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Linux Bug Leaves USA Today, Other Top Sites Vulnerable To Serious Hijacking Attacks (arstechnica.com)
Dan Goodin, reporting for Ars Technica: Computer scientists have discovered a serious Internet vulnerability that allows attackers to terminate connections between virtually any two parties and, if the connections aren't encrypted, inject malicious code or content into the parties' communications. The vulnerability resides in the design and implementation of RFC 5961, a relatively new Internet standard that's intended to prevent certain classes of hacking attacks. In fact, the protocol is designed in a way that it can easily open Internet users to so-called blind off-path attacks, in which hackers anywhere on the Internet can detect when any two parties are communicating over an active transmission control protocol connection. Attackers can go on to exploit the flaw to shut down the connection, inject malicious code or content into unencrypted data streams, and possibly degrade privacy guarantees provided by the Tor anonymity network. At the 25th Usenix Security Symposium on Wednesday, researchers with the University of California at Riverside and the US Army Research Laboratory will demonstrate a proof-of-concept exploit that allows them to inject content into an otherwise legitimate USA Today page that asks viewers to enter their e-mail and passwords.
And using SSL/TLS or ipsec would basically close this hole entirely. What we see here is that it might be a little easier to inject into non-ciphered non-authenticated content and there may be a slightly larger scope of attackers positioned to do it.
NON STORY
There has always been a risk that plan text traffic could be tampered with, nothing has really changed here and I don't see that risk even being significantly increased.
Repeal the 17th Amendment TODAY! Also Please Read http://www.gnu.org/philosophy/right-to-read.html
Do you have some examples of secure closed source? It's hard to find examples that have an install base in the server world as big as Windows or Linux, and examples of less used systems can be a bit suspect as they could simply be a statistical anomaly or not well known and not a popular target in the hacker scene. (although some of those guys will dig into pretty much anything, especially if they can work out a cool presentation at DEF CON)
Linux vulns tend to get corrected pretty quickly, as there are a lot of contributors. And like most vulns the easy way to avoid this is not to add so many damn features.
PS - OpenBSD doesn't have this flaw, and it is also open source.
“Common sense is not so common.” — Voltaire
Most ordinary users don't look at the source because they just want a computer that works and does what they want it to. However, publishing source code allows hackers to find the vulnerabilities more easily than guessing them with closed source software. Open source software is inherently insecure and closed source offers far greater security.
At the 25th Usenix Security Symposium on Wednesday, researchers with the University of California at Riverside and the US Army Research Laboratory will demonstrate a proof-of-concept exploit that allows them to inject content into an otherwise legitimate USA Today page that asks viewers to enter their e-mail and passwords.
It looks to me that by having the source code available, these researchers - white hats - found the vulnerability before the bad guys did. Of course, USA Today being highjacked wouldn't exactly be this horrible ordeal or any real loss to humanity.
I wrote a tiny bit of IPsec code about 15+ years ago, for a router company thinking it would take off. It still hasn't taken off, and I've given up on anyone giving two shits about rolling out IPsec in any significant way.
“Common sense is not so common.” — Voltaire
The DOS possibilities are ignored by you. This is a significant problem. Why bother with a DDOS via a botnet when you can do this kind of thing from a single host?
HBI's Law: Frequency of calling others Nazis is directly correlated with the likelihood of the accuser being Communist.
The above does not seem believable — in principle. Unless by "hackers anywhere" means "hackers able to login anywhere".
Would any resident network experts care to comment?
Why is my real account disabled?
I'm not in the habit of responding to obvious trolls, but this case makes very clear the flaw in the logic of people who actually believe that open source is insecure.
The bug is in the specification, which is necessarily open in order to create inter-operable systems. And what is code, if not a machine readable specification?
The idea that closed source is more secure, taken to its logical end, is an argument for closed systems that don't inter-operate with other systems. Their operation would have to be entirely secret and proprietary.
The bug is in the RFC, which Linux implements faithfully. I find it funny that the only reason Linux is the only mainstream operating system that is vulnerable is because it's the only mainstream operating system that implements the RFC. And yes, it is a very critical bug, one which the RFC needs to address, too.
Also, the fix was committed a few weeks ago, but distributions haven't pushed it out yet (at the time the arstechnica article was written).
I read the brief article, and read RFC5961, and here's a quick summary:
A TCP connection is uniquely identified by the combination of: Source IP address; Destination IP address; Source port number; Destination port number. TCP also has a sequence number, which helps reorder packets. It also helps prevent spoofing, but spoofing is still possible. Any computer on the internet can craft a packet to send to a Destination IP address and Destination port with all the other fields spoofed. A spoofer cannot receive a reply (the Destination machine will send any replies to the indicated Source IP address, which the spoofer cannot see).
So, it's possible to inject SYN and RST requests into valid streams, shutting down other people's connections (although you couldn't be sure you've succeeded). RFC5961 tries to prevent this by adding some cases where the SYN/RST are not treated as valid, but instead it sends a special ACK to the source requesting confirmation. To avoid denial of service, these special ACKs are rate-limited to 10 per 5 seconds. Note these special ACKs are only generated if the SYN or RST look "nearly" valid based on the sequence number, otherwise the RST or SYN is ignored.
And that's what they discovered is the problem--open your own connection to any Destination which has long-term connections (and they picked a USA Today website, but anything would work), and every 2 seconds try to get it to generate those special SYN/RST ACKs. If it's not under "attack", you'll get your ACKs.
Then, spoof billions of packets using a chosen source IP address (and loop through all sequence nums and port nums) and guess the dest port (say, 80).
Now send a little traffic to the Destination on your valid connection to try to get these special SYN/RST ACKs. If you don't get your ACKs (due to the global rate limiting), then you "know" that you've stumbled upon a valid combination of Source IP/port and Destination IP/port and sequence number, so you know who's talking to the Destination machine. If you've picked a Source Address and port number not connected, then these special ACKs don't get generated, so your slow traffic generating these ACKs will not be rate limited, so you can tell this Source IP/port are not connected to this destination IP/port.
So RF5961 turns a pesky annoyance bug into a bug where its possible to determine who's connecting to a particular website (although time consuming).
With more care, they then figure out the sequence number--and once you have that, you can do targeted data injection. (It's always possible to do blind data injection, but the chance you can accurately inject javascript is hard since the sequence number is hard to predict).
RFC5961 should not do global rate limiting--it leaks important data.
It's not a Linux bug, but a buggy RFC implementation. Please read TFA and then try to resume your lame trolling against OSS.
Does WIndows, FreeBSD and OSX implement RFC 5961? Looks like the vulnerability lies in the specs and not in the implementation.
If a hacker injected a story into USAToday that was total BS, would anyone notice the difference?
No, they don't. And they are completely vulnerable to the attack RFC 5961 is meant to avoid.
FreeBSD supports partial implementation of 5961. As well as one of the authors of the RFC for 5961 being a FreeBSD committer. FYI. I have yet to see a Security Advisory for FreeBSD yet about this issue. So time will tell. But so far only Linux is affected.