diff --git a/src/auth.ts b/src/auth.ts
index 411ece9..19b0e61 100644
--- a/src/auth.ts
+++ b/src/auth.ts
@@ -125,7 +125,7 @@ const authConfig: SvelteKitAuthConfig = {
 		}
 	},
 	secret: env.AUTH_SECRET,
-	trustHost: true
+	trustHost: env.AUTH_TRUST_HOST === 'true'
 };
 
 export const { handle, signIn, signOut } = SvelteKitAuth(authConfig);
diff --git a/src/lib/server/validation.ts b/src/lib/server/validation.ts
new file mode 100644
index 0000000..18335af
--- /dev/null
+++ b/src/lib/server/validation.ts
@@ -0,0 +1,86 @@
+export function sanitizeString(input: string | null | undefined, maxLength: number = 1000): string | null {
+	if (input === null || input === undefined) {
+		return null;
+	}
+	const trimmed = input.trim();
+	if (trimmed.length > maxLength) {
+		throw new Error(`Input exceeds maximum length of ${maxLength}`);
+	}
+	return trimmed;
+}
+
+export function sanitizeUrl(url: string | null | undefined): string | null {
+	if (!url) {
+		return null;
+	}
+	return url.trim();
+}
+
+export function sanitizeText(input: string | null | undefined, maxLength: number = 10000): string | null {
+	if (input === null || input === undefined) {
+		return null;
+	}
+	const trimmed = input.trim();
+	if (trimmed.length > maxLength) {
+		throw new Error(`Text exceeds maximum length of ${maxLength}`);
+	}
+	return trimmed;
+}
+
+export function sanitizePrice(price: string | null | undefined): number | null {
+	if (!price) {
+		return null;
+	}
+	const parsed = parseFloat(price.trim());
+	if (isNaN(parsed)) {
+		throw new Error('Invalid price format');
+	}
+	if (parsed < 0) {
+		throw new Error('Price cannot be negative');
+	}
+	return parsed;
+}
+
+export function sanitizeColor(color: string | null | undefined): string | null {
+	if (!color) {
+		return null;
+	}
+	return color.trim();
+}
+
+export function sanitizeCurrency(currency: string | null | undefined): string {
+	if (!currency) {
+		return 'DKK';
+	}
+	return currency.trim().toUpperCase();
+}
+
+export function sanitizeUsername(username: string): string {
+	const trimmed = username.trim().toLowerCase();
+	if (trimmed.length < 3 || trimmed.length > 50) {
+		throw new Error('Username must be between 3 and 50 characters');
+	}
+	return trimmed;
+}
+
+export function sanitizeId(id: string | null | undefined): string {
+	if (!id) {
+		throw new Error('ID is required');
+	}
+	const trimmed = id.trim();
+	if (trimmed.length === 0 || trimmed.length > 100) {
+		throw new Error('Invalid ID');
+	}
+	return trimmed;
+}
+
+export function sanitizeToken(token: string | null | undefined): string {
+	if (!token) {
+		throw new Error('Token is required');
+	}
+	const trimmed = token.trim();
+	if (trimmed.length === 0 || trimmed.length > 100) {
+		throw new Error('Invalid token');
+	}
+	return trimmed;
+}
\ No newline at end of file
diff --git a/src/routes/api/image-proxy/+server.ts b/src/routes/api/image-proxy/+server.ts
index 6ce75f3..f15e262 100644
--- a/src/routes/api/image-proxy/+server.ts
+++ b/src/routes/api/image-proxy/+server.ts
@@ -1,5 +1,21 @@
 import type { RequestHandler } from './$types';
 
+function isValidImageUrl(url: string): boolean {
+	try {
+		const parsedUrl = new URL(url);
+		if (!['http:', 'https:'].includes(parsedUrl.protocol)) {
+			return false;
+		}
+		const hostname = parsedUrl.hostname.toLowerCase();
+		if (hostname === 'localhost' || hostname === '127.0.0.1' || hostname === '::1') {
+			return false;
+		}
+		return true;
+	} catch {
+		return false;
+	}
+}
+
 export const GET: RequestHandler = async ({ url }) => {
 	const imageUrl = url.searchParams.get('url');
 
@@ -7,6 +23,10 @@ export const GET: RequestHandler = async ({ url }) => {
 		return new Response('Image URL is required', { status: 400 });
 	}
 
+	if (!isValidImageUrl(imageUrl)) {
+		return new Response('Invalid image URL', { status: 400 });
+	}
+
 	try {
 		// Fetch the image with proper headers to avoid blocking
 		const response = await fetch(imageUrl, {
diff --git a/src/routes/api/scrape-images/+server.ts b/src/routes/api/scrape-images/+server.ts
index a1400d3..a4515dd 100644
--- a/src/routes/api/scrape-images/+server.ts
+++ b/src/routes/api/scrape-images/+server.ts
@@ -1,6 +1,22 @@
 import { json } from '@sveltejs/kit';
 import type { RequestHandler } from './$types';
 
