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Fri, 09 Mar 2007:

In the dim dark past of October 2005, spo0nman and teemus did a hack in office. It was a tiny bit of javascript magic combined with a lot of heavy PNG maps and individually marking each cube's position on the map. It was the beginning of so many other nights when we did hacks - even weekends. But that's irrelevant. What is relevant is that to avoid slashdotting my puny little desktop, we had to distribute our load across all the machines - someone asked me to explain how we did that, quite recently and it needs a quick mention outside at least.

RewriteMap: Introducing to you, a small bit of hidden magic inside the apache mod_rewrite module - something which gets just a passing mention in the manual. You can define a RewriteMap which is a program - a full fledged script in any language you please.

RewriteMap    lb      prg:/usr/local/bin/lb.pl

RewriteRule   ^/floors/(\?.*)?$ ${lb:$1}  [R]

The script is not invoked for every request, but an instance of the script is kept alive and feed one line at a time. And because spo0nman wrote it, it ended up being a perl script. Here's the entire perl code.

#!/usr/bin/perl -w

$| = 1;

my @urls = qw (http://m1 http://m2 ...)

$cnt = 0;
while () {
        $cnt = (($cnt+1) % 3);
        my $mirror = $urls[$cnt];
        print "$mirror\n";

Now, the beauty of this is not in this code. The perl real beauty that came out of this was something which generates and rewrites dynamically without restarting apache - with a db or just about any data source you can code up.

Imagine a script which watches your access log to accumulate statistics. Now combine that with a script which wget's frequently hit URLs into a local file. And then imagine a perl script which does a stat() on that file and does an internal redirect to static pages if the file is recent enough (blog archives *cough*).

Implementing something like this into S9Y would make a lot of sense - the gain of hitting a static file would be a LOT better than using something like APC. Would make sense for someone like lunatech who still gets heavy hits on his comment disallowed archives but still uses php to serve out the pages (at least, they seem static, yet send out a X-Blog: Serendipity header). And rather than statically rendering all the pages (like I do), a hack like this could let you do only pages which get n+ requests per day or something and clean up on a cron with stat.atime values.

Hope someone reads this blog and saves me all that work ;)

Nothing is impossible for the man who doesn't have to do it himself.
                -- A.H. Weiler

posted at: 07:44 | path: /hacks | permalink | Tags: , ,

Being a psuedo-security guy of sorts, I'd decided to jump back into insecurity land a couple of weeks back. I haven't really been into security-tech for quite a long time, having hung up my script kiddie slingshot a long time back. But of late, it has again started to look attractive - but more than mere implementation issues, I've been looking for true blue design issues.

Recently on IRC, dumbhead was defending his default password on his router, which is conveniently firewalled off from the WAN. In my attempts to prove that setup insecure, I discovered DNS Pinning. It has been truly enlightening to perform a cursory attack on a home router with a faked up nameserver (re-used my twisted.names code).

The first request immediately does an iframe with a made-up hostname to ensure that no dns caches interfere. The resolution of that host (say "mordor") looks somewhat like this.

;mordor.                     IN      A

mordor.              284     IN      A       xxx.xxx.xx.xx
mordor.              284     IN      A

Now there is a good probability that the first IP will be hit nearly immediately by the browser. The server is running a script which tails the access log as soon as that vhost is hit (for dynamic vhosts, install lighttpd-mod-mysql-vhost), marking the vhost in the table as "hit". A sudo'd python script hooks into the mysql table, flips that flag to "block" after running an iptables packet drop on dst port 80, src ip of the victim.

Thirty seconds after loading the first iframe, the code in there creates another iframe with src=document.location+"?xyz". Very soon, that frame loads up in the same domain as the attacking website. I've got a default exploit sequence, which opens up port 22 for the Huawei WA1003A router which BSNL is distributing these days - but this requires the default password to be unchanged.

But the default password might not be required with the more expensive routers. If I could run my first evil iframe on port 2869 to commit the b0rkage, I would essentially be able to access the UPnP which takes a bit of SOAP to reduce the NAT into swiss cheese. But I'm a bit too lazy to actually write out those SOAP calls using XmlHttp (hah, same domain). And all that *without* a single password.

Most people have dismissed the DNS feature as unusable for hacking most websites because it sends invalid Host: headers and without cookies. But none of the routers I've looked at so far care about that or even have javascript checks for iframes (not that it will affect XHR much).

Amazingly simple, elegant. And DNS has been around for only 20 years ...

PS: thanks for providing the domain - you know who you are :)

The Domain Name Server (DNS) is the Achilles heel of the Web.
                      -- Sir Tim Berners-Lee

posted at: 04:23 | path: /insecurity | permalink | Tags: , ,