lib/links.js

@@ -0,0 +1,28 @@
+module.exports = {
+  serveLinkWarningPage: function (req, res) {
+    let targetURL = typeof req.query.url === 'string' ? req.query.url : ''
+    let noteURL = typeof req.query.note === 'string' ? req.query.note : ''
+    if (noteURL !== '' && !/^[\w-]+$/.test(noteURL)) {
+      noteURL = ''
+    }
+    let valid = false
+    try {
+      targetURL = decodeURIComponent(targetURL)
+      const parsed = new URL(targetURL)
+      valid = ['http:', 'https:'].includes(parsed.protocol)
+      targetURL = parsed.href
+    } catch (err) {
+      valid = false
+    }
+    res.set({
+      'Cache-Control': 'no-store'
+    })
+    res.render('link.ejs', {
+      title: 'External link',
+      valid,
+      noteURL,
+      targetURL,
+      opengraph: []
+    })
+  }
+}

lib/web/baseRouter.js

@@ -8,6 +8,8 @@ const baseRouter = module.exports = Router()
 
 const errors = require('../errors')
 
+const links = require('../links')
+
 // get index
 baseRouter.get('/', response.showIndex)
 // get 403 forbidden
@@ -22,3 +24,5 @@ baseRouter.get('/404', function (req, res) {
 baseRouter.get('/500', function (req, res) {
   errors.errorInternalError(res)
 })
+// get external link warning page
+baseRouter.get('/_link', links.serveLinkWarningPage)

locales/de.json

@@ -126,5 +126,13 @@
     "Protected - Only owner can edit (forbid guests)": "Geschützt - Nur Besitzer kann bearbeiten (Gäste verboten)",
     "Private - Only owner can view & edit": "Privat - Nur Besitzer kann anschauen & bearbeiten",
     "changed": "verändert",
-    "created": "erstellt"
+    "created": "erstellt",
+    "External link": "Externer Link",
+    "You've clicked a link that points to an external page.": "Es wurde ein Link zu einer externen Seite angeklickt.",
+    "The content of that page is unrelated to HedgeDoc. Do not enter your HedgeDoc credentials there.": "Der Inhalt dieser Seite ist unabhängig von HedgeDoc. Dort keine HedgeDoc-Zugangsdaten eingeben.",
+    "Do you want to continue?": "Fortfahren?",
+    "Continue to external page": "Weiter zur externen Seite",
+    "Back to your note": "Zurück zur Notiz",
+    "Invalid link": "Ungültiger Link",
+    "The provided link is not a valid URL.": "Die angegebene URL ist nicht gültig."
 }

locales/en.json

@@ -126,5 +126,13 @@
     "Protected - Only owner can edit (forbid guests)": "Protected - Only owner can edit (forbid guests)",
     "Private - Only owner can view & edit": "Private - Only owner can view & edit",
     "changed": "changed",
-    "created": "created"
+    "created": "created",
+    "You've clicked a link that points to an external page.": "You've clicked a link that points to an external page.",
+    "External link": "External link",
+    "Invalid link": "Invalid link",
+    "Do you want to continue?": "Do you want to continue?",
+    "Continue to external page": "Continue to external page",
+    "Back to your note": "Back to your note",
+    "The provided link is not a valid URL.": "The provided link is not a valid URL.",
+    "The content of that page is unrelated to HedgeDoc. Do not enter your HedgeDoc credentials there.": "The content of that page is unrelated to HedgeDoc. Do not enter your HedgeDoc credentials there."
 }

public/docs/release-notes.md

@@ -1,5 +1,11 @@
 # Release Notes
 
+## <i class="fa fa-tag"></i> 1.x <i class="fa fa-calendar-o"></i> UNRELEASED
+
+### Enhancements
+
+- Added a warning page when clicking external links
+
 ## <i class="fa fa-tag"></i> 1.10.8 <i class="fa fa-calendar-o"></i> 2026-04-15
 
 ### Bugfixes

public/js/extra.js

@@ -557,10 +557,6 @@ export function postProcess (code) {
     html = html.replace(/@import url\(([^)]*)\);?/gi, '')
     $(value).html(html)
   })
-  // link should open in new window or tab
-  // also add noopener to prevent clickjacking
-  // See details: https://mathiasbynens.github.io/rel-noopener/
-  result.find('a:not([href^="#"]):not([target])').attr('target', '_blank').attr('rel', 'noopener')
 
