Is /etc/shadow safe?

grant123 · Veteran Joined: 23 Mar 2005 Posts: 1080

I'm syncing my laptop with several other identical laptops which are used by other people. Are my own passwords in /etc/shadow safe?

SirRobin2318 · Posted: Mon Mar 03, 2014 5:56 pm Post subject:

/etc/shadow is fine, the hashed passwords are in /etc/passwd-. (not a typo, with a dash at the end).

grant123 · Veteran Joined: 23 Mar 2005 Posts: 1080

My hashed passwords appear to be in /etc/shadow and not /etc/passwd-. Either way, is the file containing them safe to distribute?

SirRobin2318 · Posted: Mon Mar 03, 2014 9:00 pm Post subject:

How did you manage that? Did you purposefully specify that? What is the ownership of that file? Your system may be insecure to begin with...

In any case, no, I wouldn't; http://www.openwall.com/john/doc/EXAMPLES.shtml

grant123 · Veteran Joined: 23 Mar 2005 Posts: 1080

I definitely did not do it on purpose, but it's like that on all of my systems so Gentoo must set it up that way:

-rw-r----- 1 root root 1158 Feb 26 09:55 /etc/shadow

Your link isn't working right now, but is the idea that someone could decipher the password if they have access to its hash?

Are there other files I should not distribute from a security or privacy perspective besides those in /home?

SirRobin2318 · Posted: Mon Mar 03, 2014 9:55 pm Post subject:

Actually, you are right. shadow and shadow- are the same files on my system too... I'll look into that.
But yeah, giving the expected hash to an attacker enables him to brute force the system too easily.

How are you syncing the pcs? just a cp/tar/dd? Same hardware?

To ensure no important info would leak out, I'd take the opposite approach: copy your world file after having done the basic install, emerge @world, then choose important /etc files to copy.

SirRobin2318 · Posted: Mon Mar 03, 2014 10:01 pm Post subject:

OK, so the - version of /etc's group, shadow, passwd files are just backups, I was mistaken there.

grant123 · Veteran Joined: 23 Mar 2005 Posts: 1080

Hu · Moderator Joined: 06 Mar 2007 Posts: 21602

Anything in /etc needs to be given special consideration before syncing. As you know, some files in /etc are security-sensitive. Others may represent system-specific configuration, such as preference on which services to start, how to configure the network, and so on. Identical hardware does not guarantee identical software usage, so even if the files can be shared, that may not be the right choice.

szatox · Advocate Joined: 27 Aug 2013 Posts: 3131

Why you're syncing those laptops?
If you want to save some compilation time, you can use portage to build binary packages and then install them (with portage) on the rest.

SirRobin2318 · Posted: Tue Mar 04, 2014 8:33 am Post subject:

If your concern is build time, look into this instead: https://wiki.gentoo.org/wiki/Binary_package_guide#Creating_binary_packages

As for etc configuration, I keep the files that are modified in a git, and sync that with other PC's etc. I do it with files like /etc/portage, X11.
I'm the user of both those PCs, so I also have sudo, sshd, polkit & firewall rules. Be careful before sharing those, there could be sensitive information in them (mainly if they're badly configured).

666threesixes666 · Posted: Tue Mar 04, 2014 9:30 am Post subject:

http://www.linuxsolutions.fr/annvix-using-the-tcb-shadow-alternative/

http://www.openwall.com/tcb/

i remember seeing something about shadow being compromised a while ago.

http://felinemenace.org/~andrewg/configuring_gentoo_to_use_openwall_tcb/

brew me up a wiki so i can sleep and get drunk instead of fixing it myself.

grant123 · Veteran Joined: 23 Mar 2005 Posts: 1080

666threesixes666 · Posted: Tue Mar 04, 2014 9:37 pm Post subject:

i think tcb is what you're after.... tcb is NOT in portage or in any overlays that i could find. zunga says its sys-auth/tcb like it did have it at one time. x86 x86 x86 maybe its because im amd64 that im not seeing it?

http://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-x86/sys-auth/tcb/?hideattic=0

https://bugs.gentoo.org/show_bug.cgi?id=371167

last comment of the bug says use hardened shadow instead of tcb.

https://code.google.com/p/hardened-shadow/

im not selinux or hardened so idk whats what.... im just digging for info, and sharing what im finding.

Hu · Moderator Joined: 06 Mar 2007 Posts: 21602

vaxbrat · l33t Joined: 05 Oct 2005 Posts: 731 Location: DC Burbs

/etc/shadow and /etc/gshadow for dictionary attacks.

/etc/ssh for the private host keys (the not .pub key files)

/etc/security/opasswd for password history database maintained by pam_unix

Those would be ones I care about in auditd for failed read access attempts. I also care about failed and any successful writes to anything in /etc.

If you run a dns server you will probably want to watch /etc/bind/rndc.key

grant123 · Veteran Joined: 23 Mar 2005 Posts: 1080

vaxbrat · l33t Joined: 05 Oct 2005 Posts: 731 Location: DC Burbs

The keys in /etc/ssh are generated the first time you run sshd on the host and are then used to prevent man in the middle attacks. When you first ssh into another box and get that "I don't know who this is, do you want to continue?" type prompt, its the host keys that are used to figure this out. The known_hosts files that end up in your user .ssh directories contain the public key from that pair for each host you know about.

You probably won't see the opasswd on a default install. It doesn't get needed unless you set the "remember=n" stanza on pam_unix in the password section of the pam system-auth file. It then stores the hashes of passwords that users create when they go through a change password. It gets referenced to rub their noses in it when they attempt to recycle an old password that they've used in the last n changes.

grant123 · Veteran Joined: 23 Mar 2005 Posts: 1080

grant123 · Veteran Joined: 23 Mar 2005 Posts: 1080

Any opinions on that last one?

SirRobin2318 · Posted: Mon Mar 10, 2014 4:51 pm Post subject:

grant123 · Veteran Joined: 23 Mar 2005 Posts: 1080

Now that I think about it, I'm not sure what the problem is. /etc/shadow is root:root -rw-r----- so other users can't read it. Is the danger someone booting a USB stick and reading the file that way?

SirRobin2318 · Posted: Mon Mar 10, 2014 7:12 pm Post subject:

Yes, of course that's a problem. They might even get root access in other ways. They could boot in single user mode. They could exploit a future vulnerability that will be documented in glsa.
We told you it's a bad idea, why are you insisting? At this point, just do what you want.

If security is an issue, you shouldn't be doing this. Separate /etc's, just use binary packages. If you're doing this to share with trustworthy family and friends, sure, why not, but then security isn't an issue.

grant123 · Veteran Joined: 23 Mar 2005 Posts: 1080

I'm not only trying to keep my systems secure. I'm also trying to learn about securing them. I appreciate your help but please don't expect me to follow instructions without understanding why I'm following them.

Having said that, thank you for elaborating. Isn't /etc/shadow vulnerable in these ways on every system with user accounts?

SirRobin2318 · Posted: Mon Mar 10, 2014 10:02 pm Post subject:

If you are trying to keep these systems secure you are going about it the wrong way.

Cloning everything and trying to find problematic files is bad. You'd have to know what every file contains. This is not an easy goal. Not only it's not easy but human errors happen, even with loads of experience you would mess up. To limit the amount of information leaking out, you should be taking the problem the other way around: What files am I sure I can share without leaking sensitive data? Sharing everything by default is a Bad Idea.

/etc/shadow has a relatively sane security logic. You could share it and maybe nobody would be able to hack into it. But there are tools that are dead easy to use to exploit any weakness in your choice of passwords. It might take months, but it could work. Why take the chance?