diff --git a/src/constants/app.constants.ts b/src/constants/app.constants.ts
index 2cd48129..2e75f05e 100644
--- a/src/constants/app.constants.ts
+++ b/src/constants/app.constants.ts
@@ -42,3 +42,17 @@ export const STORAGE_KEYS = {
   PERF_TRENDS: 'teachlink:perf:trends',
   AUTH_TOKEN: 'token',
 };
+
+/**
+ * Domains permitted in sanitized HTML links and sanitizeUrl().
+ * Subdomains are automatically permitted (e.g. www.youtube.com matches youtube.com).
+ * Add entries here to extend the allowlist — one bare hostname per entry, no leading dot.
+ */
+export const ALLOWED_LINK_DOMAINS = [
+  'teachlink.com',
+  'youtube.com',
+  'youtube-nocookie.com',
+  'vimeo.com',
+  'github.com',
+  'loom.com',
+];
diff --git a/src/utils/__tests__/sanitize.test.ts b/src/utils/__tests__/sanitize.test.ts
new file mode 100644
index 00000000..7da4f99e
--- /dev/null
+++ b/src/utils/__tests__/sanitize.test.ts
@@ -0,0 +1,187 @@
+import { describe, it, expect } from 'vitest';
+import { sanitizeUrl, sanitizeHtml } from '../sanitize';
+
+// ---------------------------------------------------------------------------
+// sanitizeUrl – allowed domains
+// ---------------------------------------------------------------------------
+describe('sanitizeUrl – allowed domains', () => {
+  it('allows https on teachlink.com', () => {
+    expect(sanitizeUrl('https://teachlink.com/course/1')).toBe('https://teachlink.com/course/1');
+  });
+
+  it('allows subdomains of teachlink.com', () => {
+    expect(sanitizeUrl('https://app.teachlink.com/dashboard')).toBe('https://app.teachlink.com/dashboard');
+  });
+
+  it('allows http on teachlink.com', () => {
+    expect(sanitizeUrl('http://teachlink.com/')).toBe('http://teachlink.com/');
+  });
+
+  it('allows youtube.com', () => {
+    expect(sanitizeUrl('https://youtube.com/watch?v=dQw4w9WgXcQ')).not.toBeNull();
+  });
+
+  it('allows www.youtube.com (subdomain)', () => {
+    expect(sanitizeUrl('https://www.youtube.com/watch?v=abc')).not.toBeNull();
+  });
+
+  it('allows youtube-nocookie.com', () => {
+    expect(sanitizeUrl('https://www.youtube-nocookie.com/embed/abc')).not.toBeNull();
+  });
+
+  it('allows vimeo.com', () => {
+    expect(sanitizeUrl('https://vimeo.com/123456789')).not.toBeNull();
+  });
+
+  it('allows github.com', () => {
+    expect(sanitizeUrl('https://github.com/org/repo')).not.toBeNull();
+  });
+
+  it('allows URLs with query parameters and fragments', () => {
+    expect(sanitizeUrl('https://teachlink.com/search?q=test#results')).not.toBeNull();
+  });
+});
+
+// ---------------------------------------------------------------------------
+// sanitizeUrl – disallowed domains
+// ---------------------------------------------------------------------------
+describe('sanitizeUrl – disallowed domains', () => {
+  it('blocks arbitrary https destinations', () => {
+    expect(sanitizeUrl('https://evil.com/phishing')).toBeNull();
+  });
+
+  it('blocks domains that start with an allowed name but are not subdomains', () => {
+    expect(sanitizeUrl('https://teachlink.com.evil.com')).toBeNull();
+    expect(sanitizeUrl('https://noteachlink.com')).toBeNull();
+  });
+
+  it('blocks domains that end with an allowed name but have a different TLD', () => {
+    expect(sanitizeUrl('https://fakeyoutube.com')).toBeNull();
+  });
+
+  it('blocks URLs with ports on disallowed domains', () => {
+    expect(sanitizeUrl('https://evil.com:8080/attack')).toBeNull();
+  });
+});
+
+// ---------------------------------------------------------------------------
+// sanitizeUrl – protocol blocking
+// ---------------------------------------------------------------------------
+describe('sanitizeUrl – protocol blocking', () => {
+  it('blocks javascript: URIs', () => {
+    expect(sanitizeUrl('javascript:alert(1)')).toBeNull();
+  });
+
+  it('blocks data: URIs', () => {
+    expect(sanitizeUrl('data:text/html,<h1>XSS</h1>')).toBeNull();
+  });
+
+  it('blocks vbscript: URIs', () => {
+    expect(sanitizeUrl('vbscript:msgbox(1)')).toBeNull();
+  });
+
+  it('blocks ftp: URIs', () => {
+    expect(sanitizeUrl('ftp://teachlink.com/file')).toBeNull();
+  });
+});
+
+// ---------------------------------------------------------------------------
+// sanitizeUrl – edge cases
+// ---------------------------------------------------------------------------
+describe('sanitizeUrl – edge cases', () => {
+  it('returns null for empty string', () => {
+    expect(sanitizeUrl('')).toBeNull();
+  });
+
+  it('returns null for whitespace-only string', () => {
+    expect(sanitizeUrl('   ')).toBeNull();
+  });
+
+  it('returns null for relative URLs', () => {
+    expect(sanitizeUrl('/about')).toBeNull();
+  });
+
+  it('returns null for malformed URLs', () => {
+    expect(sanitizeUrl('not a url')).toBeNull();
+  });
+
+  it('trims surrounding whitespace before parsing', () => {
+    expect(sanitizeUrl('  https://teachlink.com/  ')).not.toBeNull();
+  });
+
+  it('returns null for URLs with authentication credentials on disallowed domains', () => {
