Springboot devtools <=2.6.4 rce

Devtools is a hot deployment tool of spring boot. It can automatically load projects without manually restarting the spring boot application. During the development process, if we modify some java files, we may need to restart the project to view the modified results. If spring boot devtools is used, devtools will automatically restart the server for you when there are file changes in the classpath (Baidu.com’s introduction, in fact, you can customize the path according to your own situation).

First, look at the configuration information of devtools:

Because all automatic configurations of springboot are performed by xxxautoconfiguration, it is known that:

jetbrains://idea/navigate/reference?project=spring-boot-demo&path=~\.m2\repository\org\springframework\boot\spring-boot-devtools\2.6.4\spring-boot-devtools-2.6.4.jar!\org\springframework\boot\devtools\autoconfigure\RemoteDevToolsAutoConfiguration.class

is the automatic configuration class of devtools

This is for spring devtools. remote. Implementation of secret configuration.

View the process, first pass the values of secretheadername and ‘secret’ into the httpheaderaccessmanager class for processing:

Follow up httpheaderaccessmanager class:

In this class, a parameter HeaderName in the request header will be obtained for comparison. If the value of HeaderName is inconsistent with expectedsecret, 403 will be reported:

return RemoteDevToolsAutoConfiguration

Follow up DevToolsPropertiesclass see SecretHeaderName、Secret:

jetbrains://idea/navigate/reference?project=spring-boot-demo&path=~\.m2\repository\org\springframework\boot\spring-boot-devtools\2.6.4\spring-boot-devtools-2.6.4.jar!\org\springframework\boot\devtools\autoconfigure\DevToolsProperties.class

Follow up RemoteDevToolsProperties，in the getsecretheadername method,x-auth-token is returned, that is, the HTTP header has an x-auth-token header.

the x-auth-token value

getsecret is obtained from the configuration file:

Returning to remotedevtoolsaccessmanager, the httpheaderaccessmanager object returns the verification result of x-auth-token: Secret.

Continue to see vulnerabilities trigger key locations.

This part belongs to the remoterestartconfiguration static class, which is the devtools configuration implementation class:

View the remoterestarthandlermapper method

First, see to properties.getRemote(),follow up the devtoolsproperties class:

jetbrains://idea/navigate/reference?project=spring-boot-demo&path=~\.m2\repository\org\springframework\boot\spring-boot-devtools\2.6.4\spring-boot-devtools-2.6.4.jar!\org\springframework\boot\devtools\autoconfigure\DevToolsProperties.class

The getremote method returns the remotedevtoolsproperties object

Follow up remotedevtoolsproperties object
This class returns various corresponding property values:

The getcontextpath method returns the URL in the remoterestarthandlermapper method:

The URL is /~~ spring-boot!~/ restart.
Then continue to watch httprestartserverhandler

Follow up HttpRestartServer class:

In this class’s Handle method, obtain the request encapsulated as ObjectInputStream object, and then use ObjectInputStream’s ReadObject method,since the request is controllable, the vulnerability is formed.

Verify it：

 

Construct the request based on the analysis:

Text

POST /.~~spring-boot!~/restart 
HOST: 127.0.0.1
X-AUTH-TOKEN: The value here is the user-defined password in the configuration file. According to the use tutorial of devtools, it is found that most of them are mysecret and secret(default password, weak password). If you don't know the password, you can use script to guess the password. According to the previous analysis, if the password is wrong, it will report 403.  If the password is right, you will report an error when entering deserialization, so it will be prompted 500. You can guess the password according to these two mistakes.

Dependency:

Text

<dependency>
 <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
    <scope>runtime</scope>
    <optional>true</optional>
</dependency>

idea will import 2.6.4

Enable remote hot deployment in normal configuration
application.yml configuration：

Text

spring:
  devtools:
    restart:
      enabled: false  #Set hot deployment
      additional-paths: src/main/java #Restart directory
      exclude: WEB-INF/**
    remote:
      secret: mysecret

pom.xml configuration：：

Text

 <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
<!-- Set to include devtools when packaging the project. If set to true, devtools -- > will not be enabled after packaging the project-->
                    <excludeDevtools>false</excludeDevtools>
                </configuration>
            </plugin>

There will be a prompt after the project is started

use python writes a PoC to send data

Send the serialized malicious data to the target to trigger:

I found the vulnerability and contacted the spring, but the spring thought they explained the problem in the document, and suggested that the developer change <excludedevtools> false </excludedevtools> to true before releasing the formal environment, so that the production environment will not enable devtools, so it is not a vulnerability.

But I still think this is a risk. I suggest rewriting resolveclass and setting a deserialized object type of white list to avoid malicious deserialization.