diff --git a/packages/core/src/routes/public-forms.test.ts b/packages/core/src/routes/public-forms.test.ts
new file mode 100644
index 000000000..a1e9587db
--- /dev/null
+++ b/packages/core/src/routes/public-forms.test.ts
@@ -0,0 +1,220 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest'
+import { Hono } from 'hono'
+
+// Track what gets stored
+let capturedSubmissionData: string | null = null
+
+// Mock TurnstileService — disabled by default so submissions go through
+vi.mock('../plugins/core-plugins/turnstile-plugin/services/turnstile', () => ({
+  TurnstileService: class MockTurnstileService {
+    getSettings = vi.fn().mockResolvedValue(null)
+    isEnabled = vi.fn().mockResolvedValue(false)
+    verifyToken = vi.fn().mockResolvedValue({ success: true })
+  }
+}))
+
+import { publicFormsRoutes } from './public-forms'
+
+function createMockDb(formExists = true) {
+  return {
+    prepare: vi.fn().mockImplementation((sql: string) => {
+      // Form lookup
+      if (sql.includes('FROM forms WHERE')) {
+        return {
+          bind: vi.fn().mockReturnThis(),
+          first: vi.fn().mockResolvedValue(
+            formExists
+              ? {
+                  id: 'form-1',
+                  name: 'test_form',
+                  display_name: 'Test Form',
+                  is_active: 1,
+                  turnstile_enabled: 0,
+                  turnstile_settings: null
+                }
+              : null
+          ),
+          all: vi.fn().mockResolvedValue({ results: [] }),
+          run: vi.fn().mockResolvedValue({ success: true })
+        }
+      }
+      // INSERT into form_submissions — capture the data
+      if (sql.includes('INSERT INTO form_submissions')) {
+        return {
+          bind: vi.fn().mockImplementation((...args: any[]) => {
+            // submission_data is the 3rd bound param (index 2)
+            capturedSubmissionData = args[2]
+            return {
+              run: vi.fn().mockResolvedValue({ success: true }),
+              first: vi.fn().mockResolvedValue(null),
+              all: vi.fn().mockResolvedValue({ results: [] })
+            }
+          }),
+          run: vi.fn().mockResolvedValue({ success: true }),
+          first: vi.fn().mockResolvedValue(null),
+          all: vi.fn().mockResolvedValue({ results: [] })
+        }
+      }
+      // UPDATE forms (submission count)
+      if (sql.includes('UPDATE forms')) {
+        return {
+          bind: vi.fn().mockReturnThis(),
+          run: vi.fn().mockResolvedValue({ success: true }),
+          first: vi.fn().mockResolvedValue(null),
+          all: vi.fn().mockResolvedValue({ results: [] })
+        }
+      }
+      // Default
+      return {
+        bind: vi.fn().mockReturnThis(),
+        first: vi.fn().mockResolvedValue(null),
+        all: vi.fn().mockResolvedValue({ results: [] }),
+        run: vi.fn().mockResolvedValue({ success: true })
+      }
+    })
+  }
+}
+
+function createTestApp(db: any) {
+  const app = new Hono()
+
+  app.use('/api/forms/*', async (c, next) => {
+    c.env = { DB: db } as any
+    await next()
+  })
+
+  app.route('/api/forms', publicFormsRoutes)
+  return app
+}
+
+describe('POST /api/forms/:identifier/submit — XSS sanitization', () => {
+  beforeEach(() => {
+    vi.clearAllMocks()
+    capturedSubmissionData = null
+  })
+
+  it('should HTML-encode script tags in string fields', async () => {
+    const db = createMockDb()
+    const app = createTestApp(db)
+
+    const res = await app.request('/api/forms/form-1/submit', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({
+        data: {
+          name: 'John',
+          comment: '<script>alert("xss")</script>'
+        }
+      })
+    })
+
+    const json = await res.json() as any
+    expect(res.status).toBe(200)
+    expect(json.success).toBe(true)
+
+    // Verify stored data has encoded HTML
+    const stored = JSON.parse(capturedSubmissionData!)
+    expect(stored.name).toBe('John')
+    expect(stored.comment).toBe('&lt;script&gt;alert(&quot;xss&quot;)&lt;/script&gt;')
+  })
+
+  it('should sanitize nested objects recursively', async () => {
+    const db = createMockDb()
+    const app = createTestApp(db)
+
+    const res = await app.request('/api/forms/form-1/submit', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({
+        data: {
+          user: {
+            name: '<img src=x onerror=alert(1)>',
+            address: {
+              street: '123 Main St',
+              city: '<b>Baltimore</b>'
+            }
+          }
+        }
+      })
+    })
+
+    expect(res.status).toBe(200)
+    const stored = JSON.parse(capturedSubmissionData!)
