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Examining ICMP Flaws
An anonymous reader writes "A recent internet-draft pointed out a number of security flaws in the design of the ICMP protocol. Most open source projects and vendors have addressed the flaws to some level, but this interesting article on KernelTrap examines the true extent of the problem, and how so far only OpenBSD has implemented all possible counter-measures. Theo de Raadt is quoted saying, "here we have a 20 year old protocol, a part of the Internet infrastructure that hasn't been touched in 10 years and we were all sure was right, and now is cast in doubt.""
In that case... I See More Patches. :-(
Beware: In C++, your friends can see your privates!
The spec calls for a sequence number in the block. Vendors aren't checking it. There are a lot of technical details about how TCP connections can be slowed down by a ICMP attack, but if the vendors checked the sequence number it would make it almost impossible to implement these attacks.
Researcher found the bugs, tried to work with major vendors. Lawyers got involved, turns out Cisco had been working on a fix for years (so they say). Seems like vendors are more concerned about getting credit than fixing the bugs.
Reading between the lines, I take it the major vendors have patched their stacks and life is good. Linux implemented all the fixes for all the errors, but addressing the sequence number should be enough for now.
Makes me wonder: what did the guys writing the code back in the 80s think about the sequence number, anyway? It was obviously there for some reason. I guess because it wasn't part of the "official" spec it was ignored? Shame, that. That was back in the day when people probably didn't think of ICMP being used as a cyber attack vector.
Smart Identification Of Cost Savings, One Key to Program Management
While the patent issue was happening with Cisco, CERT/CC created a mailing list to allow vendors to communicate amongst themselves about the newly discovered vulnerability. "They blamed me for submitting my work," Fernando said in exasperation. "One of Cisco's managers of PSIRT said I was cooperating with terrorists, because a terrorist could have gotten the information in the paper I wrote!"
Of course. We know of problems but we are going to go the Security by Obscurity route and then when the cover is blown we'll claim they are supporting terrorism instead of admitting that we were wrong!
If the terrorism route doesn't work we always have the patent on the issue to sue him with!
Way to fucking go, thanks Cisco!
"We don't put HTTP servers in the kernel." Umm, khttpd is pretty much an http server in the kernel. But more on topic, what a pain in the ass it would be to have to install and maintain yet another network server. I'd rather just have it in the kernel personally. If I really had a problem with it, I'd take it out. That's the beauty of Linux.
ICMP is in the kernel because it's part of TCP/IP, which wouldn't be hard to remove from a Linux kernel.
Kinda makes all your other services pointless thought, don't it.
http://en.wikipedia.org/wiki/TCP/IP
This should not have been modded up. ICMP is not a service like http or smb, though if your only experience with icmp is ping, it might seem that way. ICMP is a low-level part of the network stack, used internally by TCP/IP, and as such it needs to reside wherever the network stack resides. The entire network stack could be moved to userland, but that is a separate question.
We don't put HTTP servers in the kernel.
I'm sure this will end up redundant but I'm going to comment anyway.
I give you TUX
The whole reason for monolithic kernels like Linux is performance and simplicity. Having to do a context switch for every single packet gets expensive...
Linux IT Consulting and Domino Development in Michigan
RFC 792 dates back sep 1981.
wikipedia
You have been modded up, but this is a pretty uninformed argument. ICMP is part of TCP/IP, which you definitely want in the kernel. I guess it would be possible to put it user space, but performance would be terrible. In any case, user space wouldn't protect against what the article is talking about.
As a matter of fact, people DO put HTTP servers in the kernel. There is more than one Linux in-kernel HTTP server around, and parts of IIS run in kernel on later versions of Windows. If you really, really care about performance (hint: Apache doesn't, its strength is flexibility) then the cost of kernel calls and copying data from user space to kernel space is important.
sheep.horse - does not contain information on sheep or horses.
Please google TCP/IP, then quiz yourself against your grandmother. If she knows more than you about how networks operate, read more. Once you manage to outwit her you are free to state your apologies here.
