Monday, March 03, 2008

Die Hard: disabling snmpXdmid on Solaris 10 (dmi)

On a recent server build project we ran into a security scan that surprised us with a mandate that snmpXdmid be disabled. The alleged vulnerability is based on a buffer overflow that originated in the days of Solaris 8 as documented in CIAC Information Bulleting l-065 and SunSolve Security bulletin #00207. The details aren't important to this story other than finding it entertaining to respond to a Solaris 8 vulnerability on a Solaris 10 build. I'll save my thoughts on the corporate world's implementation of automated scanning for another post.

Our normal JumpStart image was configured about a year and a half ago, and in it we addressed the problem. Of course, none of us could remember what we did, and it turns out to not be the easiest thing to extract from Google. The process is pretty straight forward once you find it...

# svcadm disable dmi

Next, I dug up a quick test case to make sure the fix worked. It's easy enough to check registered RPC services using rpcinfo.

# rpcinfo -p | grep 100249
100249 1 udp 43483
100249 1 tcp 42683

Wait a minute... I thought I turned that off! The normal behavior of the service management facility, or SMF is to immediately change the state of a service after a disable command, so I made the (false) assumption that I had disabled the wrong service. After some additional research and testing I found that I wasn't wrong. The SMF was wrong. I did a quick zone reboot, and sure enough, the service was no longer responding. This led me to conclude the DMI service was not removing its registration with the portmapper (svc:/network/rpc/bind:default).

The next step on the path is to look at the service method that stops and starts the DMI service. All method scripts are stored in /lib/svc/method, and this one is easy to find: svc-dmi. So now we need to take a look at how it goes about stopping the service:

/usr/bin/pkill -9 -x -u 0 -z ${_INIT_ZONENAME:=`/sbin/zonename`} \

And so we come to the flaw in this method. In order to be consistent with predominant SMF behavior, this method should stop the service completely. There are two ways we can address this. We can either restart the entire portmapper, or we can be more surgical and remove the snmpXdmid registration from the portmapper. I preferred the latter since restarting the portmapper could temporarily impact other services. the code change is pretty simple:

/usr/bin/pkill -9 -x -u 0 -z ${_INIT_ZONENAME:=`/sbin/zonename`} \
'(snmpXdmid|dmispd)' && /usr/bin/rpcinfo -d 100249 1

The problem, of course, is that to implement this fix I need to modify a script which is managed by the pkgadd facility, and subsequently, checksummed. I wont' get into addressing that issue right now, as the goal of this post is simply to provide breadcrumbs to other Jedi working to improve security with as little impact as possible.


MuthuSelvan said...
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Mark said...

god bless you!