diff --git a/lib/Controller/ApiController.php b/lib/Controller/ApiController.php
index 3ea7eb733..ae5a370bc 100644
--- a/lib/Controller/ApiController.php
+++ b/lib/Controller/ApiController.php
@@ -8,8 +8,8 @@
 
 namespace OCA\Photos\Controller;
 
+use JsonException;
 use OCA\Photos\AppInfo\Application;
-use OCA\Photos\Service\UserConfigService;
 use OCP\AppFramework\Controller;
 use OCP\AppFramework\Http;
 use OCP\AppFramework\Http\ContentSecurityPolicy;
@@ -50,14 +50,58 @@ public function setUserConfig(string $key, string $value): JSONResponse {
 			return new JSONResponse([], Http::STATUS_PRECONDITION_FAILED);
 		}
 
-		if (!in_array($key, array_keys(UserConfigService::DEFAULT_CONFIGS))) {
-			return new JSONResponse([], Http::STATUS_PRECONDITION_FAILED);
+		switch ($key) {
+			case 'croppedLayout':
+				if ($value !== 'true' && $value !== 'false') {
+					return new JSONResponse([], Http::STATUS_BAD_REQUEST);
+				}
+				break;
+			case 'photosLocation':
+				if (!$this->validatePath($value)) {
+					return new JSONResponse([], Http::STATUS_BAD_REQUEST);
+				}
+				break;
+			case 'photosSourceFolders':
+				try {
+					$paths = json_decode($value, true, 512, JSON_THROW_ON_ERROR);
+				} catch (JsonException) {
+					return new JSONResponse([], Http::STATUS_BAD_REQUEST);
+				}
+
+				if (!array_is_list($paths)) {
+					return new JSONResponse([], Http::STATUS_BAD_REQUEST);
+				}
+
+				foreach ($paths as $path) {
+					if (!$this->validatePath($path)) {
+						return new JSONResponse([], Http::STATUS_BAD_REQUEST);
+					}
+				}
+				break;
+			default:
+				return new JSONResponse([], Http::STATUS_BAD_REQUEST);
 		}
 
 		$this->config->setUserValue($user->getUid(), Application::APP_ID, $key, $value);
 		return new JSONResponse([], Http::STATUS_OK);
 	}
 
+	private function validatePath(mixed $path): bool {
+		if (!is_string($path)) {
+			return false;
+		}
+
+		if (!str_starts_with($path, '/')) {
+			return false;
+		}
+
+		if (str_contains($path, '..')) {
+			return false;
+		}
+
+		return true;
+	}
+
 	/**
 	 * @NoAdminRequired
 	 * @NoCSRFRequired
diff --git a/lib/Service/UserConfigService.php b/lib/Service/UserConfigService.php
index 80cd88d85..8257663bd 100644
--- a/lib/Service/UserConfigService.php
+++ b/lib/Service/UserConfigService.php
@@ -18,6 +18,7 @@ class UserConfigService {
 		'croppedLayout' => 'false',
 		'photosLocation' => '/Photos',
 		'photosSourceFolders' => '["/Photos"]',
+		/** If you add any new configs, make sure to validate the contents in {@see \OCA\Photos\Controller\ApiController::setUserConfig} */
 	];
 
 	private readonly IConfig $config;