Shiro(CVE-2020-17523)权限绕过分析

一、前言

Apache Shiro是一个强大且易用的Java安全框架，执行身份验证、授权、密码和会话管理。使用Shiro的易于理解的API，您可以快速、轻松地获得任何应用程序，从最小的移动应用程序到最大的网络和企业应用程序。

当使用Spring配置Shiro的Filter时候，就有可能导致权限绕过的情况。

二、影响范围

Apache Shiro < 1.7.1

三、漏洞测试

本次实验通过SpringBoot搭建的环境，配置了Shiro的Filter路径，实验环境：https://github.com/jweny/shiro-cve-2020-17523

记住此处的authc对应的key是"/admin/*"

所以漏洞的poc就是：http://localhost:9090/admin/%20

四、漏洞分析

竟然是分析，我就从详细讲解下Shiro的Filter处理过程，先来看到刚才的Bean是通过ShiroFilterFactoryBean类来配置的Config属性，直接跟进去就能看到其中的getObject方法

getObject方法是实现了FactoryBean接口的方法

而这个instance变量是属于AbstractShiroFilter类

再来看看这个createInstance的方法

protected AbstractShiroFilter createInstance() throws Exception {

        log.debug("Creating Shiro Filter instance.");
        //获取shrio的安全管理容器
        SecurityManager securityManager = getSecurityManager();
        if (securityManager == null) {
            String msg = "SecurityManager property must be set.";
            throw new BeanInitializationException(msg);
        }

        if (!(securityManager instanceof WebSecurityManager)) {
            String msg = "The security manager does not implement the WebSecurityManager interface.";
            throw new BeanInitializationException(msg);
        }
        //获取过滤链管理器，就是shrio的全部过滤器，里面保存着路径和对应的过滤器或者过滤链
        FilterChainManager manager = createFilterChainManager();

        //Expose the constructed FilterChainManager by first wrapping it in a
        // FilterChainResolver implementation. The AbstractShiroFilter implementations
        // do not know about FilterChainManagers - only resolvers:
        //初始化Ant风格的url匹配器，传入上面的过滤链管理器
        PathMatchingFilterChainResolver chainResolver = new PathMatchingFilterChainResolver();
        chainResolver.setFilterChainManager(manager);

        //Now create a concrete ShiroFilter instance and apply the acquired SecurityManager and built
        //FilterChainResolver.  It doesn't matter that the instance is an anonymous inner class
        //here - we're just using it because it is a concrete AbstractShiroFilter instance that accepts
        //injection of the SecurityManager and FilterChainResolver:
        //初始化门户过滤器，所有请求都应该经过这个过滤器
        return new SpringShiroFilter((WebSecurityManager) securityManager, chainResolver);
    }