This document discusses Java deserialization vulnerabilities. It provides an introduction to how Java serialization works and what the security issues are. Specifically, it describes how an attacker can exploit vulnerabilities to remotely execute code on a server by deserializing malicious objects. The document gives examples of past vulnerabilities found in various Java applications and frameworks. It also provides tips for finding vulnerabilities and generating payloads to demonstrate exploits.
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Java Deserialization Vulnerabilities - The Forgotten Bug Class
2. About me
Head of Vulnerability Research at Code White in Ulm, Germany
Specialized on (server-side) Java
Found bugs in products of Oracle, VMware, IBM, SAP, Symantec, Apache, Adobe, etc.
Recently looking more into the Windows world and client-side stuff
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@matthias_kaiser
3. Agenda
Introduction
Java’s Object Serialization
What’s the problem with it
A history of bugs
Finding and exploiting
Code White’s bug parade + a gift for Infiltrate
More to come?
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4. Should you care?
If your client is running server products of
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you SHOULD!
5. Some facts
The bug class exists for more than 10 years
Most ignored bug class in the server-side Java world until 2015
A easy way to get reliable RCE on a server
Architecture independent exploitation
With Java deserialization vulnerabilities you can pwn a corp easily!
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6. Where is it used
Several J2EE/JEE core technologies rely on serialization
Remote Method Invocation (RMI)
Java Management Extension (JMX)
Java Message Service (JMS)
Java Server Faces implementations (ViewState)
Communication between JVMs in general (because devs are lazy :-)
Custom application protocols running on top of http, etc.
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8. Overview of Java’s Object Serialization Protocol
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Magic
class name
field type
class field
Class description info
TC_OBJECT
TC_CLASSDESC
classdata[]
9. There is protocol spec and a grammar
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https://docs.oracle.com/javase/8/docs/platform/serialization/spec/protocol.html
11. What’s the problem
ObjectInputStream doesn’t include validation features in its API
All serializable classes that the current classloader can locate and load can get deserialized
Although a class cast exception might occur in the end, the object will be created!
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12. What’s the problem #2
A developer can customize the (de)-serialization of a serializable class
Implement methods writeObject(), writeReplace(), readObject() and readResolve()
ObjectInputStream invokes readObject() and readResolve()
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Under our control!
13. What’s the problem #3
Further methods can be triggered by using certain classes as a "trampoline"
Object.toString() using e.g. javax.management.BadAttributeValueExpException
Object.hashCode() using e.g. java.util.HashMap
Comparator.compare() using e.g. java.util.PriorityQueue
etc.
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Trampoline
class
Target
class
14. What’s the problem #3
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javax.management.BadAttributeValueExpException
1. Reading the field "val"
2. Calling "toString()" on "val"
15. History of Java deserialization vulnerabilities
JRE vulnerabilities
(DoS)
Marc Schönefeld
2006
JSF Viewstate
XSS/DoS
Sun Java Web Console
Luca Carretoni
2008
CVE-2011-2894
Spring Framework RCE
Wouter Coekaerts
CVE-2012-4858
IBM Cognos Business
Intelligence RCE
Pierre Ernst
2011 2012
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16. History of Java deserialization vulnerabilities
CVE-2013-1768 Apache OpenJPA RCE
CVE-2013-1777 Apache Geronimo 3 RCE
CVE-2013-2186 Apache commons-fileupload RCE
Pierre Ernst
CVE-2015-3253 Groovy RCE
CVE-2015-7501 Commons-Collection RCE
Gabriel Lawrence and Chris Frohoff
CVE-2013-2165 JBoss RichFaces RCE
Takeshi Terada
2013 2015
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18. Finding is trivial
Use an IDE like Intellij or Eclipse and trace the call paths to ObjectInputStream.readObject()
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19. Exploitation
Exploitation requires a chain of serialized objects triggering interesting functionality e.g.
writing files
dynamic method calls using Java’s Reflection API
etc.
For such a chain the term "gadget" got established
Chris Frohoff and others found several gadgets in standard libs
Let’s look at an example gadget
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20. Javassist/Weld Gadget
Gadget utilizes JBoss’ Javassist and Weld framework
Reported to Oracle with the Weblogic T3 vulnerability
Works in Oracle Weblogic and JBoss EAP
Allows us to call a method on a deserialized object
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22. Javassist/Weld Gadget summary
During deserialization a "POST_ACTIVATE" interception will be executed
We can create an "interceptorHandlerInstances" that defines our deserialized target object as
a handler for a "POST_ACTIVATE" interception
We can create an "interceptionModel" that defines a method to be executed on our handler for
a "POST_ACTIVATE" interception
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25. "Return of the Rhino"-Gadget
Gadget utilizes Rhino Script Engine of Mozilla
Works with latest Rhino in the classpath
Oracle applied some hardening to its Rhino version
So only works Oracle JRE <= jre7u13
Works with latest openjdk7-JRE (e.g. on Debian, Ubuntu)
Allows us to call a method on a deserialized object
Will be released on our blog soon
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26. What to look for?
Look for methods in serializable classes
working on files
triggering reflection (invoking methods, getting/setting properties on beans)
doing native calls
etc.
AND being called from
readObject()
readResolve()
toString()
hashCode()
finalize()
any other method being called from a "Trampoline" class
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27. What to look for?