+function isValidUrl(urlString: string): boolean {
+	try {
+		const url = new URL(urlString);
+		if (!['http:', 'https:'].includes(url.protocol)) {
+			return false;
+		}
+		const hostname = url.hostname.toLowerCase();
+		if (hostname === 'localhost' || hostname === '127.0.0.1' || hostname === '::1') {
+			return false;
+		}
+		return true;
+	} catch {
+		return false;
+	}
+}
+
 export const POST: RequestHandler = async ({ request }) => {
 	const { url } = await request.json();
 
@@ -8,6 +24,10 @@ export const POST: RequestHandler = async ({ request }) => {
 		return json({ error: 'URL is required' }, { status: 400 });
 	}
 
+	if (!isValidUrl(url)) {
+		return json({ error: 'Invalid URL' }, { status: 400 });
+	}
+
 	try {
 		const response = await fetch(url, {
 			headers: {
diff --git a/src/routes/api/wishlists/+server.ts b/src/routes/api/wishlists/+server.ts
index e43bd16..c70e3a4 100644
--- a/src/routes/api/wishlists/+server.ts
+++ b/src/routes/api/wishlists/+server.ts
@@ -3,11 +3,24 @@ import type { RequestHandler } from './$types';
 import { db } from '$lib/server/db';
 import { wishlists } from '$lib/server/schema';
 import { createId } from '@paralleldrive/cuid2';
+import { sanitizeString, sanitizeColor } from '$lib/server/validation';
 
 export const POST: RequestHandler = async ({ request, locals }) => {
-	const { title, description, color } = await request.json();
+	const body = await request.json();
 
-	if (!title?.trim()) {
+	let title: string | null;
+	let description: string | null;
+	let color: string | null;
+
+	try {
+		title = sanitizeString(body.title, 200);
+		description = sanitizeString(body.description, 2000);
+		color = sanitizeColor(body.color);
+	} catch (error) {
+		return json({ error: 'Invalid input' }, { status: 400 });
+	}
+
+	if (!title) {
 		return json({ error: 'Title is required' }, { status: 400 });
 	}
 
@@ -20,9 +33,9 @@ export const POST: RequestHandler = async ({ request, locals }) => {
 	const [wishlist] = await db
 		.insert(wishlists)
 		.values({
-			title: title.trim(),
-			description: description?.trim() || null,
-			color: color?.trim() || null,
+			title,
+			description,
+			color,
 			ownerToken,
 			publicToken,
 			userId
diff --git a/src/routes/signup/+page.server.ts b/src/routes/signup/+page.server.ts
index 017eb8b..0533980 100644
--- a/src/routes/signup/+page.server.ts
+++ b/src/routes/signup/+page.server.ts
@@ -5,6 +5,7 @@ import { users } from '$lib/server/schema';
 import { eq } from 'drizzle-orm';
 import bcrypt from 'bcrypt';
 import { env } from '$env/dynamic/private';
+import { sanitizeString, sanitizeUsername } from '$lib/server/validation';
 
 export const load: PageServerLoad = async () => {
 	// Determine which OAuth providers are available
@@ -31,12 +32,18 @@ export const actions: Actions = {
 		const password = formData.get('password') as string;
 		const confirmPassword = formData.get('confirmPassword') as string;
 
-		if (!name?.trim()) {
-			return fail(400, { error: 'Name is required', name, username });
+		let sanitizedUsername: string;
+		let sanitizedName: string | null;
+
+		try {
+			sanitizedName = sanitizeString(name, 100);
+			sanitizedUsername = sanitizeUsername(username);
+		} catch (error) {
+			return fail(400, { error: 'Invalid input', name, username });
 		}
 
-		if (!username?.trim()) {
-			return fail(400, { error: 'Username is required', name, username });
+		if (!sanitizedName) {
+			return fail(400, { error: 'Name is required', name, username });
 		}
 
 		if (!password || password.length < 8) {
@@ -48,7 +55,7 @@ export const actions: Actions = {
 		}
 
 		const existingUser = await db.query.users.findFirst({
-			where: eq(users.username, username.trim().toLowerCase())
+			where: eq(users.username, sanitizedUsername)
 		});
 
 		if (existingUser) {
@@ -58,8 +65,8 @@ export const actions: Actions = {
 		const hashedPassword = await bcrypt.hash(password, 10);
 
 		await db.insert(users).values({
-			name: name.trim(),
-			username: username.trim().toLowerCase(),
+			name: sanitizedName,
+			username: sanitizedUsername,
 			password: hashedPassword
 		});
 
diff --git a/src/routes/wishlist/[token]/+page.server.ts b/src/routes/wishlist/[token]/+page.server.ts
index 0c77ca2..b179547 100644
--- a/src/routes/wishlist/[token]/+page.server.ts
+++ b/src/routes/wishlist/[token]/+page.server.ts
@@ -34,7 +34,7 @@ export const load: PageServerLoad = async ({ params, locals }) => {
 			)
 		});
 		isSaved = !!saved;
-		isClaimed = !!saved?.ownerToken; // User has claimed if ownerToken exists in savedWishlists
+		isClaimed = !!saved?.ownerToken;
 		savedWishlistId = saved?.id || null;
 	}