diff --git a/src/hooks.server.ts b/src/hooks.server.ts
index 76a5bfe..4cd6e16 100644
--- a/src/hooks.server.ts
+++ b/src/hooks.server.ts
@@ -71,6 +71,8 @@ export const handle: Handle = async ({ event, resolve }) => {
 	response.headers.set('X-Frame-Options', 'DENY');
 	response.headers.set('X-Content-Type-Options', 'nosniff');
 	response.headers.set('Referrer-Policy', 'strict-origin-when-cross-origin');
+	response.headers.set('Strict-Transport-Security', 'max-age=31536000; includeSubDomains');
+	response.headers.set('Content-Security-Policy', "default-src 'self'; script-src 'self' 'unsafe-inline'; style-src 'self' 'unsafe-inline'; img-src 'self' data: blob:; font-src 'self'; connect-src 'self' ws: wss:; frame-ancestors 'none'");
 
 	logger.info({
 		method: event.request.method,
diff --git a/src/lib/server/ratelimit.ts b/src/lib/server/ratelimit.ts
index 8f95150..eb55031 100644
--- a/src/lib/server/ratelimit.ts
+++ b/src/lib/server/ratelimit.ts
@@ -42,6 +42,16 @@ export function registerLimiter(ip: string): RateLimitResult {
 	return rateLimit(ip, { window: 3_600_000, max: 5 });
 }
 
+/** Pre-configured: 5 password changes per 300s */
+export function passwordChangeLimiter(ip: string): RateLimitResult {
+	return rateLimit(ip, { window: 300_000, max: 5 });
+}
+
+/** Pre-configured: 20 file uploads per 60s */
+export function uploadLimiter(ip: string): RateLimitResult {
+	return rateLimit(ip, { window: 60_000, max: 20 });
+}
+
 // Periodic cleanup of stale entries every 60s
 setInterval(() => {
 	const now = Date.now();
diff --git a/src/routes/api/account/+server.ts b/src/routes/api/account/+server.ts
index e585929..cd29c54 100644
--- a/src/routes/api/account/+server.ts
+++ b/src/routes/api/account/+server.ts
@@ -3,6 +3,7 @@ import type { RequestHandler } from './$types.js';
 import { requireAuth } from '$lib/server/guards.js';
 import { hashPassword, verifyPassword } from '$lib/server/auth.js';
 import { withBypassRLS } from '$lib/server/rls.js';
+import { passwordChangeLimiter } from '$lib/server/ratelimit.js';
 import { z } from 'zod';
 
 const profileSchema = z.object({
@@ -16,13 +17,17 @@ const passwordSchema = z.object({
 });
 
 // Update profile
-export const PATCH: RequestHandler = async ({ request, locals }) => {
+export const PATCH: RequestHandler = async ({ request, locals, getClientAddress }) => {
 	requireAuth(locals.user);
 
 	const body = await request.json();
 
 	// Password change
 	if (body.currentPassword !== undefined) {
+		const limit = passwordChangeLimiter(getClientAddress());
+		if (!limit.ok) {
+			return json({ error: 'Too many attempts', retryAfter: limit.retryAfter }, { status: 429 });
+		}
 		const result = passwordSchema.safeParse(body);
 		if (!result.success) {
 			return json({ error: result.error.issues[0].message }, { status: 400 });
diff --git a/src/routes/api/account/avatar/+server.ts b/src/routes/api/account/avatar/+server.ts
index 5080958..8b0bfe1 100644
--- a/src/routes/api/account/avatar/+server.ts
+++ b/src/routes/api/account/avatar/+server.ts
@@ -2,14 +2,17 @@ import { json, error } from '@sveltejs/kit';
 import type { RequestHandler } from './$types.js';
 import { withBypassRLS } from '$lib/server/rls.js';
 import { requireAuth } from '$lib/server/guards.js';
+import { uploadLimiter } from '$lib/server/ratelimit.js';
 import { writeFile, mkdir, unlink } from 'fs/promises';
 import { join } from 'path';
 
 const MAX_SIZE = 2 * 1024 * 1024; // 2MB
 const UPLOAD_ROOT = '/app/uploads';
 
