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Getting Hacked Through Your Terminal
hdm writes "My company recently published a paper on security issues with common terminal emulator applications. The interesting thing about these vulnerabiltiies is that many of them only require the victim to be running tail on their log files (apache, syslog, etc) for the attack to be successful. The paper (TXT) can be found here."
Most exploits that existed over 5 yrs ago are still valid.
For instance, you can recover a root password in just 10-15 minutes on ANY machine.
31 people regularly point & click my G-spot
However, certan software would allow an attacker to insert these control codes anywhere, and not just interpret them from the menus.
Imagine the hilarity that insues once the attacker figures out the embed sequence for the drop to DOS feature.
The more you know, the less you understand.
The idea is probably to give a scenario so those weak on imagination have something to use to show their boss to explain why they should spend time on this issue.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
Apparently the OSX terminal might be susceptible to this. It is possible to alias different escape sequences to commands like lm and ll to make the terminal full screen, send it to the background, make it tall, etc.
/var/log/messages, but I won't be the one to find out as my PowerBook is in the shop...
It would be interesting to see whether actual commands can be executed if tailing
Back in the day, "Ansi Bombs" were considered an art form. With the art scene so active, you could usually embed some evil escape string in a good looking graphic and know that you were going to get people.
The problem was DOS' overly-powerful ANSI.SYS interpreter. It let you remap any key to an arbitrary set of keys, making keyboard macros pretty easy. However, it also let evildoers remap "Space" to, for example, "del *.*, enter, y, enter." Luckily, there were third party ANSI interpreters that didn't suffer this vulnerability.
One time, when I was about to reformat my HD, I even wrote an ANSI bomb to do it. Crazy stuff. There's an interesting (and of course, old) paper about it here.
It all goes downhill from first post
So they discovered ANSI bombs over again.
Looks like it.
I recall the "ANSI Standard Trojan Horse" (though it was misnamed). It became quite common after ANSI standardized a cross between the VT100 and Ann Arbor Terminals escape sequences.
Simplest form was to send a "talk" mesage to a root user containing an escape sequence that programmed a hotkey with your command-to-be-run-as-root and then "hit the key" by remote control. (You could even bury it invisibly in an otherwise innocuous-looking message.)
ANCIENT stuff. What-early '70s?
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
Some years ago I managed to make an xterm dump core simply by typing the contents of a binary file, which did not contain any malicious data, it just be coincidence contained a byte sequence that would cause xterm to dump core. Investigating this I found, that some sequence of 24 bytes was responsible. But if I made the xterm window larger, it would not crash from this sequence, however it turned out the original file contained another longer sequence that could also make a larger xterm dump core. I never actually understood exactly what was going on, but I found that later xterm versions does not crash from the sequences I saved from back then.
Do you care about the security of your wireless mouse?
A long long time ago, on a uucp-net far, far, away, we didn't use terminal emulators, we used real hardware terminals. Most of them didn't run ANSI (I don't remember if the ANSI terminal standards were defined yet, but they looked very much like a DEC VT-100 terminal), but that meant there were lots of types of terminals, all trying to achieve market differentiation by having cool features or small size or large screens or cool plastic cases. Lots of different cool features means lots of vulnerabilities. The hackers in question had REDISCOVERED AN OLD TECHNIQUE - they found ways to hand escape sequences to VT100 terminals that would get the terminal to send arbitrary text back to the computer, which in those good old command-line days meant they could do anything they wanted. All you needed to do was email somebody a message with carefully crafted character strings in it, or use the talk program to write them to their terminal (back when everybody left their ttys writeable so talk would work.) Some of the popular techniques were to abuse programmable function keys (send a sequence to put some string in F1, then another sequence to auto-trigger the F1 key), or automatic whoami-responders (VT100 had one of these), or put the terminal into loopback testing mode (letting you type anything you want.)
The Hewlett-Packard HP2621 and its relatives had two easy things to do, which didn't let you send arbitrary characters but still hosed the user - one did a reboot on the terminal (and thereby dropped the connection), while the other put it into test pattern mode (sending a long string of UUUUUU to the computer.) There may have also been some block-mode things that let you send arbitrary characters to the computer, but these two were the easiest and best-documented. A couple years later, when I was a newbie learning Unix programming and security at Bell Labs, and Robert Morris Senior (father of RTM the Worm Author) was a department head for computer security (before he went to NSA), we'd had a discussion about some techniques I was trying (which he cracked through personally :-), and a few days later, when I'd patched those holes, I was playing rogue in the evening, and one of his people talked the test pattern sequence at me. For a few seconds, I though Umber Hulks were suddenly going to eat my character, but then realized I'd been hacked, and it was one of RTM's people following up on what I'd patched and what I hadn't...
Terminology note on "hacker" as opposed to "cracker" or "vandal" - The folks at Berkeley really were hacking - tinkering with things to find their limits - and while they could potentially use their knowledge for evil, they instead told people about it, which reminded lots of us to check for potential security holes in our systems.
Bill Stewart
New Fast-Compression-only CPR http://preview.tinyurl.com/dy575ks
I'm very impressed with the intelligent and humble discussion that is in that thread. They really are both trying to work out how to avoid the problem without breaking applications, rather than blamestorming or pretending it's not an issue.
... and glad I use konsole, at least until a bug is found there ;)
Michael Jenning's comments that he's not an expert on security, but does try his best show a real sense of humour and concern for his users.
Ok, so I'm being a bit of a fanboy, but most links to discussions between open-source developers I see these days are the fights they have (on the very public mailing lists where we can see them). We tend to forget the good work they do the rest of the time.
(raises hat, or would if I was wearing one)
Thanks. :)
I started out my life on Unix as a sysadmin, and I always found it distasteful how software developers would get all pissed off at the people who reported the vulnerabilities, as if they were somehow to blame for the author's own screw-ups.
The bottom line is simply that the person who wrote the code is responsible for their own mistakes. That's really where the buck stops.
In the end, all that really matters is that things get fixed as quickly and correctly as possible for the sake of the users. Ego-sparring and public feuds accomplish nothing and are ultimately counterproductive.
Michael Jennings | HPC Systems Engineer, Lawrence Berkeley National Lab | Author, Eterm (eterm.org)
Larry Wall's famous quote says Great Hacker virtues include Laziness, Impatience, and Hubris.
I would agree, and say that a Great Hacker would locate those killer ctrl codes, get a boatload of diagnostic information together, and hand all that over to the maintainer of the terminal program and then not sweat trying to figure it out themselves.
Let someone that knows the code, and might be better able to divine what's up have a wonk at it. You could even check the diffs if it ever gets patched, and you were curious and had time to kill.
Then, the Great Hacker would go and patch their own project to fix up the newest incoming bug report.
Then, the Great Hacker would rest and eat of the Divine Pizza.
And all would profit.
Keep your packets off my GNU/Girlfriend!
Some programs or setups spit stuff out to the console - warnings, error messages etc.
I remember doing something similar when testing my company's TIS FWTK setup years ago. When you used an address with unbalanced brackets, sendmail when called by smapd will grumble to the console. As a test I sent an email with a ESC sequence setting the foreground colour to black and it worked. Wasn't too surprised. Wasn't able to find an exploit for the console term at that time, and no one abused it (security through obscurity).
Later I switched to using qmail (IIRC qmail 1.0.3 dates to 1998, the TIS FWTK has been around for quite some time). Just to test things out I also recently wrote an smtp proxy to enforce state and filter out stuff(qmail may be robust, but it tends to pass the junk unfiltered to other stuff which may be less robust).
Some O/Ses send a many kinds of messages to the console too.