+    expect(stored.user.name).toBe('&lt;img src=x onerror=alert(1)&gt;')
+    expect(stored.user.address.street).toBe('123 Main St')
+    expect(stored.user.address.city).toBe('&lt;b&gt;Baltimore&lt;/b&gt;')
+  })
+
+  it('should sanitize arrays of strings', async () => {
+    const db = createMockDb()
+    const app = createTestApp(db)
+
+    const res = await app.request('/api/forms/form-1/submit', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({
+        data: {
+          tags: ['safe', '<script>bad</script>', 'also safe']
+        }
+      })
+    })
+
+    expect(res.status).toBe(200)
+    const stored = JSON.parse(capturedSubmissionData!)
+    expect(stored.tags).toEqual([
+      'safe',
+      '&lt;script&gt;bad&lt;/script&gt;',
+      'also safe'
+    ])
+  })
+
+  it('should pass through numbers, booleans, and null unchanged', async () => {
+    const db = createMockDb()
+    const app = createTestApp(db)
+
+    const res = await app.request('/api/forms/form-1/submit', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({
+        data: {
+          age: 25,
+          active: true,
+          optional: null,
+          name: 'Test'
+        }
+      })
+    })
+
+    expect(res.status).toBe(200)
+    const stored = JSON.parse(capturedSubmissionData!)
+    expect(stored.age).toBe(25)
+    expect(stored.active).toBe(true)
+    expect(stored.optional).toBeNull()
+    expect(stored.name).toBe('Test')
+  })
+
+  it('should handle event handler injection attempts', async () => {
+    const db = createMockDb()
+    const app = createTestApp(db)
+
+    const res = await app.request('/api/forms/form-1/submit', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({
+        data: {
+          field1: '" onmouseover="alert(1)',
+          field2: "' onclick='alert(1)'",
+          field3: '<img src=x onerror=alert(1)>'
+        }
+      })
+    })
+
+    expect(res.status).toBe(200)
+    const stored = JSON.parse(capturedSubmissionData!)
+    // All angle brackets and quotes should be encoded
+    expect(stored.field1).not.toContain('"')
+    expect(stored.field2).not.toContain("'")
+    expect(stored.field3).not.toContain('<')
+    expect(stored.field3).not.toContain('>')
+  })
+})
diff --git a/packages/core/src/routes/public-forms.ts b/packages/core/src/routes/public-forms.ts
index a525ce883..229889c0d 100644
--- a/packages/core/src/routes/public-forms.ts
+++ b/packages/core/src/routes/public-forms.ts
@@ -1,5 +1,28 @@
 import { Hono } from 'hono'
 import { TurnstileService } from '../plugins/core-plugins/turnstile-plugin/services/turnstile'
+import { sanitizeInput } from '../utils/sanitize'
+
+/**
+ * Recursively sanitize all string values in arbitrary JSON data.
+ * HTML-encodes entities (e.g., < becomes &lt;) to prevent stored XSS
+ * when form submission data is rendered in admin templates.
+ */
+function sanitizeDeep(value: unknown): unknown {
+  if (typeof value === 'string') {
+    return sanitizeInput(value)
+  }
+  if (Array.isArray(value)) {
+    return value.map(sanitizeDeep)
+  }
+  if (value !== null && typeof value === 'object') {
+    const result: Record<string, unknown> = {}
+    for (const [k, v] of Object.entries(value)) {
+      result[k] = sanitizeDeep(v)
+    }
+    return result
+  }
+  return value // numbers, booleans, null pass through
+}
 
 type Bindings = {
   DB: D1Database
@@ -538,6 +561,10 @@ publicFormsRoutes.post('/:identifier/submit', async (c) => {
       }
     }
 
+    // Sanitize all string values in submission data to prevent stored XSS.
+    // HTML-encodes entities (e.g., < becomes &lt;) before storage.
+    const sanitizedData = sanitizeDeep(body.data) as Record<string, unknown>
+
     // Create submission
     const submissionId = crypto.randomUUID()
     const now = Date.now()
@@ -550,7 +577,7 @@ publicFormsRoutes.post('/:identifier/submit', async (c) => {
     `).bind(
       submissionId,
       form.id,
-      JSON.stringify(body.data),
+      JSON.stringify(sanitizedData),
       null, // user_id (for authenticated users)
       c.req.header('cf-connecting-ip') || null,
       c.req.header('user-agent') || null,