The scary thing is that the parent is talking about ICMP without actually knowing what it is.
You see, this is one of the failures of the moderation system: when someone posts something like this, it seems intelligent because it mentions a lot of familiar things, but overally it's not even making sense. The problem is that moderators work like this:
Argument: check
Clear line of thinking: check
Windows comparison: check
The problem is that this checklist does not include VERIFYING THINGS like what ICMP is. This is how the parent got +5, insightful while it's one of the most misinformed posts i've seen in a while.
It takes a man to suffer ignorance and smile
Be yourself no matter what they say
How the heck did this get modded insightful?
ICMP runs on a different layer than all of the services you mentioned. ICMP is a network layer protocol (like IP and IPv6, also called "layer 3"), and all the protocols you mentioned are application layer (layer 7) protocols. There's no direct comparison to be made to any of the protocols (HTTP, SMB, FTP and NFS) you mentioned.
If you want to compare having ICMP in the kernel to other sinilar protocols, your best argument (if you can call it that) is that we should have *IP*, another layer 3 protocol, "running as an ordinary user process, not root, and especially not as a kernel process." Obviously, IP *is* included in the kernel, for plenty of good reasons. Comparing ICMP to application-layer protocols like HTTP holds no weight whatsoever, unless you're completely ignorant of network fundamentals.
How it got modded to +5 Insightful baffles me. I'd have thought this crowd would have a better handle on the basics.
Putting things in the kernel rather than user space isn't purely a performance decision, which seems to be the logic behind your comment. If that was the case, there'd be a whole lot of things that should be moved to user space, such as the dumb terminal or low speed serial port handling.
A lot of things should be put in user space if they can. When those things are put in the kernel, it is usually because the kernel is a better location than userspace. Sometimes it is for performance, sometimes for other reasons. It is a trade off of course.
UDP relies on ICMP to generate unreachable port messages. Coming up with a setup where the in kernel UDP code calls a userspace ICMP process to generate those messages is more complicated than having ICMP as part of the kernel.
The Internet's nature is peer to peer - 20050301_cs_profs.pdf
Yes... it could be done outside of the kernel. The problem is that it's basically a required component of IP (the two interact closely). IP uses ICMP to report errors, for instance. If ICMP were in a user process, it would have to jump the kernel/user boundary every time, which could become very expensive.
ICMP really isn't a server. It's a protocol for performing odd tasks that don't quite belong inside IP itself but that are more or less essential for it to function. 'ping' is just one of about 16 message types ICMP supports. The others involve routing, destination unreachable messages, source quench ("slow down!"), etc.
I think a better design would be to have the entire networking subsystem in userland.
Incidentally, my current project is writing a tun/tap-based IP stack entirely in C#. It's mostly for fun, but when it's finished it'll be a complete userland networking subsystem. (Current status: decodes and defragments IP packets, starting to implement ICMP.)
-John
I think you could send a redirect via ICMP too, to generate your own man-in-the-middle attack. It's been too long since I've read the RFC.
DHCP has a whole bunch of issues too. For example, what if a DHCP client gets a DHCPACK from some machine? I'll bet that it would just reconfigure itself using the information in the packet. Bam, you've got a man-in-the-middle attack.
Nice job RTA dorkface:
"The ICMP flaw is in the design of the protocol, not in any specific implementation."
You listed flaws in implementations, none dealing with a flaw inherent to the ICMP protocol.
"What kind of music do pirates listen to?" -Paul Maud'dib
"Yeeeaaarrrrr n' Bee!!" -Stilgar, Leader of Sietch Tabr
We knew about the problems with ICMP when we first designed applications around it in the mid 80s. But at that time it just was not critical or exposed enough for us to really spend too much time planning workarounds or suggesting changes to the specification.
At that time we really didnt think that there would be such a huge number of users for what we thought was something with a very limited audience.
