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Date: Thu, 13 Apr 2017 08:32:38 +0200
From: Andrej Nemec <>
Subject: Re: CVE Request - XStream: DoS when unmarshalling void

Hello Jörg,

Unfortunately, CVE assignments are not done through this list anymore.
You need to visit [1] and request a CVE by filing out the form. Could
you please look at it and let the list know about the assigned CVE?


Best Regards,


Andrej Nemec, Red Hat Product Security
3701 3214 E472 A9C3 EFBE 8A63 8904 44A1 D57B 6DDA

On 04/03/2017 01:55 PM, Jörg Schaible wrote:
> Hello,
> XStream is a Java library basically to marshal Java objects into XML and 
> back.
> Huawei engineers reported a reproducible crash of the Java VM (DoS) feeding 
> XStream with a specially crafted XML (note, that Stream also supports JSON, 
> that one can be used equally).
> Issue Description
> =================
> The processed stream at unmarshalling type contains type information to 
> recreate the formerly written objects. XStream creates therefore new 
> instances based on these type information. The crash occurrs if this 
> information advices XStream to create an instance of the primitive type 
> 'void'. This situation can only happen if an attacker was able to manipulate 
> the incoming data, since such an instance does not exist.
> Steps to Reproduce:
> ===================
> The simplest way to demonstrate the problem is with this snippet:
> XStream xstream = new XStream();
> xstream.fromXML("<void/>");
> If XStream is configured to read JSON, the equivalent line is:
> xstream.fromXML("{'void':null}");
> However, the problematic type information can be injected at any position in 
> the provided stream, in XML just by adding a class attribute:
> xstream.fromXML("<string class='void'>Hello, world!</string>");
> Impact:
> =======
> The vulnerability may allow a remote attacker to cause a crash on the target 
> system resulting in a denial of service only by manipulating the processed 
> input stream.
> Affected Versions:
> ==================
> Currently all versions until and including version 1.4.9 are affected, but 
> workarounds exist.
> Workarounds:
> ============
> XStream contains since version 1.4.7 a security framework to prevent an 
> attack described in CVE-2013-7285. This framework can also be used to 
> suppress the current vulnerability by setting:
> xstream.denyTypes(void.class, Void.class);
> Users of older XStream releases can register an own converter for the 'void' 
> type, that also protects against this attack:
> xstream.registerConverter(new Converter() {
>   public boolean canConvert(Class type) {
>     return Void.class == type || void.class == type;
>   }
>   public Object unmarshal(HierarchicalStreamReader reader, 
> UnmarshallingContext context) {
>     throw new ConversionException("Type void cannot have an instance");
>   }
>   public void marshal(Object source, HierarchicalStreamWriter writer, 
> MarshallingContext context) {
>     throw new ConversionException("Type void cannot have an instance");
>   }
> Regards,
> Jörg Schaible
> Maintainer of XStream.

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