diff --git a/packages/preview/package.json b/packages/preview/package.json
index 491c1b82a679e..d5f2081d490f6 100644
--- a/packages/preview/package.json
+++ b/packages/preview/package.json
@@ -10,9 +10,11 @@
     "@types/highlight.js": "^9.12.2",
     "@types/markdown-it": "*",
     "@types/markdown-it-anchor": "^4.0.1",
+    "@types/dompurify": "^2.0.2",
     "highlight.js": "^9.12.0",
     "markdown-it": "^8.4.0",
-    "markdown-it-anchor": "~5.0.0"
+    "markdown-it-anchor": "~5.0.0",
+    "dompurify": "^2.0.11"
   },
   "publishConfig": {
     "access": "public"
diff --git a/packages/preview/src/browser/markdown/markdown-preview-handler.spec.ts b/packages/preview/src/browser/markdown/markdown-preview-handler.spec.ts
index e556646ed7494..8605bcb0d4fcf 100644
--- a/packages/preview/src/browser/markdown/markdown-preview-handler.spec.ts
+++ b/packages/preview/src/browser/markdown/markdown-preview-handler.spec.ts
@@ -130,11 +130,11 @@ See [here](https://github.com/eclipse-theia/theia).
 `;
 
 const exampleHtml1 = //
-    `<h1 id="theia---preview-extension" class="line" data-line="0">Theia - Preview Extension</h1>
-<p class="line" data-line="1">Shows a preview of supported resources.
+    `<h1 data-line="0" class="line" id="theia---preview-extension">Theia - Preview Extension</h1>
+<p data-line="1" class="line">Shows a preview of supported resources.
 See <a href="https://github.com/eclipse-theia/theia">here</a>.</p>
-<h2 id="license" class="line" data-line="4">License</h2>
-<p class="line" data-line="5"><a href="https://github.com/eclipse-theia/theia/blob/master/LICENSE">Apache-2.0</a></p>
+<h2 data-line="4" class="line" id="license">License</h2>
+<p data-line="5" class="line"><a href="https://github.com/eclipse-theia/theia/blob/master/LICENSE">Apache-2.0</a></p>
 `;
 
 const exampleMarkdown2 = //
@@ -143,8 +143,8 @@ const exampleMarkdown2 = //
 `;
 
 const exampleHtml2 = //
-    `<h1 id="heading" class="line" data-line="0">Heading</h1>
-<p class="line" data-line="1"><img src="endpoint/workspace/subfolder/image.png" alt="alternativetext"></p>
+    `<h1 data-line="0" class="line" id="heading">Heading</h1>
+<p data-line="1" class="line"><img alt="alternativetext" src="endpoint/workspace/subfolder/image.png"></p>
 `;
 
 const exampleMarkdown3 = //
@@ -156,10 +156,10 @@ const exampleMarkdown3 = //
 `;
 
 const exampleHtml3 = //
-    `<h1 id="block-html-image" class="line" data-line="0">Block HTML Image</h1>
-<img src="endpoint/workspace/subfolder/image1.png" alt="tada">
-<h1 id="block-html-image-2" class="line" data-line="3">Block HTML Image</h1>
-<img src="endpoint/workspace/subfolder/image3.png" alt="tada">
+    `<h1 data-line="0" class="line" id="block-html-image">Block HTML Image</h1>
+<img alt="tada" src="endpoint/workspace/subfolder/image1.png">
+<h1 data-line="3" class="line" id="block-html-image-2">Block HTML Image</h1>
+<img alt="tada" src="endpoint/workspace/subfolder/image3.png">
 `;
 
 const exampleMarkdown4 = //
@@ -168,8 +168,8 @@ text in paragraph <img src="subfolder/image2.png" alt="tada"/>
 `;
 
 const exampleHtml4 = //
-    `<h1 id="inlined-html-image" class="line" data-line="0">Inlined HTML Image</h1>
-<p class="line" data-line="1">text in paragraph <img src="endpoint/workspace/subfolder/image2.png" alt="tada"></p>
+    `<h1 data-line="0" class="line" id="inlined-html-image">Inlined HTML Image</h1>
+<p data-line="1" class="line">text in paragraph <img alt="tada" src="endpoint/workspace/subfolder/image2.png"></p>
 `;
 
 const exampleMarkdown5 = //
@@ -184,12 +184,12 @@ word  <p>
 `;
 
 const exampleHtml5 = //
-    `<h1 id="multiple-html-images-nested-in-blocks" class="line" data-line="0">Multiple HTML Images nested in blocks</h1>
-<p class="line" data-line="1">word  </p><p>
-<img src="endpoint/workspace/subfolder/image2.png" alt="tada"></p>
+    `<h1 data-line="0" class="line" id="multiple-html-images-nested-in-blocks">Multiple HTML Images nested in blocks</h1>
+<p data-line="1" class="line">word  </p><p>
+<img alt="tada" src="endpoint/workspace/subfolder/image2.png"></p>
 <p></p>
 <p>
-<img src="endpoint/workspace/subfolder/image2.png" alt="tada">
+<img alt="tada" src="endpoint/workspace/subfolder/image2.png">
 </p>
 `;
 
