Content related to computer security., i.e. content about policies, mechanisms, etc. needed make sure data is not leaked or corrupted and services available in all circumstances.

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25
votes
2answers
60k views

What user should apache and PHP be running as? What permissions should /var/www files have?

I just spun up an Ubuntu 11.10 box and then ran apt-get install apache2 php5 to install apache2 and PHP 5 on the box. Now it is functioning as a "web server" and it loads the "It Works!" page. Now I'm ...
4
votes
2answers
3k views

Hardening debian?

So I have thought a bit about hardening a Debian squeeze file & VPN server lately. Right now, we've placed the machine behind a firewall only allowing SSH connections from LAN, set a strong root ...
-3
votes
4answers
478 views

Since Android has malware, does it mean no Unix is immune from malware?

Android has virus: Android.Counterclank, Android.Tonclank (seal info, back-door). Does it prove that FreeBSD, Solaris, Fedora, CentOS, ArchLinux, Ubuntu all is running and having similar ...
12
votes
4answers
2k views

Why do we need a firewall if no programs are running on your ports?

When I try to telnet to a port on a server, and if there is no program listening on that port telnet dies with a "Unable to connect ... " error. I understand that. But, why do we need a firewall if ...
5
votes
3answers
328 views

Preventing binary planting attacks in Linux

If a user account on a Linux machine is compromised, clearly, all files owned by that user are compromised. Unfortunately, if the compromised user also has sudo privileges, it seems that binary ...
9
votes
5answers
6k views

Shell Script mktemp, what's the best method to create temporary named pipe?

I'm aware its best to create temporary files with mktemp, but what about named pipes? I have an idea, I'm sure it would work, but I would really like an expert opinion. I prefer things to be as ...
1
vote
1answer
529 views

portsentry and IPTables on constant reboot, but not sure why

I have been doing some hardening on a new server [ centos 5.7 final ] i also have logwatch and seem to be getting these strange logs Commands Run: User root: /sbin/service portsentry restart ...
10
votes
2answers
2k views

Automatic security updates on Debian squeeze server

For a production Debian squeeze server, what are the best practices or recommendations for handling security updates? I have seen various articles on cron-apt, apticron, unattended-updates, apt cron ...
2
votes
1answer
108 views

Fedora15/Gnome3 - Exit elevated priviliges mode

While using Fedora 14 (Gnome2), Each time if I was doing some privileged task (ex - mounting a new hard drive), I would be prompted for password and then there would appear an icon (like keys) on the ...
5
votes
5answers
2k views

Why is it recommended to create a group and user for some applications?

Most of the time, when installing a program from source it is recommended to create a new user and a new group and give /usr/local/<myapp> the recently created user and group ownership. Why is ...
19
votes
3answers
6k views

Why does the 'bin' user need a login shell?

During an audit of /var/log/auth.log on one of my public webservers, I found this: Jan 10 03:38:11 Bucksnort sshd[3571]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 ...
8
votes
9answers
13k views

How do I write a test for system login?

I've written a Python CGI script that invokes bash commands, and it needs to test for a successful login on the host. How do I write a test for that? For example, could I create a bash script that ...
2
votes
1answer
112 views

What commands should be run when retiring a remotely hosted server?

I have a dedicated server from a friendly host located a substantial distance away from me, so the only access to the machine is SSH. It's a month to month deal, so I don't own the hardware. I'm ...
3
votes
1answer
246 views

sandbox tcpdump under OpenBSD?

From FreeBSD 9.0 tcpdump is sandboxed with Capsicum. Are there any solutions for sandboxing tcpdump under OpenBSD? Just want to secure a running: tcpdump -w output.pcap because it can be only used ...
11
votes
3answers
356 views

Prompt user on Linux security denial

Is it possible to make a Linux security module (eg. AppArmor, SELinux etc.) prompt the user, when an application wants to access classified files or folders (digital signatures, SSH keys, credit card ...
2
votes
1answer
569 views

UFW Limit does not appear to work

I have my ssh port changed to XXX. Then I did ufw limit XXX/tcp However, when I try to login, after 5/6 failed attempts I get thrown back to prompt, but I can try again. Is that supposed to be the ...
6
votes
4answers
3k views

SSH authentication: either SSH keys or one time password

I have an Ubuntu 10.04 Linux server that I normally ssh into (from my home machine) using ssh key authentication. However, sometimes I need to ssh remotely from potentially insecure machines (like ...
2
votes
3answers
3k views

Making sense of auth log

I am seeing some log enties that look like hacking attempts Type 1 Dec 26 03:09:01 ... CRON[9271]: pam_unix(cron:session): session closed for user root Dec 26 03:17:01 ... CRON[9308]: ...
9
votes
4answers
611 views

Good practice to use same SSH keypair on multiple machines?

I recently got a new laptop for work, and I was wondering whether it'd be good practice to keep using the same RSA keypair as I'm using on my old work laptop. I'd really like to not have to create ...
4
votes
3answers
327 views

Linux executable sandboxing?

I'm running a service that allows users to submit code which is compiled and executed on the server. At the moment I'm using Moe and while it works fine for C and C++ code, I've been having some ...
18
votes
6answers
19k views

How do I recursively shred an entire directory tree?

