Over the past few years TCP sequence number prediction attacks have become a
real threat against unprotected networks, taking advantage of the inherent
trust relationships present in many network installations. TCP sequence
number prediction attacks have most commonly been implemented by opening a
series of connections to the target host, and attempting to predict the
sequence number which will be used next. Many operating systems have
therefore attempted to solve this problem by implementing a method of
generating sequence numbers in unpredictable fashions. This method does
not solve the problem.
This advisory introduces an alternative method of obtaining the initial
sequence number from some common trusted services. The attack presented here
does not require the attacker to open multiple connections, or flood a port
on the trusted host to complete the attack. The only requirement is that
source routed packets can be injected into the target network with fake
source addresses.
This advisory assumes that the reader already has an understanding of how
TCP sequence number prediction attacks are implemented.
The impact of this advisory is greatly diminished due to the large number of
organizations which block source routed packets and packets with addresses
inside of their networks. Therefore we present the information as more of
a 'heads up' message for the technically inclined, and to re-iterate that
the randomization of TCP sequence numbers is not an effective solution
against this attack.
Technical Details
~~~~~~~~~~~~~~~~~
The problem occurs when particular network daemons accept connections
with source routing enabled, and proceed to disable any source routing
options on the connection. The connection is allowed to continue, however
the reverse route is no longer used. An example attack can launched against
the in.rshd daemon, which on most systems will retrieve the socket options
via getsockopt() and then turn off any dangerous options via setsockopt().
An example attack follows.
Host A is the trusted host
Host B is the target host
Host C is the attacker
Host C initiates a source routed connection to in.rshd on host B, pretending
to be host A.
Host C spoofing Host A <SYN> --> Host B in.rshd
Host B receives the initial SYN packet, creates a new PCB (protocol
control block) and associates the route with the PCB. Host B responds,
using the reverse route, sending back a SYN/ACK with the sequence number.
Host C spoofing Host A <-- <SYN/ACK> Host B in.rshd
Host C responds, still spoofing host A, acknowledging the sequence number.
Source routing options are not required on this packet.
Host C spoofing Host A <ACK> --> Host B in.rshd
We now have an established connection, the accept() call completes, and
control is now passed to the in.rshd daemon. The daemon now does IP
options checking and determines that we have initiated a source routed
connection. The daemon now turns off this option, and any packets sent
thereafter will be sent to the real host A, no longer using the reverse
route which we have specified. Normally this would be safe, however the
attacking host now knows what the next sequence number will be. Knowing
this sequence number, we can now send a spoofed packet without the source
routing options enabled, pretending to originate from Host A, and our
command will be executed.
In some conditions the flooding of a port on the real host A is required
if larger ammounts of data are sent, to prevent the real host A from
responding with an RST. This is not required in most cases when performing
this attack against in.rshd due to the small ammount of data transmitted.
It should be noted that the sequence number is obtained before accept()
has returned and that this cannot be prevented without turning off source
routing in the kernel.
As a side note, we're very lucky that TCP only associates a source route with
a PCB when the initial SYN is received. If it accepted and changed the ip
options at any point during a connection, more exotic attacks may be possible.
These could include hijacking connections across the internet without playing
a man in the middle attack and being able to bypass IP options checking
imposed by daemons using getsockopt(). Luckily *BSD based TCP/IP stacks will
not do this, however it would be interesting to examine other implementations.
Impact
~~~~~~
The impact of this attack is similar to the more complex TCP sequence
number prediction attack, yet it involves fewer steps, and does not require
us to 'guess' the sequence number. This allows an attacker to execute
arbitrary commands as root, depending on the configuration of the target
system. It is required that trust is present here, as an example, the use
of .rhosts or hosts.equiv files.
Solutions
~~~~~~~~~
The ideal solution to this problem is to have any services which rely on
IP based authentication drop the connection completely when initially
detecting that source routed options are present. Network administrators
and users can take precautions to prevent users outside of their network
from taking advantage of this problem. The solutions are hopefully already
either implemented or being implemented.
1. Block any source routed connections into your networks
2. Block any packets with internal based address from entering your network.
Network administrators should be aware that these attacks can easily be
launched from behind filtering routers and firewalls. Internet service
providers and corporations should ensure that internal users cannot launch
the described attacks. The precautions suggested above should be implemented
to protect internal networks.