diff --git a/packages/preview/src/browser/markdown/markdown-preview-handler.ts b/packages/preview/src/browser/markdown/markdown-preview-handler.ts
index ea117928cf669..e8907d169e55b 100644
--- a/packages/preview/src/browser/markdown/markdown-preview-handler.ts
+++ b/packages/preview/src/browser/markdown/markdown-preview-handler.ts
@@ -23,6 +23,7 @@ import { Path } from '@theia/core/lib/common/path';
 import * as hljs from 'highlight.js';
 import * as markdownit from 'markdown-it';
 import * as anchor from 'markdown-it-anchor';
+import * as DOMPurify from 'dompurify';
 import { PreviewUri } from '../preview-uri';
 import { PreviewHandler, RenderContentParams } from '../preview-handler';
 import { PreviewOpenerOptions } from '../preview-contribution';
@@ -51,9 +52,10 @@ export class MarkdownPreviewHandler implements PreviewHandler {
     renderContent(params: RenderContentParams): HTMLElement {
         const content = params.content;
         const renderedContent = this.getEngine().render(content, params);
+        const sanitizedContent = DOMPurify.sanitize(renderedContent);
         const contentElement = document.createElement('div');
         contentElement.classList.add(this.contentClass);
-        contentElement.innerHTML = renderedContent;
+        contentElement.innerHTML = sanitizedContent;
         this.addLinkClickedListener(contentElement, params);
         return contentElement;
     }
diff --git a/yarn.lock b/yarn.lock
index dce9900cd0159..a0cefbd5d2315 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1127,6 +1127,13 @@
   resolved "https://registry.yarnpkg.com/@types/domhandler/-/domhandler-2.4.1.tgz#7b3b347f7762180fbcb1ece1ce3dd0ebbb8c64cf"
   integrity sha512-cfBw6q6tT5sa1gSPFSRKzF/xxYrrmeiut7E0TxNBObiLSBTuFEHibcfEe3waQPEDbqBsq+ql/TOniw65EyDFMA==
 
+"@types/dompurify@^2.0.2":
+  version "2.0.2"
+  resolved "https://registry.yarnpkg.com/@types/dompurify/-/dompurify-2.0.2.tgz#94b5c05dc9b8a682a0abb4a8d6f0b82df61baeac"
+  integrity sha512-WHoQQTziRHm5/Fw/KsUKyh2V+wd3k2QUpJyjUXo8K7d9kMJ5i5wQnGDkO4URkwulhY2HuM/gbX25nSooi6+wUA==
+  dependencies:
+    "@types/trusted-types" "*"
+
 "@types/domutils@*":
   version "1.7.2"
   resolved "https://registry.yarnpkg.com/@types/domutils/-/domutils-1.7.2.tgz#89422e579c165994ad5c09ce90325da596cc105d"
@@ -1471,6 +1478,11 @@
   resolved "https://registry.yarnpkg.com/@types/tough-cookie/-/tough-cookie-2.3.6.tgz#c880579e087d7a0db13777ff8af689f4ffc7b0d5"
   integrity sha512-wHNBMnkoEBiRAd3s8KTKwIuO9biFtTf0LehITzBhSco+HQI0xkXZbLOD55SW3Aqw3oUkHstkm5SPv58yaAdFPQ==
 
+"@types/trusted-types@*":
+  version "1.0.4"
+  resolved "https://registry.yarnpkg.com/@types/trusted-types/-/trusted-types-1.0.4.tgz#922d092c84a776a59acb0bd6785fd82b59b9bad5"
+  integrity sha512-6jtHrHpmiXOXoJ31Cg9R+iEVwuEKPf0XHwFUI93eEPXx492/J2JHyafkleKE2EYzZprayk9FSjTyK1GDqcwDng==
+
 "@types/uglify-js@*":
   version "3.0.4"
   resolved "https://registry.yarnpkg.com/@types/uglify-js/-/uglify-js-3.0.4.tgz#96beae23df6f561862a830b4288a49e86baac082"
@@ -4854,6 +4866,11 @@ domhandler@^3.0.0:
   dependencies:
     domelementtype "^2.0.1"
 
+dompurify@^2.0.11:
+  version "2.0.11"
+  resolved "https://registry.yarnpkg.com/dompurify/-/dompurify-2.0.11.tgz#cd47935774230c5e478b183a572e726300b3891d"
+  integrity sha512-qVoGPjIW9IqxRij7klDQQ2j6nSe4UNWANBhZNLnsS7ScTtLb+3YdxkRY8brNTpkUiTtcXsCJO+jS0UCDfenLuA==
+
 domutils@^2.0.0:
   version "2.0.0"
   resolved "https://registry.yarnpkg.com/domutils/-/domutils-2.0.0.tgz#15b8278e37bfa8468d157478c58c367718133c08"