From 55a408e810be9d3c384481666f64598568713db7 Mon Sep 17 00:00:00 2001
From: Timo Streule <48442147+tstreule@users.noreply.github.com>
Date: Fri, 15 May 2026 14:05:17 +0200
Subject: [PATCH] feat: allow img in HTML identity signatures

- Restricts src to https: URLs or base64-embedded raster data: URIs (png/jpeg/gif/webp).
- SVG is excluded for safety reasons.
- Images with a disallowed src are removed entirely so they don't render as broken-image icons.
---
 lib/__tests__/email-sanitization.test.ts | 73 +++++++++++++++++++++---
 lib/email-sanitization.ts                | 27 +++++++--
 2 files changed, 86 insertions(+), 14 deletions(-)

diff --git a/lib/__tests__/email-sanitization.test.ts b/lib/__tests__/email-sanitization.test.ts
index f36c5b50..1f9c2cb2 100644
--- a/lib/__tests__/email-sanitization.test.ts
+++ b/lib/__tests__/email-sanitization.test.ts
@@ -78,11 +78,67 @@ describe('email-sanitization', () => {
       expect(clean).toContain('John Doe');
     });
 
-    it('should remove images from signatures', () => {
-      const signature = '<p>John</p><img src="logo.png" alt="Logo">';
+    it('should allow img with https src', () => {
+      const signature = '<p>John</p><img src="https://cdn.example.com/logo.png" alt="Logo" width="120" height="40">';
       const clean = sanitizeSignatureHtml(signature);
+      expect(clean).toContain('<img');
+      expect(clean).toContain('src="https://cdn.example.com/logo.png"');
+      expect(clean).toContain('alt="Logo"');
+      expect(clean).toContain('width="120"');
+      expect(clean).toContain('height="40"');
+    });
+
+    it('should allow img with data:image/png;base64 src', () => {
+      const dataUri = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEX/AAAZ4gk3AAAAAXRSTlPM0jRW/QAAAAlwSFlzAAALEwAACxMBAJqcGAAAAA1JREFUCNdjYGBgAAAABAABc7Rs9wAAAABJRU5ErkJggg==';
+      const signature = `<img src="${dataUri}" alt="Logo">`;
+      const clean = sanitizeSignatureHtml(signature);
+      expect(clean).toContain('<img');
+      expect(clean).toContain('data:image/png;base64,');
+    });
+
+    it('should allow img with data:image/jpeg, gif, webp', () => {
+      const cases = ['data:image/jpeg;base64,AAA', 'data:image/jpg;base64,AAA', 'data:image/gif;base64,AAA', 'data:image/webp;base64,AAA'];
+      for (const src of cases) {
+        const clean = sanitizeSignatureHtml(`<img src="${src}" alt="x">`);
+        expect(clean).toContain('<img');
+        expect(clean).toContain(src);
+      }
+    });
+
+    it('should strip img with http: src (https only)', () => {
+      const signature = '<img src="http://insecure.example.com/logo.png" alt="Logo">';
+      const clean = sanitizeSignatureHtml(signature);
+      expect(clean).not.toContain('http://insecure.example.com');
       expect(clean).not.toContain('<img');
-      expect(clean).toContain('John');
+    });
+
+    it('should strip img with javascript: src', () => {
+      const signature = '<img src="javascript:alert(1)" alt="x">';
+      const clean = sanitizeSignatureHtml(signature);
+      expect(clean).not.toContain('javascript:');
+      expect(clean).not.toContain('<img');
+    });
+
+    it('should strip img with data:image/svg+xml src (SVG forbidden)', () => {
+      const signature = '<img src="data:image/svg+xml;base64,PHN2Zy8+" alt="x">';
+      const clean = sanitizeSignatureHtml(signature);
+      expect(clean).not.toContain('data:image/svg');
+      expect(clean).not.toContain('<img');
+    });
+
+    it('should strip img with non-image data: URI', () => {
+      const signature = '<img src="data:text/html;base64,PHA+aGk8L3A+" alt="x">';
+      const clean = sanitizeSignatureHtml(signature);
+      expect(clean).not.toContain('data:text/html');
+      expect(clean).not.toContain('<img');
+    });
+
+    it('should strip event handlers on img', () => {
+      const signature = '<img src="https://cdn.example.com/logo.png" alt="x" onerror="alert(1)" onload="alert(2)">';
+      const clean = sanitizeSignatureHtml(signature);
+      expect(clean).not.toContain('onerror');
+      expect(clean).not.toContain('onload');
+      expect(clean).toContain('https://cdn.example.com/logo.png');
     });
 