Example code to correctly process source routed packets is presented here
as an example. Please let us know if there are any problems with it.
This code has been tested on BSD based operating systems.
u_char optbuf[BUFSIZ/3];
int optsize = sizeof(optbuf), ipproto, i;
struct protoent *ip;
if ((ip = getprotobyname("ip")) != NULL)
ipproto = ip->p_proto;
else
ipproto = IPPROTO_IP;
if (!getsockopt(0, ipproto, IP_OPTIONS, (char *)optbuf, &optsize) &&
optsize != 0) {
for (i = 0; i < optsize; ) {
u_char c = optbuf[i];
if (c == IPOPT_LSRR || c == IPOPT_SSRR)
exit(1);
if (c == IPOPT_EOL)
break;
i += (c == IPOPT_NOP) ? 1 : optbuf[i+1];
}
}
One critical concern is in the case where TCP wrappers are being used. If
a user is relying on TCP wrappers, the above fix should be incorporated into
fix_options.c. The problem being that TCP wrappers itself does not close
the connection, however removes the options via setsockopt(). In this case
when control is passed to in.rshd, it will never see any options present,
and the connection will remain open (even if in.rshd has the above patch
incorporated). An option to completely drop source routed connections will
hopefully be provided in the next release of TCP wrappers. The other option
is to undefine KILL_IP_OPTIONS, which appears to be undefined by default.
This passes through IP options and allows the called daemon to handle them
accordingly.
Disabling Source Routing
~~~~~~~~~~~~~~~~~~~~~~~~
We believe the following information to be accurate, however it is not
guaranteed.
--- Cisco
To have the router discard any datagram containing an IP source route option
issue the following command:
no ip source-route
This is a global configuration option.
--- NetBSD
Versions of NetBSD prior to 1.2 did not provide the capability for disabling
source routing. Other versions ship with source routing ENABLED by default.
We do not know of a way to prevent NetBSD from accepting source routed packets.
NetBSD systems, however, can be configured to prevent the forwarding of packets
when acting as a gateway.
To determine whether forwarding of source routed packets is enabled,
issue the following command:
# sysctl net.inet.ip.forwarding
# sysctl net.inet.ip.forwsrcrt
The response will be either 0 or 1, 0 meaning off, and 1 meaning it is on.
Forwarding of source routed packets can be turned off via:
# sysctl -w net.inet.ip.forwsrcrt=0
Forwarding of all packets in general can turned off via:
# sysctl -w net.inet.ip.forwarding=0
--- BSD/OS
BSDI has made a patch availible for rshd, rlogind, tcpd and nfsd. This
patch is availible at:
ftp://ftp.bsdi.com/bsdi/patches/patches-2.1
OR via their patches email server <patches@bsdi.com>
The patch number is
U210-037 (normal version)
D210-037 (domestic version for sites running kerberized version)
BSD/OS 2.1 has source routing disabled by default
Previous versions ship with source routing ENABLED by default. As far as
we know, BSD/OS cannot be configured to drop source routed packets destined
for itself, however can be configured to prevent the forwarding of such
packets when acting as a gateway.
To determine whether forwarding of source routed packets is enabled,
issue the following command:
# sysctl net.inet.ip.forwarding
# sysctl net.inet.ip.forwsrcrt
The response will be either 0 or 1, 0 meaning off, and 1 meaning it is on.
Forwarding of source routed packets can be turned off via:
# sysctl -w net.inet.ip.forwsrcrt=0
Forwarding of all packets in general can turned off via:
# sysctl -w net.inet.ip.forwarding=0
--- OpenBSD
Ships with source routing turned off by default. To determine whether source
routing is enabled, the following command can be issued:
# sysctl net.inet.ip.sourceroute
The response will be either 0 or 1, 0 meaning that source routing is off,
and 1 meaning it is on. If source routing has been turned on, turn off via:
# sysctl -w net.inet.ip.sourceroute=0
This will prevent OpenBSD from forwarding and accepting any source routed
packets.
--- FreeBSD
Ships with source routing turned off by default. To determine whether source
routing is enabled, the following command can be issued:
# sysctl net.inet.ip.sourceroute
The response will be either 0 or 1, 0 meaning that source routing is off,
and 1 meaning it is on. If source routing has been turned on, turn off via:
# sysctl -w net.inet.ip.sourceroute=0
--- Linux
Linux by default has source routing disabled in the kernel.
