Re: Webmin miniserv.pl format string vulnerability

[Dave Aitel <dave () immunitysec com>]

It's definitely possible. I threw up Bas's efforts into Immunity 
Partner's a few minutes ago. Bas has the flu, or he'd respond, but we 
did all our testing on Suse 9.3 so far, I believe.

In other words: Jack is not full of it. :>

Thanks,
Dave Aitel
Immunity, Inc.

H D Moore wrote:
> On Tuesday 29 November 2005 04:07, advisory () dyadsecurity com wrote:
>   
> > [snip ] so so if remote code execution is successful, it would
> > lead to a full remote root compromise in a standard configuration. 
> >     
>
>   
> > DESCRIPTION.  The username parameter of the login form is logged via
> > the perl `syslog' facility in an unsafe manner during a unknown user
> > login attempt. the perl syslog facility passes the username on to the
> > variable argument function sprintf that will treat any format
> > specifiers and process them accordingly.
> >
> > DETAILS.  The vectors for a simple DoS of the web server are to use the
> > %n and %0(large number)d inside of the username parameter, with the
> > former causing a write protection fault within perl leading to script
> > abortion, and the latter causing a large amount of memory to be
> > allocated inside of the perl process.
> >     
>
> Sys::Syslog calls sprintf($format, @_). I tried testing this on perl 5.8.7 
> and don't see how this can be exploitable.  The %n specifier results in 
> the following error message:
>
> $ perl -e 'sprintf("%n")'
> Modification of a read-only value attempted at -e line 1.
>
> Using a thousand %p's results in the same address (presumably of the 
> temporary char *) over and over again
>
> It is possible to memory starve webmin with a long %9999999999d string, 
> but arbitrary memory writes seem to be out of the question.
>
> What version of perl was used by the third-party to exploit this?
>
> Does anyone else have experience exploiting sprintf() calls in the perl 
> interpreter?
>
> -HD
>