   // If it's hashtag link then make it base uri independent
   result.find('a[href^="#"]').each((index, linkTag) => {
@@ -568,6 +564,7 @@ export function postProcess (code) {
     currentLocation.hash = linkTag.hash
     linkTag.href = currentLocation.toString()
   })
+  rewriteExternalLinks(result)
 
   // update continue line numbers
   const linenumberdivs = result.find('.gutter.linenumber').toArray()
@@ -593,6 +590,30 @@ export function postProcess (code) {
 }
 window.postProcess = postProcess
 
+// rewrite external links to go through the /_link warning page
+export function rewriteExternalLinks (view) {
+  view.find('a[href]').each((index, linkTag) => {
+    const anchor = $(linkTag)
+    const href = anchor.attr('href')
+    if (!href || href.startsWith('#')) {
+      return
+    }
+    let parsed
+    try {
+      parsed = new URL(href)
+    } catch (err) {
+      return
+    }
+    // only rewrite links that have an absolute http(s) URL on a different origin
+    if (!['http:', 'https:'].includes(parsed.protocol) || parsed.origin === window.location.origin) {
+      return
+    }
+    const noteURL = window.location.pathname.split('/').pop()
+    anchor.attr('href', `${window.location.origin}/_link?url=${encodeURIComponent(parsed.href)}&note=${noteURL}`)
+  })
+}
+window.rewriteExternalLinks = rewriteExternalLinks
+
 const domevents = Object.getOwnPropertyNames(document).concat(Object.getOwnPropertyNames(Object.getPrototypeOf(Object.getPrototypeOf(document)))).concat(Object.getOwnPropertyNames(Object.getPrototypeOf(window))).filter(function (i) {
   return !i.indexOf('on') && (document[i] === null || typeof document[i] === 'function')
 }).filter(function (elem, pos, self) {

public/js/index.js

@@ -55,6 +55,7 @@ import {
   renderTOC,
   renderTags,
   renderTitle,
+  rewriteExternalLinks,
   scrollToHash,
   smoothHashScroll,
   updateLastChange,
@@ -3498,6 +3499,7 @@ function updateViewInner () {
   }
   removeDOMEvents(ui.area.markdown)
   finishView(ui.area.markdown)
+  rewriteExternalLinks(ui.area.markdown)
   autoLinkify(ui.area.markdown)
   deduplicatedHeaderId(ui.area.markdown)
   renderTOC(ui.area.markdown)

public/views/link.ejs

@@ -0,0 +1,41 @@
+<!DOCTYPE html>
+<html lang="en">
+
+<head>
+    <%- include('hedgedoc/head') %>
+    <link rel="stylesheet" href="<%- serverURL %>/css/center.css">
+</head>
+
+<body>
+    <%- include('hedgedoc/header') %>
+    <div class="container-fluid text-center">
+        <div class="vertical-center-row">
+            <h1>
+                <% if (valid) { %>
+                <%= __('External link') %>
+                <% } else { %>
+                <%= __('Invalid link') %>
+                <% } %>
+            </h1>
+            <p>
+              <%= __('You\'ve clicked a link that points to an external page.') %>
+              <br>
+              <%= __('The content of that page is unrelated to HedgeDoc. Do not enter your HedgeDoc credentials there.') %>
+            </p>
+            <% if (valid) { %>
+            <p><code class="text-break"><%- targetURL %></code></p>
+            <p><%= __('Do you want to continue?') %></p>
+            <p>
+                <a class="btn btn-primary" href="<%- targetURL %>"><%= __('Continue to external page') %></a>
+                <a class="btn btn-default" href="<%- serverURL %>/<%- noteURL %>"><%= __('Back to your note') %></a>
+            </p>
+            <% } else { %>
+            <p class="text-danger"><strong><%= __('The provided link is not a valid URL.') %></strong></p>
+            <p>
+                <a class="btn btn-default" href="<%- serverURL %>/<%- noteURL %>"><%= __('Back to your note') %></a>
+            </p>
+            <% } %>
+        </div>
+    </div>
+</body>
+</html>