--- Solaris 2.x
Ships with source routing enabled by default. Solaris 2.5.1 is one of the
few commercial operating systems that does have unpredictable sequence
numbers, which does not help in this attack.
We know of no method to prevent Solaris from accepting source routed
connections, however, Solaris systems acting as gateways can be prevented
from forwarding any source routed packets via the following commands:
# ndd -set /dev/ip ip_forward_src_routed 0
You can prevent forwarding of all packets via:
# ndd -set /dev/ip ip_forwarding 0
These commands can be added to /etc/rc2.d/S69inet to take effect at bootup.
--- SunOS 4.x
We know of no method to prevent SunOS from accepting source routed
connections, however a patch is availible to prevent SunOS systems from
forwarding source routed packets.
This patch is availible at:
ftp://ftp.secnet.com/pub/patches/source-routing-patch.tar.gz
To configure SunOS to prevent forwarding of all packets, the following
command can be issued:
# echo "ip_forwarding/w 0" | adb -k -w /vmunix /dev/mem
# echo "ip_forwarding?w 0" | adb -k -w /vmunix /dev/mem
The first command turns off packet forwarding in /dev/mem, the second in
/vmunix.
--- HP-UX
HP-UX does not appear to have options for configuring an HP-UX system to
prevent accepting or forwarding of source routed packets. HP-UX has IP
forwarding turned on by default and should be turned off if acting as a
firewall. To determine whether IP forwarding is currently on, the following
command can be issued:
# adb /hp-ux
ipforwarding?X <- user input
ipforwarding:
ipforwarding: 1
#
A response of 1 indicates IP forwarding is ON, 0 indicates off. HP-UX can
be configured to prevent the forwarding of any packets via the following
commands:
# adb -w /hp-ux /dev/kmem
ipforwarding/W 0
ipforwarding?W 0
^D
#
--- AIX
AIX cannot be configured to discard source routed packets destined for itself,
however can be configured to prevent the forwarding of source routed packets.
IP forwarding and forwarding of source routed packets specifically can be
turned off under AIX via the following commands:
To turn off forwarding of all packets:
# /usr/sbin/no -o ipforwarding=0
To turn off forwarding of source routed packets:
# /usr/sbin/no -o nonlocsrcroute=0
Note that these commands should be added to /etc/rc.net
If shutting off source routing is not possible and you are still using
services which rely on IP address authentication, they should be disabled
immediately (in.rshd, in.rlogind). in.rlogind is safe if .rhosts and
/etc/hosts.equiv are not used.
Attributions
~~~~~~~~~~~~
Thanks to Niels Provos <provos@physnet.uni-hamburg.de> for providing
the information and details of this attack. You can view his web
site at http://www.physnet.uni-hamburg.de/provos
Thanks to Theo de Raadt, the maintainer of OpenBSD for forwarding this
information to us. More information on OpenBSD can be found at
http://www.openbsd.org
Thanks to Keith Bostic <bostic@bsdi.com> for discussion and a quick
solution for BSD/OS.
Thanks to Brad Powell <brad.powell@west.sun.com> for providing information
for Solaris 2.x and SunOS 4.x operating systems.
Thanks go to CERT and AUSCERT for recommendations in this advisory.
You can contact the author of this advisory at oliver@secnet.com
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Copyright Notice
~~~~~~~~~~~~~~~~
The contents of this advisory are Copyright (C) 1997 Secure Networks Inc,
and may be distributed freely provided that no fee is charged for
distribution, and that proper credit is given.
You can find Secure Networks papers at ftp://ftp.secnet.com/pub/papers
and advisories at ftp://ftp.secnet.com/advisories
You can browse our web site at http://www.secnet.com
You can subscribe to our security advisory mailing list by sending mail to
majordomo@secnet.com with the line "subscribe sni-advisories"
accordion menu or extend the following way installation,
this menu from the abu Farhan
example:
you try to click on a category below
This script:
<script src="http://abu-farhan.com/script/acctoc/daftarisiv2-pack.js">Replace http://Your-Link.com/ with your link,.
