diff --git a/packages/app/src/TransformRequest/MultipartFormDataTransform.ts b/packages/app/src/TransformRequest/MultipartFormDataTransform.ts
index 6e68587e..2267590b 100644
--- a/packages/app/src/TransformRequest/MultipartFormDataTransform.ts
+++ b/packages/app/src/TransformRequest/MultipartFormDataTransform.ts
@@ -17,10 +17,9 @@ export const MultipartFormDataTransform = async <T = unknown>(request: IRequest)
 
     const rs = await request.createReadableStream();
     const defer = new Defer<void>();
-    const result: Record<string, any> = {};
     const pending: Defer<void>[] = [];
 
-    const {parseFieldName, inject} = QueryString;
+    const qs = new QueryString();
 
     bb
         .on("file", (name, file, info) => {
@@ -37,7 +36,7 @@ export const MultipartFormDataTransform = async <T = unknown>(request: IRequest)
                 tmpname,
             };
 
-            inject(parseFieldName(name), value, result);
+            qs.push(name, value);
 
             const def = new Defer<void>();
             pending.push(def);
@@ -48,7 +47,7 @@ export const MultipartFormDataTransform = async <T = unknown>(request: IRequest)
         })
         .on("field", (name, value) => {
             try {
-                inject(parseFieldName(name), JSON.parse(value), result);
+                qs.push(name, JSON.parse(value));
             } catch {
                 // skip
             }
@@ -60,5 +59,5 @@ export const MultipartFormDataTransform = async <T = unknown>(request: IRequest)
     await defer;
     await Promise.all(pending);
 
-    return result as any;
+    return qs.toObject();
 };
diff --git a/packages/util/src/qs.ts b/packages/util/src/qs.ts
index 12420f6b..14715bd2 100644
--- a/packages/util/src/qs.ts
+++ b/packages/util/src/qs.ts
@@ -1,15 +1,34 @@
+import {Rec} from "@bunt/type";
+
 const isNumeric = (key: string): boolean => !isNaN(+key);
 
 export class QueryString {
-    public static parseFieldName = (name: string): string[] => {
+    readonly #value: Rec;
+
+    constructor(entries: [field: string, value: unknown][] = []) {
+        this.#value = Object.create(null);
+        for (const [field, value] of entries) {
+            this.push(field, value);
+        }
+    }
+
+    public parseField(name: string): string[] {
         const base = name.replace(/\[.+/, "");
 
         return [base, ...[...name.matchAll(/\[([^\]]*)\]/ig)].map(([, key]) => key)];
-    };
+    }
+
+    public push(name: string, value: unknown): Rec {
+        return this.#inject(this.parseField(name), value, this.#value);
+    }
+
+    public toObject(): Rec {
+        return this.#value;
+    }
 
-    public static inject = ([key, ...paths]: string[], value: unknown, fields: any = {}): any => {
+    #inject = ([key, ...paths]: string[], value: unknown, fields: Rec = Object.create(null)): Rec => {
         if (paths.length > 0) {
-            fields[key] = this.inject(paths, value, fields[key]);
+            fields[key] = this.#inject(paths, value, fields[key]);
         } else {
             fields[key] = value;
         }
diff --git a/packages/util/test/src/qs/QueryStirng.test.ts b/packages/util/test/src/qs/QueryStirng.test.ts
index 7e35f7e4..4fc660a9 100644
--- a/packages/util/test/src/qs/QueryStirng.test.ts
+++ b/packages/util/test/src/qs/QueryStirng.test.ts
@@ -1,34 +1,45 @@
 import {QueryString} from "../../../src";
 
 describe("QueryString", () => {
+    test("Prevent pollution", () => {
+        const injectTest = {};
+        const injectKey = "__proto__[polluted]";
+
+        const qs = new QueryString();
+        qs.push(injectKey, true);
+
+        expect(Reflect.has(Reflect.get(injectTest, "__proto__"), "polluted")).toBeFalsy();
+    });
+
     test("Base", () => {
+        const qs = new QueryString();
         const field = "foo[bar][baz][0]";
-        const parsed = QueryString.parseFieldName(field);
+        const parsed = qs.parseField(field);
 
         expect(parsed)
             .toEqual(["foo", "bar", "baz", "0"]);
 
-        expect(QueryString.inject(parsed, 1))
+        expect(qs.push(field, 1))
             .toEqual({foo: {bar: {baz: [1]}}});
     });
 
     test("Array", () => {
+        const qs = new QueryString();
         const map: [string, any][] = [
             ["foo[0]", 1],
             ["foo[1]", 2],
             ["foo[2]", 3],
         ];
 
-        const result = {};
         for (const [field, value] of map) {
-            const paths = QueryString.parseFieldName(field);
-            QueryString.inject(paths, value, result);
+            qs.push(field, value);
         }
 
-        expect(result).toEqual({foo: [1, 2, 3]});
+        expect(qs.toObject()).toEqual({foo: [1, 2, 3]});
     });
 
     test("Nested array", () => {
+        const qs = new QueryString();
         const map: [string, any][] = [
             ["foo[0][a]", 1],
             ["foo[0][b]", 2],
@@ -36,13 +47,11 @@ describe("QueryString", () => {
             ["foo[1][d]", 4],
         ];
 
-        const result = {};
         for (const [field, value] of map) {
-            const paths = QueryString.parseFieldName(field);
-            QueryString.inject(paths, value, result);
+            qs.push(field, value);
         }
 
-        expect(result).toEqual({foo: [{a: 1, b: 2}, {c: 3, d: 4}]});
+        expect(qs.toObject()).toEqual({foo: [{a: 1, b: 2}, {c: 3, d: 4}]});
     });
 
     test.each([
@@ -50,8 +59,8 @@ describe("QueryString", () => {
         ["foo[bar]", 1, {foo: {bar: 1}}],
         ["foo[bar][0]", 1, {foo: {bar: [1]}}],
         ["foo[0][bar]", 1, {foo: [{bar: 1}]}],
-    ])("Variants", (field, value, res) => (
-        expect(QueryString.inject(QueryString.parseFieldName(field), value))
-            .toEqual(res)
-    ));
+    ])("Variants", (field, value, res) => {
+        const qs = new QueryString([[field, value]]);
+        expect(qs.toObject()).toEqual(res);
+    });
 });