Java字符串如何变为不可变增加安全性？ [英] How does Java string being immutable increase security?

问题描述

我是Java新手，在学习时，我发现 String 是不可变的。当我阅读其背后的原因时，出现了一些原因，例如性能提升，因为它的值无法修改，并且可以由多个线程共享。这些原因我明白了。

但我不知道它与安全性有什么关系。 String 如何在Java安全性中成为不可变的帮助？

I am new to Java and when learning, I came across the fact that a String is immutable. When I was reading the reason behind it, a few reasons came up, for example performance increasements, since its value cannot be modified, and it can be shared by multiple threads. These reasons I do understand.
But I don't get how it is related to security. How does a String being immutable help in Java security?

请帮助我理解。在此先感谢。

Please help me in understanding. Thanks in advance.

推荐答案

编写类库的一种常见做法是存储传递到API中的参数，例如，构造函数，像这样：

A very common practice in writing class libraries is storing the parameters passed into your API, say, in a constructor, like this:

public class MyApi {
    final String myUrl;
    public MyApi(String urlString) {
        // Verify that urlString points to an approved server
        if (!checkApprovedUrl(urlString)) throw new IllegalArgumentException();
        myUrl = urlString;
    }
}

是字符串 mutable，这会导致一个微妙的漏洞：攻击者会传递一个好的URL，等待几微秒，然后将URL设置为指向攻击站点。

Were String mutable, this would lead to a subtle exploit: an attacker would pass a good URL, wait for a few microseconds, and then set the URL to point to an attack site.

由于存储而不进行复制是一种相当普遍的做法，并且由于字符串是最常用的数据类型之一，因此保留字符串可变性会打开许多​​尚未编写但仍然存在严重安全问题的API。使字符串不可变会关闭所有API的特定安全漏洞，包括尚未编写的API。

Since storing without copying is a reasonably common practice, and because strings are among the most commonly used data types, leaving strings mutable would open up many APIs that are not written yet open to a serious security problem. Making strings immutable closes this particular security hole for all APIs, including the ones that are not written yet.

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