</script>
<script src="http://Your-Link.com/feeds/posts/summary?max-results=1000&alt=json-in-script&callback=loadtoc">
</script>
<script type="text/javascript">
var accToc=true;
</script>
<script src="http://abu-farhan.com/script/acctoc/accordion-pack.js" type="text/javascript">
</script>
put on your blog with widgets menmbahkan script / text javascript
whatever you want in the store at the Manah in your log.
after complete store and see the results.
http://www.pcmag.com/article2/0,4149,1306756,00.asp
excl.gif No Active Links, Read the Rules - Edit by Ninja excl.gif
Google is clearly the best general-purpose search engine on the Web (see
www.pcmag.com/searchengines
But most people don't use it to its best advantage. Do you just plug in a keyword or two and hope for the best? That may be the quickest way to search, but with more than 3 billion pages in Google's index, it's still a struggle to pare results to a manageable number.
But Google is an remarkably powerful tool that can ease and enhance your Internet exploration. Google's search options go beyond simple keywords, the Web, and even its own programmers. Let's look at some of Google's lesser-known options.
Syntax Search Tricks
Using a special syntax is a way to tell Google that you want to restrict your searches to certain elements or characteristics of Web pages. Google has a fairly complete list of its syntax elements at
www.google.com/help/operators.html
. Here are some advanced operators that can help narrow down your search results.
Intitle: at the beginning of a query word or phrase (intitle:"Three Blind Mice") restricts your search results to just the titles of Web pages.
Intext: does the opposite of intitle:, searching only the body text, ignoring titles, links, and so forth. Intext: is perfect when what you're searching for might commonly appear in URLs. If you're looking for the term HTML, for example, and you don't want to get results such as
www.mysite.com/index.html
, you can enter intext:html.
Link: lets you see which pages are linking to your Web page or to another page you're interested in. For example, try typing in
link:http://www.pcmag.com
Try using site: (which restricts results to top-level domains) with intitle: to find certain types of pages. For example, get scholarly pages about Mark Twain by searching for intitle:"Mark Twain"site:edu. Experiment with mixing various elements; you'll develop several strategies for finding the stuff you want more effectively. The site: command is very helpful as an alternative to the mediocre search engines built into many sites.
Swiss Army Google
Google has a number of services that can help you accomplish tasks you may never have thought to use Google for. For example, the new calculator feature
(www.google.com/help/features.html#calculator)
lets you do both math and a variety of conversions from the search box. For extra fun, try the query "Answer to life the universe and everything."
Let Google help you figure out whether you've got the right spelling—and the right word—for your search. Enter a misspelled word or phrase into the query box (try "thre blund mise") and Google may suggest a proper spelling. This doesn't always succeed; it works best when the word you're searching for can be found in a dictionary. Once you search for a properly spelled word, look at the results page, which repeats your query. (If you're searching for "three blind mice," underneath the search window will appear a statement such as Searched the web for "three blind mice.") You'll discover that you can click on each word in your search phrase and get a definition from a dictionary.
Suppose you want to contact someone and don't have his phone number handy. Google can help you with that, too. Just enter a name, city, and state. (The city is optional, but you must enter a state.) If a phone number matches the listing, you'll see it at the top of the search results along with a map link to the address. If you'd rather restrict your results, use rphonebook: for residential listings or bphonebook: for business listings. If you'd rather use a search form for business phone listings, try Yellow Search
(www.buzztoolbox.com/google/yellowsearch.shtml).
Extended Googling
Google offers several services that give you a head start in focusing your search. Google Groups
(http://groups.google.com)
indexes literally millions of messages from decades of discussion on Usenet. Google even helps you with your shopping via two tools: Froogle
CODE
(http://froogle.google.com),
which indexes products from online stores, and Google Catalogs
CODE
(http://catalogs.google.com),
which features products from more 6,000 paper catalogs in a searchable index. And this only scratches the surface. You can get a complete list of Google's tools and services at
www.google.com/options/index.html
You're probably used to using Google in your browser. But have you ever thought of using Google outside your browser?
Google Alert
(www.googlealert.com)
monitors your search terms and e-mails you information about new additions to Google's Web index. (Google Alert is not affiliated with Google; it uses Google's Web services API to perform its searches.) If you're more interested in news stories than general Web content, check out the beta version of Google News Alerts
(www.google.com/newsalerts).