Often when Internet providers disable your cable/DSL/LAN connection for security or billing reasons, they just block TCP and UDP but leave ICMP available. I've observed Georgia Tech's ResNet to do this, and reportedly Adelphia's cable ISP does the same. You can ping to your heart's content, but can't send data.
Except that you can.
A ping packet (ICMP echo request) can have a completely arbitrary payload. You can put any data you want there. You could even tunnel IP inside it. You would have to have to have a friendly server on the outside to receive these packets and forward the contents, but that's easily done.
This trick might also be useful for tunnelling past content filters. I don't think any of them scan ICMP packets.
I'm writing a simple userspace IP stack (gets packets from the tun/tap interface), and I intend to try this out once it's a bit more mature.
-John
Null route any ASs that still allow spoofed egress. (Welcome to 1998)
My network sure as hell doesn't allow any packets to leave that claim to be from an IP that isn't on our network. Does yours? It shouldn't.
I'm pretty sure our upstreams will blackhole any packets emitted on our fiber that don't belong to our ranges too. Yours should as well (if you are an exception to this rule, you'll know).
After that, it is only a matter of watching the managed switches. They'll alert us to MAC collissions faster than you can say "shallow grave".
See that "Preview" button?
This seems very typical of science in all fields. An unproven theory goes unrebutted for some time untill someone realizes we made a big mistake. The world was once flat remember guys! One thing this should point us to is that no matter how solid something appears, it will always be broken whether it be a theory, a protocol or yes even the fortress known as open bsd *duck* Jokes a side, remember nothing is secure.
Later,
Phil
IRC networks have been plagued with ICMP unreachables for years
u ke.html
http://www.rs-labs.com/papers/tacticas/ircutils/p
nothing new to see here, move along.
Using spoofed unreach packets to drop TCP sessions has been around for a LONG time - it used to be called a "nuke" (before the Windows OOB attack, "WinNuke", became more widely known). I know that I've heard of the quench spoof attack, but hadn't heard of the path MTU attack, yet. Using ICMP redirect messages to arrange MITM attacks was also an old one, but I don't think that most stacks pay attention to redirect any more.
i p/browse_thread/thread/439b09e36f4738eb/2eacbab1d4 9e966d?q=icmp+unreach+nuke&rnum=3&hl=en#2eacbab1d4 9e966d e curity/browse_thread/thread/37d9a0a870080133/711f4 cc20af1a450?q=icmp+quench+spoof&rnum=1&hl=en#711f4 cc20af1a450 _ thread/thread/e96bd4e594c808d5/3f66eac2a5aa8665?q= icmp+path+mtu+spoof&rnum=2&hl=en#3f66eac2a5aa8665
Here's a post from 1993, for example:
http://groups.google.ca/group/comp.protocols.tcp-
One from 2000:
http://groups.google.ca/group/sol.lists.freebsd.s
One from 2003:
http://groups.google.ca/group/linux.kernel/browse
While these kinds of risks have been known for a long time, there hasn't really been much attempt to mitigate them. Fernando seems to be a little green, initially thinking that he discovered new vulnerabilities, but he's doing the right thing in pressuring for methods of mitigation. It's a hard fight against complacency. Some of the ideas are clever, but it'll take a lot of convincing to change something so low level as ICMP. For how simple ICMP is, it has lots of security issues; it has got to be made more complicated very carefully.
ping is actually an abbreviation, it stands for packet inter-network groper.
Fernando was interested in discussing the ideas with his peers, but was concerned about vendors trying to patent his suggested fixes.
Aren't patents lovely for innovation and growth of technology?
Not to be a flame/ass/flaming-ass or whatever...
Actually, first the world was dish shaped, then it was cilindrical, but the God Atlas has been carrying a globe on his shoulder for about 2500 years already. The American view of the world as a flat Pizza, is very modern...
Oh well, what the hell...
As someone who once implemented ICMP (in 1982, before BSD, even), I should say something.
