Skype Linux Reads Password and Firefox Profile

mrcgran writes "Users of Skype for Linux have just found out that it reads the files /etc/passwd, firefox profile, plugins, addons, etc, and many other unnecessary files in /etc. This fact was originally discovered by using AppArmor, but others have confirmed this fact using strace on versions 1.4.0.94 and 1.4.0.99. What is going on? This probably shows how important it is to use AppArmor in any closed-source application in Linux to restrict any undue access to your files."

Comments

Shadow passwords FTW

[strredwolf]

This is why you should have shadow passwords, so that your encrypted password isn't stored in /etc/passwd.

Why..

[mikkelm]

.. only closed source applications? I don't think most people read the entire sources of open source applications that they use.

Re:Why..

[lilomar]

Not everyone has to, just one person.

When I use Open Source apps, I do so knowing that there are many developers and hobbyists that have looked over the code, so I know that there aren't any glaring security flaws.

Imagine this had been an Open Source product for a minute... instead of an article just saying that it read /etc/ files, it would have said this part of the code reads the files, this is why it is nessasary, or here is a patch to stop it from doing this.

/etc/password

[Colin Smith]

Is a public file, as are virtually all the others in /etc.

What's it doing? Well, what libraries is it linked with? Perhaps it's converting your UID into a name among other things.

What a load of FUD

[arivanov]

Dunno about AppArmour, but there is no way in hell to distinguish between legitimate getpwnam, getpwuid, etc calls and reading the whole passwd file on a linux system using strace.

Example:

strace on ls -laF immediately gives

open("/etc/passwd", O_RDONLY) = 4

Followed by quite a few reads out of it. So by the logic of the poster ls -laF is a horrible application doing horrible things to your system.

Unless you have read the source or single-stepped trhough the app with a debugger, examined the data and found that it does something nefarious like sending skype the whole of your /etc/passwd you should not claim that it does something illegitimate.

Re:What a load of FUD

[DavidTC]

Um, because it wanted to refer to you as using real name, which is the entire damn point of having the field in /etc/passwd? Or even your username?

Without looking in /etc/passwd all it would know is your UID.

Or perhaps it's not even the thing doing it, perhaps it's using a shell script to see if the skype: handler is registered in Skype, and that script does 'ls -l' to check file sizes.

What I'd be interested in figuring out is exactly the fuck confidential information people think is hanging out in /etc/password? We all know that there are actually no passwords in that file, right?

And everyone know that programs access it all the time, right? Which is why it's deliberately world-readable?

Seriously, this entire article was made by someone who knows how to use strace but hasn't bothered running it on other programs, and has no idea what /etc/passwd is for.

Re:What a load of FUD

[mysidia]

This article looks like guerilla advertising for SuSE/AppArmor, a Novell product.

It's a fine example of why people who don't understand the C Library and Linux/BSD/POSIX SDK and how to disassemble the application should not be relying much on AppArmor to tell them what's good and evil.

The trouble is the library does it, not the application, and a few reads of some files can't tell you the application's intent, or show whether the information is being encrypted and sent out to the software maker or not.

This reminds me of folks that spend day and night reading firewall logs and mailing out hundreds of complaints to networks if a host so much as pinged them or tried to make a port 25 connection.

Sure, they could be a spammer or hacker, but just because you set alarms -- a connection attempt doesn't say that anything evil is being attempted. I'd be far more concerned if someone said Skype read something from /etc/shadow, then the very next thing it did was to make a port 80 connection to Skype's servers and send a HTTP POST submission with lots of binary jibberish.

Any program that needs to do so much as lookup the user's shell, home directory, username attribute, or real name needs to examine /etc/passwd.

Most non-trivial applications need the user's home directory to load their user preference files. Some internal shell script of Skype may even need the user and group names, in order to establish appropriate file permissions.

Sure, there are environment variables that popular distributions' shells use; however for an application like Skype to be portable, it may not be able to rely on a particular environment variable like 'HOME' being set -- it may be safest just to getpwuid() the user and lookup their home directory that way.

In any case, the SOFTWARE DEVELOPER would have the option of using getpwuid() instead of getenv("HOME"). It's the developers' choice.

Applications can accomplish things in fairly boneheaded ways sometimes, but that doesn't indicate anything malicious or evil.

Re:Flawed logic

[DaleGlass]

First you assume that the person(s) that read it would catch anything evil in it. It's not like the evil code is necessairily going to be in a function called doEvil(), it could be very cleverly hidden among legit functions so that most people would miss it. With good obfuscation it wouldn't be hard to make something that people would have to play with a debugger just to figure out what is going on, and as such miss it on anything less than a really intense code audit.

This sort of "evil" is very transparent. You can code a hidden buffer overflow/exploit/backdoor in such a way that it's not obvious (= instead of == for example, caught in the Linux kernel once). But how do you hide an access to say, /proc/interrupts? You need to spell out the filename, and there's got to be an open or fopen for it somewhere. Any attempt to encode the filename is going to be weird and suspicious. Plus, file parsing would be quite a bit than a single line of code, so it's hard not to notice something is being read, stored, etc.

Second, you assume the people who look at it aren't in on it. So maybe a couple people look at the code and find the evil bits. They contact the developer and ask what's up. The developer then lets them in to his cabal, who can use the evil bits for their own ends. The people decide they like this and don't tell anyone. The people who read the code have to be honest for this to work.

Uh huh. Such a thing would be an outright admission of evildoing. Depending on what is being done it might be enough for a lawsuit, and definitely enough for mass publication all over the web to ruin the developer's name. Slashdot had a story on some Mac developer who claimed there was an anti-piracy check that'd delete the user's documents folder. Just the claim (which the developer says wasn't real and intended to scare people off) resulted in such outrage he's probably unemployable for years now.

No, anybody with any brains would deny any wrongdoing and claim a hacked server, or pretend that no mail is arriving at all.

Fourth, you assume that the binaries are the same as the source. I'm betting at least some of the time, and probably more often than that, you install things from a binary package. It's easy and much faster than compiling everything. Great, but how do you know the source follows the binaries? It would be easy to release an untainted source, and then tainted binaries. That the checksums differed wouldn't be of any note, since it could just be that different compile options were used, or even a different compiler (for example using ICC since it generates more efficient binary code). As such no source audit would ever turn up the problems.

But 99% of Linux software is delivered by the distribution, with the package maintainer often being completely unrelated to the developer. While it's not impossible for something weird to be going on, those distribution maintainers do things like patching the source and dealing with its bugs. You can bet that eg, the Debian maintainer of Firefox looked at the source.

Finally, even if you compile your own, you assume that nothing else is in on it. I'll refer you to the classic Ken Thompson story http://cm.bell-labs.com/who/ken/trust.html. Some other program, and not just the compiler, could be in on inserting a trojan. It might never exist in source form, yet always get compiled in. Thus even a build from a verified source isn't a defense.

That's a tricky one, but you can use a different compiler. Compile gcc with icc for instance. For OSS I think this approach is unlikely due to the frequence with which somebody decides "let's rewrite this part". It's easy to make a compiler that hiddenly changes some well known part of the source, but it's much harder to deal with a complete reorganization of it. To keep it up would need updates