     it('should remove video and audio tags', () => {
@@ -113,16 +169,17 @@ describe('email-sanitization', () => {
     });
 
     it('should be stricter than email sanitization', () => {
-      const html = '<p>Text</p><img src="pic.jpg"><table><tr><td>Data</td></tr></table>';
+      const html = '<p>Text</p><table><tr><td>Data</td></tr></table><video src="v.mp4"></video>';
       const emailClean = sanitizeEmailHtml(html);
       const signatureClean = sanitizeSignatureHtml(html);
 
-      // Email allows img and table
-      expect(emailClean).toContain('<img');
+      // Email allows table
       expect(emailClean).toContain('<table>');
 
-      // Signature blocks img but may allow some tables (verify in implementation)
-      expect(signatureClean).not.toContain('<img');
+      // Signature blocks table and video
+      expect(signatureClean).not.toContain('<table');
+      expect(signatureClean).not.toContain('<video');
+      expect(signatureClean).toContain('Text');
     });
   });
 
diff --git a/lib/email-sanitization.ts b/lib/email-sanitization.ts
index 60c8076e..bee197f2 100644
--- a/lib/email-sanitization.ts
+++ b/lib/email-sanitization.ts
@@ -58,24 +58,39 @@ export function sanitizeEmailHtmlForIframe(html: string): string {
 
 /**
  * Sanitize HTML signature with stricter rules
- * Only allows basic formatting, no external resources
+ * Allows basic formatting plus <img> for company logos
  */
 export const SIGNATURE_SANITIZE_CONFIG = {
-  ALLOWED_TAGS: ['p', 'br', 'b', 'strong', 'i', 'em', 'u', 'a', 'span', 'div'],
-  ALLOWED_ATTR: ['href', 'style', 'class'],
+  ALLOWED_TAGS: ['p', 'br', 'b', 'strong', 'i', 'em', 'u', 'a', 'span', 'div', 'img'],
+  ALLOWED_ATTR: ['href', 'style', 'class', 'src', 'alt', 'width', 'height', 'title'],
   ALLOW_DATA_ATTR: false,
-  FORBID_TAGS: ['script', 'iframe', 'object', 'embed', 'img', 'video', 'audio'],
+  FORBID_TAGS: ['script', 'iframe', 'object', 'embed', 'video', 'audio'],
   FORBID_ATTR: ['onerror', 'onload', 'onclick', 'onmouseover'],
 };
 
 /**
- * Sanitize HTML signature for storage and display
+ * Sanitize HTML signature for storage and display.
+ * img src is restricted to https: or base64-embedded raster data: URIs
+ * (png/jpeg/gif/webp). SVG is excluded because DOMPurify cannot inspect
+ * bytes inside a data: URI. Images with a disallowed src are removed
+ * entirely so they don't render as broken-image icons.
  * @param html - User-provided HTML signature
  * @returns Sanitized signature (no scripts, no external resources)
  */
 export function sanitizeSignatureHtml(html: string): string {
   if (!html?.trim()) return '';
-  return DOMPurify.sanitize(html, SIGNATURE_SANITIZE_CONFIG);
+  DOMPurify.addHook('afterSanitizeAttributes', (node) => {
+    if (node.tagName !== 'IMG') return;
+    const src = node.getAttribute('src');
+    if (!src || !/^(?:https:\/\/|data:image\/(?:png|jpe?g|gif|webp);base64,)/i.test(src)) {
+      node.remove();
+    }
+  });
+  try {
+    return DOMPurify.sanitize(html, SIGNATURE_SANITIZE_CONFIG);
+  } finally {
+    DOMPurify.removeAllHooks();
+  }
 }
 
 /**