First, ICMP is a layer 3 protocol, like TCP and UDP. ICMP is IP protocol #1; TCP is #6 and UDP is #17.
Second, it's quite feasible to put ICMP in user space. I'm writing this on a QNX system where it's in user space. My 1982 implementation was also in user space, as part of 3COM's UNET. Linux doesn't do it that way, but it's not fundamental that ICMP must be in the kernel. It needs to have a mechanism to pass messages to the other protocols, but that's a local message passing problem. But I'm not going to rehash the ever-growing monolithic kernel issue here.
Third, we knew about many of those vulnerabilities back in the 1980s, but weren't as concerned about them because the Internet was a DoD/NSF operation. Destination Unreachable and Source Quench messages used to be taken more seriously than they are now. Destination Unreachable told you where the network was down, and Source Quench told you where it was congested, basic network management info back then. Today, nobody does network management that way and many TCP stacks don't do much, if anything, with ICMP information. I used to encourage the use of Source Quench for congestion management (see my RFC on this, from 1984), but it's far less appropriate today. Back then, we were concerned about packet loss through transmission errors, a frequent occurence with leased-line synchronous modems. So, when a packet was lost, the question was whether you should retransmit rapidly (appropriate for an error) or slowly (appropriate for congestion). Source Quench could disambiguate that situation. Today, it's assumed that packets are lost almost entirely through congestion, since the lower levels are of much better quality than they used to be.
I run OpenBSD stable, and some belligerent asshole stays up all night worrying about the best possible response to the latest threats. Sure, I will buy a CD http://openbsd.org/items.html#37.
And Theo, thank you for being a belligerent asshole for the good guys.
do you post just for the hell of posting? Brilliant.
13 million whoo!
Congratulations on having the 13,000,000 millionth post :)
Congatulations on post 13 million.5 077&cid=13000000
http://developers.slashdot.org/comments.pl?sid=15
https://www.gnu.org/philosophy/free-sw.html
There should be absolutely no discussion of ICMP without considering the fundamental research carried out by Orfin Arkin. His work should be read by anyone willing to discuss the issue beyond the /. gossiping ...
P.S. ... what the heck is going on with the HTML formatted postings?!?
== With enough Will Power, one could move mountains. With enough Brains, one would just leave them where they are ==
What you wrote is right on except for the minor quibble that ICMP/TCP/UDP are not all layer 3 protocols.
According to the OSI Model:
Layer 1: Physical
Layer 2: Data Link
Layer 3: Network (IP goes here)
Layer 4: Transmission (TCP goes here)
Layer 5: Session
Layer 6: Presentation
Layer 7: Application
UDP and ICMP are kind of harder to classify, although I've most often seen UDP placed in Layer 4 and ICMP in Layer 3. If you were referring to the TCP/IP network model which better represents TCP/IP (go figure), they still wouldn't be at the same layers.
Layer 4: Application (HTTP)
Layer 3: Transport (TCP, UDP)
Layer 2: Internetwork (IP, ICMP)
Layer 1: Network Access (eg Ethernet)
And how nicely ironic the 13,000,000nth post is..
Is there anything better than clicking through Microsoft ads on Slashdot?
Thing is, none of those "vulnerabilities" matter.
Yes, they're real. Yes, you really can use them to bring non-OpenBSD servers to a halt -- for as long as you keep sending packets.
But think it through: to use those vulnerabilities without getting very busted very fast, you have to have control of a botnet -- a significant anonymous source of packets. If you have control of a botnet, you can DDOS the server to death regardless of whether it has these vulnerabilies -- simply fill the pipe with normal packets.
And guess what? Getting a hold of a botnet is a lot easier than exploiting these vulnerabilities.
So, on a practical level, whats the difference between fixing these particular denial-of-service vulnerabilities and ignoring them? Damned if you do, damned if you don't. Better to spend your time worrying about problems whose solution might actually make a difference.
