diff --git a/services/web/frontend/js/features/source-editor/components/command-tooltip/href-tooltip.tsx b/services/web/frontend/js/features/source-editor/components/command-tooltip/href-tooltip.tsx
index a0d681d9cb..2f9a4333cd 100644
--- a/services/web/frontend/js/features/source-editor/components/command-tooltip/href-tooltip.tsx
+++ b/services/web/frontend/js/features/source-editor/components/command-tooltip/href-tooltip.tsx
@@ -17,6 +17,7 @@ import {
 import { Button, ControlLabel, FormControl, FormGroup } from 'react-bootstrap'
 import Icon from '../../../../shared/components/icon'
 import { EditorState } from '@codemirror/state'
+import { openURL } from '@/features/source-editor/utils/url'
 
 export const HrefTooltipContent: FC = () => {
   const state = useCodeMirrorStateContext()
@@ -108,7 +109,7 @@ export const HrefTooltipContent: FC = () => {
         className="ol-cm-command-tooltip-link"
         onClick={() => {
           // TODO: unescape content
-          window.open(url, '_blank')
+          openURL(url)
         }}
       >
         <Icon type="external-link" fw />
diff --git a/services/web/frontend/js/features/source-editor/components/command-tooltip/url-tooltip.tsx b/services/web/frontend/js/features/source-editor/components/command-tooltip/url-tooltip.tsx
index c51b497de0..632d71dd03 100644
--- a/services/web/frontend/js/features/source-editor/components/command-tooltip/url-tooltip.tsx
+++ b/services/web/frontend/js/features/source-editor/components/command-tooltip/url-tooltip.tsx
@@ -9,6 +9,7 @@ import {
 } from '../../lezer-latex/latex.terms.mjs'
 import Icon from '../../../../shared/components/icon'
 import { EditorState } from '@codemirror/state'
+import { openURL } from '@/features/source-editor/utils/url'
 
 export const UrlTooltipContent: FC = () => {
   const { t } = useTranslation()
@@ -23,7 +24,7 @@ export const UrlTooltipContent: FC = () => {
         onClick={() => {
           const url = readUrl(state)
           if (url) {
-            window.open(url, '_blank')
+            openURL(url)
           }
         }}
       >
diff --git a/services/web/frontend/js/features/source-editor/utils/url.ts b/services/web/frontend/js/features/source-editor/utils/url.ts
new file mode 100644
index 0000000000..8bfc9bdeab
--- /dev/null
+++ b/services/web/frontend/js/features/source-editor/utils/url.ts
@@ -0,0 +1,11 @@
+const ALLOWED_PROTOCOLS = ['https:', 'http:']
+
+export const openURL = (content: string) => {
+  const url = new URL(content, document.location.href)
+
+  if (!ALLOWED_PROTOCOLS.includes(url.protocol)) {
+    throw new Error(`Not opening URL with protocol ${url.protocol}`)
+  }
+
+  window.open(url, '_blank')
+}
diff --git a/services/web/test/frontend/features/source-editor/components/codemirror-editor-visual-command-tooltip.spec.tsx b/services/web/test/frontend/features/source-editor/components/codemirror-editor-visual-command-tooltip.spec.tsx
index 837f90a64a..d46b522a11 100644
--- a/services/web/test/frontend/features/source-editor/components/codemirror-editor-visual-command-tooltip.spec.tsx
+++ b/services/web/test/frontend/features/source-editor/components/codemirror-editor-visual-command-tooltip.spec.tsx
@@ -54,8 +54,8 @@ describe('<CodeMirrorEditor/> command tooltip in Visual mode', function () {
     // open the link
     cy.findByRole('button', { name: 'Go to page' }).click()
     cy.get('@window-open').should(
-      'have.been.calledOnceWithExactly',
-      'https://example.com',
+      'have.been.calledWithMatch',
+      Cypress.sinon.match.has('href', 'https://example.com/'),
       '_blank'
     )
 
@@ -112,8 +112,8 @@ describe('<CodeMirrorEditor/> command tooltip in Visual mode', function () {
     // open the link
     cy.findByRole('button', { name: 'Go to page' }).click()
     cy.get('@window-open').should(
-      'have.been.calledOnceWithExactly',
-      'https://example.com',
+      'have.been.calledWithMatch',
+      Cypress.sinon.match.has('href', 'https://example.com/'),
       '_blank'
     )
   })
diff --git a/services/web/test/frontend/features/source-editor/components/codemirror-editor-visual-tooltips.spec.tsx b/services/web/test/frontend/features/source-editor/components/codemirror-editor-visual-tooltips.spec.tsx
index c6e28f9eee..106a80ba18 100644
--- a/services/web/test/frontend/features/source-editor/components/codemirror-editor-visual-tooltips.spec.tsx
+++ b/services/web/test/frontend/features/source-editor/components/codemirror-editor-visual-tooltips.spec.tsx
@@ -42,8 +42,8 @@ describe('<CodeMirrorEditor/> tooltips in Visual mode', function () {
       })
       cy.findByRole('button', { name: 'Go to page' }).click()
       cy.get('@open-window').should(
-        'have.been.calledOnceWithExactly',
-        'https://example.com/foo',
+        'have.been.calledWithMatch',
+        Cypress.sinon.match.has('href', 'https://example.com/foo'),
         '_blank'
       )
       cy.findByRole('button', { name: 'Remove link' }).click()
@@ -62,8 +62,8 @@ describe('<CodeMirrorEditor/> tooltips in Visual mode', function () {
       })
       cy.findByRole('button', { name: 'Go to page' }).click()
       cy.get('@open-window').should(
-        'have.been.calledOnceWithExactly',
-        'https://example.com',
+        'have.been.calledWithMatch',
+        Cypress.sinon.match.has('href', 'https://example.com/'),
         '_blank'
       )
     })