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From robert burrell donkin <>
Subject RE: [logging] tech.xml - child-first classloading not consideredharmful
Date Wed, 04 May 2005 21:33:14 GMT
the setup i had in mind was a container with a buggy classloader. the
security manager would allow classloaders to be created by the container
but try to prevent access to certain files. the malicious web
application code would be crafted to exploit the bug in the container
classloader to allow a malicious SecurityManager to be loaded which
would then allow those file to be read. 

- robert
On Wed, 2005-05-04 at 16:41 -0400, James Carman wrote:
> If a security manager was in place to begin with, which it would be in an
> environment which you would want to secure, it probably wouldn't allow
> applications to create their own classloaders anyway (the ClassLoader class'
> constructor checks to see whether you have that privilege).  A reasonable
> SecurityManager wouldn't allow itself to be replaced, so a "malicious" one
> wouldn't be able to let an application "break out of its sandbox."  If there
> isn't a SecurityManager installed, there IS no sandbox.
> -----Original Message-----
> From: robert burrell donkin [] 
> Sent: Wednesday, May 04, 2005 4:39 PM
> To: Jakarta Commons Developers List
> Subject: Re: [logging] tech.xml - child-first classloading not
> consideredharmful
> On Wed, 2005-05-04 at 13:03 -0700, Mike Colbert wrote:
> > > in the case of a parent-first classloader, the buggy implementation 
> > > would not be exposed since the call would be delegated to the system 
> > > classloader. in the case of a child-first classloader, a buggy 
> > > implementation may try to define SecurityManager itself and this bug 
> > > exploited.
> > 
> > This would mean an attacker would have to take advantage of a bug in a 
> > class loader which allows them to load a malicious SecurityManager in 
> > such a way that it would be shared by all applications.  I can kind of 
> > see how parent-first delegation would mitigate this, but one would 
> > think that with appropriate levels of class loader isolation in place 
> > the delegation order becomes a non-issue.  Maybe the bug has something 
> > to do with broken isolation.
> i was thinking that a malicious SecurityManager implementation might allow
> an application to break out of it's sandbox but i'm not an expert and this
> is really just speculation on my part. i don't think that this kind of
> attack is any sort of realistic threat. this would be a good time for craig
> to jump in...
> - robert
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