-export const POST: RequestHandler = async ({ request, locals }) => {
+export const POST: RequestHandler = async ({ request, locals, getClientAddress }) => {
 	requireAuth(locals.user);
+	const limit = uploadLimiter(getClientAddress());
+	if (!limit.ok) throw error(429, 'Too many uploads');
 
 	const formData = await request.formData();
 	const file = formData.get('avatar') as File | null;
diff --git a/src/routes/api/admin/branding/images/+server.ts b/src/routes/api/admin/branding/images/+server.ts
index ff444dd..95cf0a0 100644
--- a/src/routes/api/admin/branding/images/+server.ts
+++ b/src/routes/api/admin/branding/images/+server.ts
@@ -3,6 +3,7 @@ import type { RequestHandler } from './$types.js';
 import { withTenant } from '$lib/server/rls.js';
 import { requireTenantAdmin } from '$lib/server/guards.js';
 import { clearTenantCache } from '$lib/server/tenant.js';
+import { uploadLimiter } from '$lib/server/ratelimit.js';
 import { writeFile, mkdir, unlink } from 'fs/promises';
 import { join } from 'path';
 
@@ -19,10 +20,12 @@ const SLOT_TO_FIELD: Record<Slot, string> = {
 	'logo': 'logoUrl'
 };
 
-export const POST: RequestHandler = async ({ request, locals }) => {
+export const POST: RequestHandler = async ({ request, locals, getClientAddress }) => {
 	const tenant = locals.tenant;
 	if (!tenant) throw error(400, 'Unknown tenant');
 	requireTenantAdmin(locals.user);
+	const limit = uploadLimiter(getClientAddress());
+	if (!limit.ok) throw error(429, 'Too many uploads');
 
 	const formData = await request.formData();
 	const file = formData.get('file') as File | null;
diff --git a/src/routes/api/boards/[boardId]/columns/[columnId]/cards/[cardId]/attachments/+server.ts b/src/routes/api/boards/[boardId]/columns/[columnId]/cards/[cardId]/attachments/+server.ts
index a94a7c3..4256839 100644
--- a/src/routes/api/boards/[boardId]/columns/[columnId]/cards/[cardId]/attachments/+server.ts
+++ b/src/routes/api/boards/[boardId]/columns/[columnId]/cards/[cardId]/attachments/+server.ts
@@ -7,14 +7,25 @@ import { join } from 'path';
 import { randomUUID } from 'crypto';
 import { broadcast } from '$lib/server/realtime.js';
 import { logActivity } from '$lib/server/activity.js';
+import { uploadLimiter } from '$lib/server/ratelimit.js';
 
 const MAX_SIZE = 10 * 1024 * 1024; // 10MB
 const UPLOAD_ROOT = '/app/uploads';
+const ALLOWED_EXTENSIONS = new Set([
+	'.jpg', '.jpeg', '.png', '.gif', '.webp', '.svg',
+	'.pdf', '.doc', '.docx', '.xls', '.xlsx', '.ppt', '.pptx',
+	'.txt', '.csv', '.md', '.json', '.xml',
+	'.zip', '.gz', '.tar',
+	'.mp4', '.webm', '.mp3', '.wav'
+]);
 
-export const POST: RequestHandler = async ({ params, request, locals }) => {
+export const POST: RequestHandler = async ({ params, request, locals, getClientAddress }) => {
 	const tenant = locals.tenant;
 	if (!tenant) throw error(400, 'Unknown tenant');
 
+	const limit = uploadLimiter(getClientAddress());
+	if (!limit.ok) throw error(429, 'Too many uploads');
+
 	const formData = await request.formData();
 	const file = formData.get('file') as File | null;
 	if (!file) throw error(400, 'No file provided');
@@ -26,7 +37,8 @@ export const POST: RequestHandler = async ({ params, request, locals }) => {
 		const dir = join(UPLOAD_ROOT, tenant.id, params.cardId);
 		await mkdir(dir, { recursive: true });
 
-		const ext = file.name.includes('.') ? '.' + file.name.split('.').pop() : '';
+		const ext = file.name.includes('.') ? '.' + file.name.split('.').pop()!.toLowerCase() : '';
+		if (ext && !ALLOWED_EXTENSIONS.has(ext)) throw error(400, 'File type not allowed');
 		const storedName = randomUUID() + ext;
 		const filepath = join(dir, storedName);