Moderating "-1, Disagree" is simple censorship. Have the guts to post your opinion.
Then why is it that the OpenBSD implementation of the very same ICMP protocol is claimed to be flawless?
Chuuch. Preach. Tabernacle.
I'm thinking, they are attacking me, so I'll attack them back! (Normally, I drop all garbage packets).
You are being MICROattacked, from various angles, in a SOFT manner.
This is the biggest problem with large companies. Sure, it is has been pointed out adnausium over the years in various sources -The Mythical Man Month and The Innovators Dilemma being two very good ones. It is too bad that our network is now being ruled by bandits because of it. MS has become everything that it hated about IBM. Cisco has so much hardware out there that IOS has to be tested on everything before a new release. How can it be possible that when FOSS gets updated and corrected quicker? Of course, I work for a large company, and I see how long it takes to get a simple task completed. I'm guessing it has a lot to do with modivation. The open source folks really do believe in their product. For the people working in big companies, it is just a paycheck.
Of course, there's always this possibility
"Well, good luck finding a judge that doesn't run a bestiality site."
13,000,000 millionth post
We can do better than this.
Congratulations on having the 13 millionth post!
Probably just a typo, but I wanted to clarify a mistype in your post.
ICMP IS a subset of the Internet Protocol(IP). IP, part of TCP/IP, has an error reporting mechanism for when things get screwed up, it is called ICMP. It doesn't sit on top nor beside IP, it sits inside of it, logically speaking.
Both ICMP, which is consider its own entity at times, but is a subset of IP as a whole, and IP are at layer 3. The Networking layer.
TCP and UDP are layer 4.
microkernels(as mentioned in another post) do exactly this: move as much OUT of the kernel as possible, including the networking (TCP/IP) stack. This isn't a bad idea, necesarily, it gives some advantages that microkernels are all about. If your networking stack gets completely destroyed, it doesn't take down your kernel, etc, etc.
monolithic kernels, like Linux(and most OSes, since they are 'easier' and more commonly accepted design) put more things inside the kernel like the networking stack. Not everything, but more things than a microkernel.
All that being said, even in linux, you could still write an userspace TCP/IP stack and use it, AFAIK. Though things like performance would be an issue.
FYI, I'm a Time Warner employee in Austin, TX.
When we disable a modem for non-payment or virus/spam abuse, we do it through rebooting the modem with a new BIN file. Once done, you will not get an IP address. The modem will still have a 10.net address attached to our network to configure. However, it's not accessible so don't bother wasting your time.
Regardless if you could get online through a disabled modem, don't do it. Theft of cable service (including internet service through our cable) is federal crime. So don't even THINK about getting crafty with your connection that has been explicitly disabled for non-payment.
Life is not for the lazy.
it is not illegal to write the code. It would be useful to see if this hack does work. If so, then it will point out weaknesses in the networks as well as an issue with the protocol.
Now, with that said, Yeah, it is theft, and it is federal. So, I am sure that s?he will not be using illegally. Or at least, I hope not.
I prefer the "u" in honour as it seems to be missing these days.
becuase you don't need to physically go to a computer to break into it
There are places where the networks are not touching,and there are places where they are-Boeing's Lori Gunter
The power grid is massively overloaded - especially in the Northeast and California, but Oregon has been blacked-out by single line failures before. As for the Internet, an attack on ICMP might be of academic interest, but it seems to me that they'd simply sever critical fibre. Less stoppable and would take substantially longer to repair.
And if you really DID want to launch a data-driven attack, poisoning the router tables or DNS tables would have a larger impact, last longer and would be much harder to trace than an ICMP flood.
In other words, you are absolutely right that the Cisco manager was playing an emotive card, rather than saying anything of any technological credibility. It is not only an utterly unlikely choice of weapon for such folk (too many alternatives that would have greater impact and would be more likely to work), but there is nothing in this new study that hasn't been known for a long time.