This service (which is affiliated with Google) will monitor up to 50 news queries per e-mail address and send you information about news stories that match your query. (Hint: Use the intitle: and source: syntax elements with Google News to limit the number of alerts you get.)
Google on the telephone? Yup. This service is brought to you by the folks at Google Labs
(http://labs.google.com),
a place for experimental Google ideas and features (which may come and go, so what's there at this writing might not be there when you decide to check it out). With Google Voice Search
(http://labs1.google.com/gvs.html),
you dial the Voice Search phone number, speak your keywords, and then click on the indicated link. Every time you say a new search term, the results page will refresh with your new query (you must have JavaScript enabled for this to work). Remember, this service is still in an experimental phase, so don't expect 100 percent success.
In 2002, Google released the Google API (application programming interface), a way for programmers to access Google's search engine results without violating the Google Terms of Service. A lot of people have created useful (and occasionally not-so-useful but interesting) applications not available from Google itself, such as Google Alert. For many applications, you'll need an API key, which is available free from
CODE
www.google.com/apis
. See the figures for two more examples, and visit
www.pcmag.com/solutions
for more.
Thanks to its many different search properties, Google goes far beyond a regular search engine. Give the tricks in this article a try. You'll be amazed at how many different ways Google can improve your Internet searching.
Online Extra: More Google Tips
Here are a few more clever ways to tweak your Google searches.
Search Within a Timeframe
Daterange: (start date–end date). You can restrict your searches to pages that were indexed within a certain time period. Daterange: searches by when Google indexed a page, not when the page itself was created. This operator can help you ensure that results will have fresh content (by using recent dates), or you can use it to avoid a topic's current-news blizzard and concentrate only on older results. Daterange: is actually more useful if you go elsewhere to take advantage of it, because daterange: requires Julian dates, not standard Gregorian dates. You can find converters on the Web (such as
CODE
http://aa.usno.navy.mil/data/docs/JulianDate.html
excl.gif No Active Links, Read the Rules - Edit by Ninja excl.gif
), but an easier way is to do a Google daterange: search by filling in a form at
www.researchbuzz.com/toolbox/goofresh.shtml or www.faganfinder.com/engines/google.shtml
. If one special syntax element is good, two must be better, right? Sometimes. Though some operators can't be mixed (you can't use the link: operator with anything else) many can be, quickly narrowing your results to a less overwhelming number.
More Google API Applications
Staggernation.com offers three tools based on the Google API. The Google API Web Search by Host (GAWSH) lists the Web hosts of the results for a given query
(www.staggernation.com/gawsh/).
When you click on the triangle next to each host, you get a list of results for that host. The Google API Relation Browsing Outliner (GARBO) is a little more complicated: You enter a URL and choose whether you want pages that related to the URL or linked to the URL
(www.staggernation.com/garbo/).
Click on the triangle next to an URL to get a list of pages linked or related to that particular URL. CapeMail is an e-mail search application that allows you to send an e-mail to google@capeclear.com with the text of your query in the subject line and get the first ten results for that query back. Maybe it's not something you'd do every day, but if your cell phone does e-mail and doesn't do Web browsing, this is a very handy address to know.
Source:
CODE
http://www.extrememhz.com/dlcomp-p1.shtml
Since the introduction of double layer DVD writers, the interest has been quite overwhelming and is why we keep bringing you reviews of these highly popular drives. The anticipation has now turned into down right obsession and it has become a key component in any current or new system build, thanks to the declining prices and continued media hype. Manufacturers are quite aware of the fascination and is why they have each been releasing their own products which excel in at least one area of the testing methodology used in most reviews. This has led to some confusion as to which drive is best suited for the individuals needs. Today, we compare four 16x double layer drives and highlight both the strong and weak points in order to give you a better idea of which drive is best suited for you.
In this comparison guide, we will be looking at four of the top 16x drives to hit the market, the Pioneer DVR-108, NEC ND3500A, Lite-On SOHW-1633s and the new LG GSA-4160B. We will cover everything from design and features to performance and price. Let's begin with a quick look at each of these drives.
As far as the front bezel design goes, the LG-GSA4160B is by far the most attractive drive of the bunch. However, for those who are looking for a headphone jack, the Lite-On drive is the only DL writer offering a headphone jack, as well as volume control. The Pioneer and NEC drives, in my opinion, are the ugliest drives, with a very plain look that just wants to make you hide the drive period. Although we only obtained the 4160B in black, all these drives are offered with both white and black bezels. If you opt for the more expensive Pioneer "XL" model, it has the most impressive looks of any drive in the market. However, this will come at a very hefty price tag, considering they contain different firmware as well that offer a few extra features.
