diff --git a/client/src/components/modal/brief-info.tsx b/client/src/components/modal/brief-info.tsx
index 78c394d..718a2cd 100644
--- a/client/src/components/modal/brief-info.tsx
+++ b/client/src/components/modal/brief-info.tsx
@@ -26,6 +26,11 @@ const BriefInfo: React.FC<RegisterDataProps> = ({ registerData, setRegisterData
 
     const handleInputChange = useCallback((e: React.ChangeEvent<HTMLInputElement>) => {
         const { name, value } = e.target;
+        const specialCharRegex = /[!@#$%^&*()_+\-=\[\]{};':"\\|,.<>\/?]/;
+        if (specialCharRegex.test(value)) {
+            return toast.warning('Special characters not allowed.');
+        }
+
         setRegisterData(prevState => ({
             ...prevState,
             [name]: value
diff --git a/server/routes/auth.js b/server/routes/auth.js
index 9852693..fba5701 100644
--- a/server/routes/auth.js
+++ b/server/routes/auth.js
@@ -9,9 +9,9 @@ module.exports = async function (fastify, opts) {
                 email: { type: 'string', format: 'email', minLength: 1 },
                 password: { type: 'string', minLength: 6 },
                 avatar: { type: 'string', nullable: true },
-                username: { type: 'string', minLength: 1 },
-                first_name: { type: 'string', minLength: 1 },
-                last_name: { type: 'string', minLength: 1 }
+                username: { type: 'string', minLength: 1, pattern: '^[a-zA-Z0-9]+$' },
+                first_name: { type: 'string', minLength: 1, pattern: '^[a-zA-Z0-9]+$' },
+                last_name: { type: 'string', minLength: 1, pattern: '^[a-zA-Z0-9]+$' }
             },
             required: ['email', 'password', 'username', 'first_name', 'last_name']
         }