  Array.from(formattedBody.matchAll(ANCHOR_REG)).forEach((m) => {
+    const safety = analyzeLink(decodeEntities(m[3]), decodeEntities(m[2]));
+    if (safety?.mismatch && safety.shownHost) claimed.add(registrableDomain(safety.shownHost));
+  });
+  if (claimed.size === 0) return urls;
+  return urls.filter((u) => {
+    try {
+      return !claimed.has(registrableDomain(new URL(u).hostname));
+    } catch {
+      return true;
+    }
+  });
+};

src/app/utils/translation/langUtils.ts

@@ -85,9 +85,3 @@ export function languageName(code: string, uiLocale = 'en'): string {
 export function isSupportedTargetLang(code: string): boolean {
   return CURATED_NAME.has(normalizeLang(code));
 }
-
-/** Pure: why a manual Translate did nothing (#287). */
-export const translateSkipMessage = (from: string | undefined, targetLang: string): string =>
-  from
-    ? `This message is already in ${languageName(targetLang) || targetLang}.`
-    : "Couldn't tell what language this message is in, so it wasn't translated.";

src/app/utils/translation/translateSkip.test.ts

@@ -1,8 +0,0 @@
-import { test } from 'node:test';
-import assert from 'node:assert/strict';
-import { translateSkipMessage } from './langUtils';
-
-test('translateSkipMessage explains a Translate that did nothing (#287)', () => {
-  assert.equal(translateSkipMessage('en', 'en'), 'This message is already in English.');
-  assert.match(translateSkipMessage(undefined, 'en'), /^Couldn't tell what language/);
-});