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Last week we published fixes for flaws in libPNG found by a UK researcher. Since these flaws didn't get much press attention I wanted to take this opportunity to fill in a few of the details. If you don't want the details just goto https://rhn.redhat.com/cve/CAN-2004-0597.html and update your systems right now.

Chris Evans discovered a stack buffer overflow in the libPNG library. This means that an attacker could create a malicious PNG image file to take advantage of the flaw. If you were to view that malicious image on your system then it could execute arbitrary code as you. Since most applications that display PNG files are linked to libPNG or contain libPNG code, that increases the risk of this flaw.

Whilst researching affected applications we found that most browsers were affected - so an attacker would simply have to put a malicious image onto a web site that you visit. You'd still need to be forced to visit that web site though. Or maybe the attacker can act as a man-in-the-middle and inject the malicious image file (as was reported recently at DefCon where wireless surfers had all their images replaced). More worrying are perhaps email applications that might load images by default, which could allow propegation of a worm. This isn't an issue that only affects Linux; just sending malicious images in attachments to someone using AppleMail on MAC OSX is enough to trigger the flaw.

Although i've not yet seen an exploit containing shellcode for this issue we believe it is triviallly exploitable. This is a "Critical" update.

Red Hat Enterprise Linux users need to update their libpng and Mozilla (which contained it's own copy of libpng) packages. Updating libpng is sufficient to protect all the applications that use that library to decode images (although you'll need to restart any applications you've already got running to pick up the change, it's probably easiest just to restart your system if you're unsure).

Fedora Core users should be protected against possible exploits of this issue by exec-shield, but should still upgrade (as a malicious PNG file would still crash an application).

https://rhn.redhat.com/cve/CAN-2004-0597.html

Because libpng is under a BSD-style license, anyone is basically free to use or include libpng even in closed-source products. So expect to see a whole raft of advisories over the coming weeks as other vendors come to discover that they're vulnerable to this issue.


So according to a Secunia advisory I just read there is a new flaw in Apache that allows attackers to "compromise a vulnerable system". [source]

They got that information from a Connectiva security advisory. That advisory actually says "trigger the execution of arbitrary commands" but if you read the context you'll find that in fact what it means is that a cunning attacker could use a minor flaw in Apache that allows it to log escape characters in order to exploit possible flaws in terminal emulators to execure arbitrary commands if you view the log file. [source].

So we've magically turned an issue which is of quite minor risk and minor severity into one classed as "Moderately Critical". Using the same logic you could then use publicised (but fixed) flaws in the Linux kernel to gain root privileges and we've got a remote root exploit in Apache folks! It's Chinese Whisper Security Advisories at their best.


So our joint statement in response to the Forrester Study is now available and it got to slashdot and other places. It should be an identical statement from each vendors site - although I think the European -ise's got replaced with -ize's in some of the statements. It's quite an event to have four competing Linux distributions giving a joint statement on an issue - but behind the scenes this goes on all the time. Every day we work with our competitors in the other Linux vendor security teams to make sure that Linux users get quality, peer-reviewed, security fixes in a timely fashion.


What a busy day; doing the OpenSSL release manager role for the recent security updates, testing packages, dealing with the third parties, being a third party, rolling, pushing, correcting.

What is disturbing is a report from a third party company who is vulnerable to one of the Denial of service issues that said that it wasn't a security issue as their were hundreds of other possible DoS attacks. Actually, this attack causes OpenSSL to crash. We've got a proof of concept, you don't have to send more than a kb of data to get OpenSSL to crash remotely. This can be quite serious if you have a service that can't recover from that. Things like Apache (when running in its default prefork memory model) can recover quite well - they just spawn off a new child to replace the dead one. This is going to use up some extra resources, but depending on the platform it's quite minor (and will stop as soon as the attacker stops sending malicious packets). Not everything that listens to the network that uses OpenSSL is so resiliant.

Going to be in London next weekend?


As I was commiting the template for this weeks issue of Apache Week I noticed that it has now been exactly eight years since I wrote the first issue. Back then Apache wasn't so popular and the documentation was lacking. Apache Week was designed specifically to give administrators the confidence to try the Apache web server on their machines without having to parse the hundreds of messages each week on the developer mailing list. That first issue was written over a 64k ISDN dial-up line from a computer perched on stark IKEA tabletop. Friday afternoons were spent writing up what had happened during the week. Not much has changed. Actually, I think that IKEA tabletop is still sitting in storage somewhere at Red Hat in Guildford. I wish I'd kept hold of it, it would have been useful for my girlfriends sons train layout.

Over the years there have been many times when we've thought about stopping production, usually when a competitor announced some other Apache magazine that we thought would do a better job than we do. But most of them gave up. They probably realised that there wasn't any money to be made from an Apache httpd journal.

UK Web became C2Net which became Red Hat, and Apache Week is still going strong. We'll have to think of something exciting to do for our tenth birthday.


My paper on "Security Response and Vendor Accountability for Open Source Software" was accepted for Linux World 2003 in San Francisco and I'm giving a similar talk at Linux for Business in London on the 10th June. The role of the open source vendor is often neglected when folks talk about the security of open source software.

House modifications are coming along well, with updates to the Home Automation security software (a few suprises for any intruder), and some large black marble balls on a rockery out the front. Tracy has been spending a few days pressure-washing the driveway which is fun apart from the occasional lump of sand that gets blasted at random parts of your body. Sand in your nose is quite annoying.


Had an interesting week wading through vulnerability details and the various advisories which never really seem to match the facts. Take one Linux vendor for example who got confused about the Oracle mod_dav vulnerability and, even though they were not affected by the vulnerability, released new Apache mod_dav packages. To add to the confusion their newly released errata packages had actually added a patch which added in the vulnerability. So they started out not vulnerable, but then released a patch which was meant to remove the vulnerability but actually really made them vulnerable. No wonder folks are confused. Wrote a bit of a rant about it in Apache Week this week.


What a busy couple of days. It all started last month with a seemingly innocent DOS being reported to the Apache security team. jorton and I spent some time analysing it and found that although it wasn't exploitable on 32 bit until platforms it may well be exploitable on some 64 bit machines. Then started the co- ordination work with CERT.

Then, suddenly, the ISS team announced the same issue publically causing us to go into firefighting mode and release the advisory (which I'd fortunately already drafted and got positive feedback on), followed by seemingly hundreds of press calls, lots of additional analysis, and reading ISS say I was untrustworthy in some Chicago newspaper ;-)

Now for some sleep


Several hours later and I manage to find out the extended commands for the LW11G dimmer unit. Can't find these anywhere else mentioned on the web, so for future generations:

# Extended X10 control of LW11G dimmer
#
# Unlike other L*11* modules the LW11G
# seems to only respond to code 53.  Set the data to
#
# 0 = immediate off
# 255 = immediate on
# 1-254 = slowly dim or bright to that level, turns on if
not already


A discussion about XML status output in Apache came up this week and so I pointed out a mod_status_xml I wrote a month or two ago. It would be great to get something like this module (or a patch to mod_status) into the core as once you can get XML status output you can do all sorts of cool things like historic graphs, real time graphs, and so on. Kind of like the stuff from 1995 that graphed server status but now using SVG.

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Hi! I'm Mark Cox. This blog gives my thoughts and opinions on my security work, open source, fedora, home automation, and other topics.