So, we have determined which is the sexiest-looking drive, but what about performance? I've done some extensive testing on each model to determine which is indeed the most impressive of the bunch. But before we show you performance results, let's briefly look at the features and what they have to offer.
Features
Each one of these drives has there disappointments when it comes to features. Let's compare each to see what they really offer.
DVD Writing
DVD+R DVD-R DVD+RW DVD-RW
LG GSA-4160B 16x 8x 4x 4x
Lite-On SOHW-1633s 16x 8x 4x 4x
NEC ND-3500A 16x 16x 4x 4x
Pioneer DVR-108 16x 16x 4x 4x
While all these drives are indeed 16x models, only two will write to both formats at this speed. The LG GSA-4160B and the Lite-On SOHW-1633s only support 8x DVD-R writing. So if you are one who only prefers this format, the NEC or Pioneer would be the best choice. All of these drives support writing to DVD re-writable media at 4x.
DVD+R9 Double Layer Writing
Write Speed
LG GSA-4160B 2.4x
Lite-On SOHW-1633s 2.4x
NEC ND-3500A 4x
Pioneer DVR-108 4x
The major disappointment with both the LG and the Lite-On 16x drives is the lack of 4x double layer writing support. Pioneer and NEC seem to be the only manufacturers to jump in and release second generation double layer drives supporting much faster 4x writing. In fact, the jump from 2.4x to 4x is quite substantial as we will show you a bit later in this comparison.
DVD-RAM Support
Supported Read Write
LG GSA-4160B YES 5x 5x
Lite-On SOHW-1633s NO NO NO
NEC ND-3500A NO NO NO
Pioneer DVR-108 YES 2x NO
Now this is where both the LG GSA-4120B and GSA-4160B shine above the rest. In fact, it is what has made these drives the most popular DVD writers on the market. Unlike the rest in the roundup, it is a triple format burner, offering full support for DVD-RAM media. The other drives do not support it, with the exception of the Pioneer DVR-108 which supports reading of DVD-RAM discs at 2x. I personally don't see the point in offering only read capabilities, but it's at least one extra feature added to distinguish it from the rest. Fast 5x support of the LG GSA-4160 will actually be tested a bit later in this article.
CDR Writing
CDR CDRW
LG GSA-4160B 40x 24x
Lite-On SOHW-1633s 48x 24x
NEC ND-3500A 48x 24x
Pioneer DVR-108 32x 24x
The fastest CDR writers of the bunch are the Lite-On SOHW-1633s and the NEC ND-3500A. With their support for 48x writing, they make a great all-in-one drive for many users. The only drive lacking in this lineup is the Pioneer DVR-108. Why they opted for only 32x writing is still quite puzzling and is actually why I have found that many are choosing the NEC over the Pioneer. The LG GSA-4160B should not be left out of consideration though. We will show you later that the difference in write times between 40x and 48x is not much to brag about.
Bitsetting Support
One feature I've found that is most important for many users is bitsetting support. Let's compare these drives and see what they offer.
DVD+R/RW Support DVD+R DL Support
LG GSA-4160B NO NO
Lite-On SOHW-1633s YES NO
NEC ND-3500A NO YES
Pioneer DVR-108 NO YES
The LG GSA-4160B does not offer bitsetting support out of the box. However, it is very likely that you will be able to obtain support through an excellent third-party tool called DVDInfo Pro. Right now, they only support the GSA-4120B, but I'm confident with the author that support for this drive will be likely. LG firmware is very hard to hack, however some select few have been able to do so. Using Lite-On's booktype utility, you can change the booktype of DVD+R/RW media, however, the firmware does not automatically change booktype of DVD+R DL discs to DVD-ROM like the NEC and Pioneer models do.
Additional Features
As far as other features go, all these drives have a 2MB buffer but offer some sort of buffer under-run protection, which all work exceptionally well. This is especially useful if you will be burning discs at 16x, which I personally don't recommend just yet. As our individual tests of these drives revealed, burning at this speed is quite unstable, with the exception of the Lite-On SOHW-1633s.
