diff --git a/frontend/package-lock.json b/frontend/package-lock.json
index d5d8550d..0eb4c188 100644
--- a/frontend/package-lock.json
+++ b/frontend/package-lock.json
@@ -9,8 +9,10 @@
       "version": "0.0.0",
       "dependencies": {
         "@reduxjs/toolkit": "^2.11.2",
+        "@types/dompurify": "^3.0.5",
         "@xyflow/react": "^12.8.3",
         "antd": "^5.27.0",
+        "dompurify": "^3.4.10",
         "i18next": "^25.8.0",
         "jssha": "^3.3.1",
         "jszip": "^3.10.1",
@@ -2416,6 +2418,15 @@
         "@types/ms": "*"
       }
     },
+    "node_modules/@types/dompurify": {
+      "version": "3.0.5",
+      "resolved": "https://registry.npmjs.org/@types/dompurify/-/dompurify-3.0.5.tgz",
+      "integrity": "sha512-1Wg0g3BtQF7sSb27fJQAKck1HECM6zV1EB66j8JH9i3LCjYabJa0FSdiSgsD5K/RbrsR0SiraKacLB+T8ZVYAg==",
+      "license": "MIT",
+      "dependencies": {
+        "@types/trusted-types": "*"
+      }
+    },
     "node_modules/@types/estree": {
       "version": "1.0.8",
       "resolved": "https://registry.npmjs.org/@types/estree/-/estree-1.0.8.tgz",
@@ -2544,6 +2555,12 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@types/trusted-types": {
+      "version": "2.0.7",
+      "resolved": "https://registry.npmjs.org/@types/trusted-types/-/trusted-types-2.0.7.tgz",
+      "integrity": "sha512-ScaPdn1dQczgbl0QFTeTOmVHFULt394XJgOQNoyVhZ6r2vLnMLJfBPd53SB52T/3G36VI1/g2MZaX0cwDuXsfw==",
+      "license": "MIT"
+    },
     "node_modules/@types/unist": {
       "version": "3.0.3",
       "resolved": "https://registry.npmjs.org/@types/unist/-/unist-3.0.3.tgz",
@@ -3988,6 +4005,15 @@
         "csstype": "^3.0.2"
       }
     },
+    "node_modules/dompurify": {
+      "version": "3.4.10",
+      "resolved": "https://registry.npmjs.org/dompurify/-/dompurify-3.4.10.tgz",
+      "integrity": "sha512-0xzNv0e7oYC6yyuOGZIABPM4qtg3QxLFniDNPP4ZP90wR8Yq3zgwpRbrNiT4N3IKqDbbYFEJLV+JWEs19aZ//w==",
+      "license": "(MPL-2.0 OR Apache-2.0)",
+      "optionalDependencies": {
+        "@types/trusted-types": "^2.0.7"
+      }
+    },
     "node_modules/duck": {
       "version": "0.1.12",
       "resolved": "https://registry.npmjs.org/duck/-/duck-0.1.12.tgz",
diff --git a/frontend/package.json b/frontend/package.json
index b3be598e..d66587a1 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -12,8 +12,10 @@
   },
   "dependencies": {
     "@reduxjs/toolkit": "^2.11.2",
+    "@types/dompurify": "^3.0.5",
     "@xyflow/react": "^12.8.3",
     "antd": "^5.27.0",
+    "dompurify": "^3.4.10",
     "i18next": "^25.8.0",
     "jssha": "^3.3.1",
     "jszip": "^3.10.1",
diff --git a/frontend/src/components/file-preview/DocxPreview.tsx b/frontend/src/components/file-preview/DocxPreview.tsx
index 2249aac5..316d3345 100644
--- a/frontend/src/components/file-preview/DocxPreview.tsx
+++ b/frontend/src/components/file-preview/DocxPreview.tsx
@@ -1,4 +1,5 @@
 import React, { useEffect, useState } from 'react';
+import DOMPurify from 'dompurify';
 import mammoth from 'mammoth';
 
 export interface DocxPreviewProps {
@@ -28,7 +29,15 @@ export const DocxPreview: React.FC<DocxPreviewProps> = ({
 
         const arrayBuffer = await blob.arrayBuffer();
         const result = await mammoth.convertToHtml({ arrayBuffer });
-        setHtml(result.value);
+        // Sanitize HTML to prevent XSS from malicious DOCX files (FCE)
+        const sanitized = DOMPurify.sanitize(result.value, {
+          ALLOWED_TAGS: ['h1','h2','h3','h4','h5','h6','p','br','hr','ul','ol','li',
+            'table','thead','tbody','tr','th','td','strong','em','b','i','u','s',
+            'a','img','sup','sub','pre','code','blockquote','span','div'],
+          ALLOWED_ATTR: ['href','target','src','alt','width','height','colspan',
+            'rowspan','style','class','id','data-*'],
+        });
+        setHtml(sanitized);
       } catch (err) {
         setError('Failed to convert Word document');
       } finally {