From ef8fefa4eb1e190def91e4b14c4afa406b214359 Mon Sep 17 00:00:00 2001
From: Michel Weststrate <mweststrate@gmail.com>
Date: Wed, 20 Jan 2021 10:33:47 +0000
Subject: [PATCH] fix: Fixed security issue #738 when applying patches

Details: SNYK-JS-IMMER-1019369 / CVE-2020-28477
https://snyk.io/vuln/SNYK-JS-IMMER-1019369
---
 __tests__/patch.js     | 99 ++++++++++++++++++++++++++++++++++++++++++
 src/plugins/patches.ts | 13 +++++-
 src/utils/errors.ts    |  3 +-
 3 files changed, 113 insertions(+), 2 deletions(-)

diff --git a/__tests__/patch.js b/__tests__/patch.js
index 1d013b91..82d1ce3a 100644
--- a/__tests__/patch.js
+++ b/__tests__/patch.js
@@ -1147,3 +1147,102 @@ test("#676 patching Date objects", () => {
 	)
 	expect(rebuilt.date).toEqual(new Date("2020-11-10T08:08:08.003Z"))
 })
+
+test("do not allow __proto__ polution - 738", () => {
+	const obj = {}
+
+	// @ts-ignore
+	expect(obj.polluted).toBe(undefined)
+	expect(() => {
+		applyPatches({}, [
+			{op: "add", path: ["__proto__", "polluted"], value: "yes"}
+		])
+	}).toThrow(
+		"Patching reserved attributes like __proto__, prototype and constructor is not allowed"
+	)
+	// @ts-ignore
+	expect(obj.polluted).toBe(undefined)
+})
+
+test("do not allow __proto__ polution using arrays - 738", () => {
+	const obj = {}
+	const ar = []
+
+	// @ts-ignore
+	expect(obj.polluted).toBe(undefined)
+	// @ts-ignore
+	expect(ar.polluted).toBe(undefined)
+	expect(() => {
+		applyPatches(
+			[],
+			[{op: "add", path: ["__proto__", "polluted"], value: "yes"}]
+		)
+	}).toThrow(
+		"Patching reserved attributes like __proto__, prototype and constructor is not allowed"
+	)
+	// @ts-ignore
+	expect(obj.polluted).toBe(undefined)
+	// @ts-ignore
+	expect(ar.polluted).toBe(undefined)
+})
+
+test("do not allow prototype polution - 738", () => {
+	const obj = {}
+
+	// @ts-ignore
+	expect(obj.polluted).toBe(undefined)
+	expect(() => {
+		applyPatches(Object, [
+			{op: "add", path: ["prototype", "polluted"], value: "yes"}
+		])
+	}).toThrow(
+		"Patching reserved attributes like __proto__, prototype and constructor is not allowed"
+	)
+	// @ts-ignore
+	expect(obj.polluted).toBe(undefined)
+})
+
+test("do not allow constructor polution - 738", () => {
+	const obj = {}
+
+	// @ts-ignore
+	expect(obj.polluted).toBe(undefined)
+	const t = {}
+	applyPatches(t, [{op: "replace", path: ["constructor"], value: "yes"}])
+	expect(typeof t.constructor).toBe("function")
+	// @ts-ignore
+	expect(Object.polluted).toBe(undefined)
+})
+
+test("do not allow constructor.prototype polution - 738", () => {
+	const obj = {}
+
+	// @ts-ignore
+	expect(obj.polluted).toBe(undefined)
+	expect(() => {
+		applyPatches({}, [
+			{op: "add", path: ["constructor", "prototype", "polluted"], value: "yes"}
+		])
+	}).toThrow(
+		"Patching reserved attributes like __proto__, prototype and constructor is not allowed"
+	)
+	// @ts-ignore
+	expect(Object.polluted).toBe(undefined)
+})
+
+test("maps can store __proto__, prototype and constructor props", () => {
+	const obj = {}
+	const map = new Map()
+	map.set("__proto__", {})
+	map.set("constructor", {})
+	map.set("prototype", {})
+	const newMap = applyPatches(map, [
+		{op: "add", path: ["__proto__", "polluted"], value: "yes"},
+		{op: "add", path: ["constructor", "polluted"], value: "yes"},
+		{op: "add", path: ["prototype", "polluted"], value: "yes"}
+	])
+	expect(newMap.get("__proto__").polluted).toBe("yes")
+	expect(newMap.get("constructor").polluted).toBe("yes")
+	expect(newMap.get("prototype").polluted).toBe("yes")
+	expect(obj.polluted).toBe(undefined)
+})
diff --git a/src/plugins/patches.ts b/src/plugins/patches.ts
index 998627f2..1ad9a399 100644
--- a/src/plugins/patches.ts
+++ b/src/plugins/patches.ts
@@ -28,6 +28,8 @@ import {
 	isDraft,
 	isDraftable
 } from "../internal"
+import {applyPatches} from "../immer"
+import {ArchtypeObject} from "../types/types-internal"
 
 export function enablePatches() {
 	const REPLACE = "replace"
@@ -211,7 +213,16 @@ export function enablePatches() {
 
 			let base: any = draft
 			for (let i = 0; i < path.length - 1; i++) {
-				base = get(base, path[i])
+				const parentType = getArchtype(base)
+				const p = path[i]
+				// See #738, avoid prototype pollution
+				if (
+					(parentType === ArchtypeObject || parentType === ArchtypeArray) &&
+					(p === "__proto__" || p === "constructor")
+				)
+					die(24)
+				if (typeof base === "function" && p === "prototype") die(24)
+				base = get(base, p)
 				if (typeof base !== "object") die(15, path.join("/"))
 			}
 
diff --git a/src/utils/errors.ts b/src/utils/errors.ts
index b73e2aac..8cab0f9a 100644
--- a/src/utils/errors.ts
+++ b/src/utils/errors.ts
@@ -38,7 +38,8 @@ const errors = {
 	},
 	23(thing: string) {
 		return `'original' expects a draft, got: ${thing}`
-	}
+	},
+	24: "Patching reserved attributes like __proto__, prototype and constructor is not allowed"
 } as const
 
 export function die(error: keyof typeof errors, ...args: any[]): never {