Look at serializable classes used in Java reflection proxies
java.lang.reflect.InvocationHandler implementations
javassist.util.proxy.MethodHandler implementations
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InvocationHandlerInterface
Proxy
toString() invoke (…) // do smth
invoke (target, toString, args)
28. What to look for?
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Prints out method being called
29. What to look for?
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What if InvocationHandler.invoke()
does "scary" things using values from
the serialized object input stream?
Proxy
30. Making gadget search easier
Chris Frohoff released a tool for finding gadgets using a graph database
Using object graph queries for gadget search
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31. Exploitation tricks
Adam Gowdiak’s TemplatesImpl
com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl is serializable
Allows to define new classes from your byte[ ][ ]
Calling TemplatesImpl.newTransformer() on deserialized object Code Execution
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32. Exploitation tricks
InitialContext.lookup()
@zerothoughts published a gadget in Spring’s JtaTransactionManager recently
Triggers InitialContext.lookup(jndiName)
Uses "rmi://yourFakeRmiServer/…" as jndiName
Loads classes from your fake RMI server
Calling JdbcRowSetImpl.execute() on a deserialized object will do the same
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33. Payload generation
Chris Frohoff released the great tool "ysoserial"
Makes creation of payloads easy
Includes gadgets for
Commons Collection 3 & 4
Spring
Groovy
JRE7 (<= jre7u21)
Commons BeanUtils
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34. Custom payloads
I wouldn’t go for Runtime.getRuntime().exec(cmd) for several reasons
Most of the gadgets don’t touch the disk
With scripting languages your life gets even easier
Use what’s in the classpath
Javascript (Rhino, Nashorn)
Groovy
Beanshell
etc.
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37. Oracle Weblogic
Oracle’s Application Server (acquired from BEA)
Middleware for core products of Oracle
Oracle Enterprise Manager
Oracle VM Manager
Oracle ESB
Oracle Hyperion
Oracle Peoplesoft
And many more
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38. CVE-2015-4852 - Oracle Weblogic
Reported on 21st of July 2015 to Oracle as "Oracle Weblogic T3 Deserialization Remote Code
Execution Vulnerability"
Detailed advisory with POCs
Using Chris Frohoff’s Commons Collection Gadget
Using my Javassist/Weld Gadget
I recommended to implement "Look-ahead Deserialization" by Pierre Ernst
Yeah, the one @foxglovesec dropped …
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39. CVE-2015-4852 - Oracle Weblogic
Weblogic uses multi-protocol listener architecture
Channels can be defined listening for several protocols
The "interesting" protocols are t3 and t3s
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40. CVE-2015-4852 - T3 Protocol
Weblogic has its own RMI protocol called T3
Exists since the early days of Weblogic
Used for JEE remoting (e.g. Session Beans)
Used for JMX (e.g. by Weblogic Scripting Tool)
Can also be tunneled over HTTP (if enabled)
Check http://target:port/bea_wls_internal/HTTPClntLogin/a.tun
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41. CVE-2015-4852 - How I found the bug
Found during my daughter’s midday nap ;-)
Remembered the time when I was Dev and writing software for NATO systems
We used to deploy software on Weblogic using T3
Just wrote some lines to create a T3 connection
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42. CVE-2015-4852 - How I found the bug
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I haven’t specified any user, right?
43. T3Client
CVE-2015-4852 - Oracle Weblogic
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1. Checking the protocol
2. Create "RJVM" object
4. Call a RMI method on
on the stub
3. Create a RMI stub
49. CVE-2015-4852 - Can it be fixed easily?
Fixing this doesn’t look easy, serialization is used in the core protocol
You can find a lot of gadgets in the classpath of Weblogic
Oracle "patched" it by implementing a check against a "blacklist"
Btw. there are other calls to readObject()
e.g. look at the code for "clustering" ;-)
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50. Infiltrate gift= 0day
Why always bashing Oracle
There is more enterprise software out there!
How about software from Germany?
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52. SAP Netweaver AS Intro
SAP has two Application Servers
SAP Netweaver AS ABAP
SAP Netweaver AS JAVA
SAP Netweaver AS JAVA is mainly used for
Portal
Process Integration (=ESB)
Solution Manager
BI (dual stacked system)
There are many open ports, starting from 50000
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55. SAP Netweaver AS Java - How I found the bug
It took more time to get a running version of Netweaver compared to finding the bug
Used a VM from SAP Cloud Appliance Library hosted on AWS
Same approach as with Oracle Weblogic
Looking for a client program and searching for ObjectOutputStream.writeObject()
Affects at least version 7.1, 7.2, 7.3 and 7.4
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56. SAP Netweaver AS Java - Exploiting the bug
Netweaver runs its own SAP JRE
Chris Frohoff’s universal JRE gadget works well
Tested with Netweaver AS Java 7.3 and 7.4, should work with 7.1 / 7.2
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59. More to come?
Sure! Bugs & Gadgets
I already mentioned that Java Messaging is using Serialization heavily
Currently I’m working on the Java Messaging Exploitation Tool (JMET)
Integrates Chris Frohoff’s ysoserial
Pwns your queues/topics like a boss!
Planned to be released around summer ‘16
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60. Conclusion
Java Deserialization is no rocket science
Finding bugs is trivial, exploitation takes more
So many products affected by it
Research has started, again …
This will never end!
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