If Cisco has a solution already, but competitors (by and large) don't, then Cisco obviously would have an edge in the market, if there was a panic rush to secure systems. On the other hand, they'd lose that edge if competitors upgraded their software prior to such a rush.
The somewhat unpleasent implication would seem to be that individuals within Cisco were considering launching an ICMP-based attack of their own, to get people to switch to Cisco products. (I doubt Cisco itself would touch such a plan with a 10' barge pole.) Right about now, I'd want to know what kind of stock this manager has in Cisco, what kind of performance bonuses he gets and whether he knows DDoS-er Skript Kiddies. If there are provable means and motive, then I think we know why he was so upset at this becoming public.
Suspicion, regardless of why or what, is just that and nothing more. However, were it to transpire that the manager could have personally profitted from an ICMP-based attack, then I think some serious questions need to get asked very quickly.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
When I worked at CheckPoint, back in 2002, I was project manager for SmartDefence. We integrated protection against the PMTU window size problem into SmartDefence, and we had protection against it ever since version 1 (that is - late 2002). You can set the minimal value a PMTU window can shrink to, with ~300 being the default minimum.
The reason we didn't take credit for discovering this at the time was that I picked it up myself from a side note in one of the security mailing lists. I couldn't find at the time the place this was first published, and I sure as hell won't be able to locate it now, but this is not a newly discovered problem, nor is it non-public. The attention is new, but the problem was known even before.
As I no longer work for CheckPoint, I don't know whether they'll make a media circus from this or not. I don't really care either.
Shachar
As a state gets corrupt, its laws multiply; the most corrupt states have the most numerous laws. (Tacitus, Annales 3:27)
The whole idea behind the RFC system was that the documents, once published, are unchanging. Just like every standard ANSI and ISO publish. There can be and often are documents that revise the protocol, but that's the nature of the standards game and even the ISO does it. Despite common references to ISO standards by number, their proper names are ISO nnnnn:yyyy. For example, SGML is ISO 8879:1986, not ISO 8879, and it has been updated three times since it was issued, by ISO 8879:1986/Cor 1:1996, ISO 8879:1986/Cor 2:1999 and ISO 8879:1986/Amd 1:1988.
And "back in the day", if you didn't implement part of an RFC for a protocol you implemented, you got lambasted for it. Search around the net for the early 1908s discussions of the TCP Bakeoffs if you want to see how serious we were about it.
Again: you have to guess the source port, too. There are very few tcp protocols with predictable source ports nowadays. So it's not 2^32/windowsize but probably (2^16-1024)*2^32/windowsize. Have fun brute forcing that.
Not only that, but unless you *are* MITM, you'll never actually know that you've succeeded. So not only do you have to bruteforce it (which will take a ton of bandwidth) you can't know when to stop - which means that you have to run the entire gamut in order to be sure you're successful.
And if the connection restarts (I believe the timeouts listed were 10 minutes), you've gained absolutely nothing.
If you have the bandwidth to brute force this, you might as well be doing a DDoS.
This issue has to be considered, but as D. Adams said: Don't panic!
Very succintly put.
First, while source quench is pretty blind, it isn't much of an issue - it's ignored for TCP and I'm not sure that it's used for UDP either (if it is, few important services use UDP over the internet).
Path MTU spoofing is really just a variation of the ICMP Unreach spoof attack (same ICMP type). Unreach packets need to "quote" the header of the packet that couldn't be delivered - including source (random 1024-65535) and target port numbers - this allows the sending host to know what connection is being affected. In order for the attacked host to accept a spoofed unreach, the unreach needs to quote the right source IP/port and target IP/port. Most of the time, the source IP, and target IP/port are known but the source port could be one in a few thousand. It used to be that, on modem connections, sending thousands of unreach packets took a few minutes, but now it can be done in seconds or less. Now you can even guess the source IP (drop all connections from a network to a server). Thus, now, the attack is essentially (if not technically) blind since you don't have to find the right combo - you just send all combos.