+    expect(sanitizeUrl('https://user:pass@evil.com/')).toBeNull();
+  });
+
+  it('allows URLs with URL-encoded characters on allowed domains', () => {
+    expect(sanitizeUrl('https://teachlink.com/path%20with%20spaces')).not.toBeNull();
+  });
+});
+
+// ---------------------------------------------------------------------------
+// sanitizeHtml – DOMPurify hook enforces domain allowlist on hrefs
+// ---------------------------------------------------------------------------
+describe('sanitizeHtml – href domain enforcement', () => {
+  it('keeps href pointing to an allowed domain', () => {
+    const result = sanitizeHtml('<a href="https://teachlink.com/course">Course</a>');
+    expect(result).toContain('href="https://teachlink.com/course"');
+    expect(result).toContain('Course');
+  });
+
+  it('keeps href for youtube.com', () => {
+    const result = sanitizeHtml('<a href="https://www.youtube.com/watch?v=abc">Video</a>');
+    expect(result).toContain('href=');
+    expect(result).toContain('Video');
+  });
+
+  it('strips href pointing to a disallowed domain', () => {
+    const result = sanitizeHtml('<a href="https://evil.com/phishing">Click me</a>');
+    expect(result).not.toContain('href=');
+    expect(result).toContain('Click me');
+  });
+
+  it('strips href pointing to an arbitrary https destination', () => {
+    const result = sanitizeHtml('<a href="https://attacker.io/steal">Free gift</a>');
+    expect(result).not.toContain('href=');
+  });
+
+  it('strips javascript: hrefs (belt-and-suspenders with DOMPurify defaults)', () => {
+    const result = sanitizeHtml('<a href="javascript:alert(1)">XSS</a>');
+    expect(result).not.toContain('javascript:');
+  });
+
+  it('strips data: hrefs', () => {
+    const result = sanitizeHtml('<a href="data:text/html,<h1>x</h1>">data</a>');
+    expect(result).not.toContain('data:text');
+  });
+
+  it('allows relative hrefs (same-origin links)', () => {
+    const result = sanitizeHtml('<a href="/about">About</a>');
+    expect(result).toContain('href="/about"');
+  });
+
+  it('allows hash fragment hrefs', () => {
+    const result = sanitizeHtml('<a href="#section">Jump</a>');
+    expect(result).toContain('href="#section"');
+  });
+
+  it('preserves link text even when href is stripped', () => {
+    const result = sanitizeHtml('<a href="https://bad.example.com">Important text</a>');
+    expect(result).toContain('Important text');
+    expect(result).not.toContain('href=');
+  });
+
+  it('handles multiple links in one HTML string', () => {
+    const html =
+      '<a href="https://teachlink.com/">Good</a> <a href="https://evil.com/">Bad</a>';
+    const result = sanitizeHtml(html);
+    expect(result).toContain('href="https://teachlink.com/"');
+    expect(result).toContain('Good');
+    expect(result).toContain('Bad');
+    // The bad link should have its href removed
+    const badLinkMatch = result.match(/Bad/);
+    expect(badLinkMatch).not.toBeNull();
+    // Ensure evil.com doesn't appear anywhere
+    expect(result).not.toContain('evil.com');
+  });
+});
diff --git a/src/utils/sanitize.ts b/src/utils/sanitize.ts
index 175f2c73..d2c95da2 100644
--- a/src/utils/sanitize.ts
+++ b/src/utils/sanitize.ts
@@ -1,7 +1,35 @@
 import DOMPurify from 'dompurify';
+import { ALLOWED_LINK_DOMAINS } from '@/constants/app.constants';
 
 const SAFE_URL_SCHEMES = ['http:', 'https:'];
 
+/**
+ * Returns true when the hostname belongs to (or is a subdomain of) an allowlisted domain.
+ * e.g. "www.youtube.com" matches "youtube.com".
+ */
+const isAllowedDomain = (hostname: string): boolean =>
+  ALLOWED_LINK_DOMAINS.some((domain) => hostname === domain || hostname.endsWith(`.${domain}`));
+
+// Register the DOMPurify hook once at module load time.
+// It strips `href` attributes whose absolute URLs don't pass domain validation.
+// Relative URLs (e.g. "/about", "#section") are left untouched — they resolve to the same origin.
+let _hookRegistered = false;
+if (typeof window !== 'undefined' && !_hookRegistered) {
+  _hookRegistered = true;
+  DOMPurify.addHook('afterSanitizeAttributes', (node) => {
+    const href = node.getAttribute('href');
+    if (href === null) return;
+    try {
+      const parsed = new URL(href);
+      if (!SAFE_URL_SCHEMES.includes(parsed.protocol) || !isAllowedDomain(parsed.hostname)) {
+        node.removeAttribute('href');
+      }
+    } catch {
+      // new URL() throws for relative URLs — allow them (they stay on the same origin)
+    }
+  });
+}
+
 export const sanitizeHtml = (html: string): string => {
   if (typeof window === 'undefined') return html;
   return DOMPurify.sanitize(html, {
@@ -15,7 +43,9 @@ export const sanitizeUrl = (url: string): string | null => {
   if (!trimmed) return null;
   try {
     const parsed = new URL(trimmed);
-    return SAFE_URL_SCHEMES.includes(parsed.protocol) ? parsed.toString() : null;
+    if (!SAFE_URL_SCHEMES.includes(parsed.protocol)) return null;
+    if (!isAllowedDomain(parsed.hostname)) return null;
+    return parsed.toString();
   } catch {
     return null;
   }