I have a directory tree that I would like to shred with the Linux 'shred' utility. Unfortunately, shred has no -R option for recursive shredding. How can I shred an entire directory tree ...
4
votes
2answers
717 views

How can I use Skype with lxc?

Under Scientific-linux? https://en.wikipedia.org/wiki/LXC I just want to separate Skype, because I don't trust it. We are using it only to call/chat with people, no file transfers!
9
votes
3answers
10k views

How can I track who SSH'es into my linux machine?

I'm running Ubuntu 10.04. Is there a way I can get a daily report of who has logged onto the box, what time, and even - this may be asking too much - a report of the commands they used? This is a ...
2
votes
1answer
857 views

Deny external SSH access to a user

Is it possible to deny access to a user (in my case www-data) from outside the network? Or possibly deny this: ssh www-data@example.com But allow this if already logged in: su www-data
3
votes
2answers
640 views

If you SSH into another computer, how to access other X displays?

This is a query based on personal use. A troll in our local network had downloaded Crikey, the key-event simulator. He used it to simulate events on other computers, leading to unwanted things. For ...
1
vote
1answer
198 views

How 'safe' is it to use new distributions of linux? [closed]

I hope this is the right place to ask this. I was looking at some new distros of linux that came out fairy recently and I really like their UI. I want to start using one of these but I'm a bit ...
2
votes
1answer
872 views

Debian + Nginx/Unicorn permissions

Is there a security risk in running a web server like Unicorn as root? The Nginx master process runs as root, the Nginx worker runs as the limited www-data user, but I can't set another user like ...
4
votes
2answers
508 views

Is it possible (and a good idea) to do `pw lock root` on FreeBSD?

I have set up sudo on my FreeBSD server. As I now never want to log in as root anymore, I was wondering whether I should do sudo pw lock root. My questions are: Is this possible, without forever ...
-1
votes
3answers
568 views

no root shell freely available sudoers policies

I want to prevent users who need escalated privileges from obtaining any kind of a root shell. However since there are many ways to attain this, and many non root commands ( like those found in ...
8
votes
2answers
150 views

Signing/Checksumming the kernel to prevent/detect manipulation

All my partitions are encrypted (/ and /home), but the /boot partition has to remain unencrypted and is open for manipulation. I was thinking about hashing the kernel on bootup and checking the result ...
28
votes
4answers
1k views

Execution of possibly harmful program on Linux

I'm writing a program that will test programs written by students. I'm afraid that I can't trust them and I need to make sure that it won't end up badly for the computer running it. I was thinking ...
5
votes
1answer
265 views

How can I find a Ubuntu package to use with Amazon EC2?

I'm looking to set up a new server on Amazon's EC2 and I wanted to use Ubuntu 11.04 is it is fairly new but not too new. I previously used 10.10 which I think is also very stable and time-tested. My ...
3
votes
3answers
334 views

Setting execution right to whole directory - is it good or bad idea?

I have a zip file containing lot of files and directories for a certain application which should be running on Linux. Some files needs to be set as executable, but the zip file format afaik does not ...
2
votes
1answer
2k views

Encrypt files using gpg (and them symetric encrypting the key) - is it a normal thing to do in the *nix world?

I read a lot of articles about using gpg to encrypt email, but I would like to use it to encrypt some files - mainly a bunch of *.isos. I'm going to describe what I thought I would do, so you can ...
1
vote
1answer
515 views

LoJack protection and recovery for Unix/GNU/Linux running systems?

The LoJack theft protection and recovery system looks very impressive, especially that they will find and return your computer for you, but the software is for Windows and OS X only. Is there an ...
3
votes
1answer
156 views

how to disallow user to change process group

Is it possible to restrict a process from changing it's process group? For example, user nobody seems to be able to call setpgid(0, 0) which sets process group of current process to pid of that ...
2
votes
2answers
304 views

How to deny rdesktop access to others?

Someone keeps trying to connect to my Ubuntu machine through remote desktop. Is there any way I can determine who it is, and permanently block access to my machine?
0
votes
1answer
944 views

How to find out that someone is using a Keylogger on the machine I am using?

HW/SW/whatever keyloggers are there. How to find out? E.x.: Regularly check the cable of the keyboard, because there could be HW keyloggers: http://i.imgur.com/TeMwo.jpg But what about other HW ...
5
votes
1answer
881 views

SSH Public key comment separator

I've created a SSH authentication key (with ssh-keygen) in two different servers, both with a useful comment, but the public key of one server has == between the key and the comment, while the other ...
8
votes
2answers
5k views

How to check, which limit was exceeded? (Process terminated because of ulimit. )

Let's assume process runs in ulimited environment : ( ulimit ... -v ... -t ... -x 0 ... ./program ) Program is terminated. There might be many reasons : memory/time/file limit exceeded ; just ...
1
vote
2answers
404 views

Is there file format for checksums?

I want to store SHA512 checksum of the file for my application. How to do it in common (popular) way? So this checksum can be used but by third party application too.
1
vote
1answer
625 views

rpc.statd and avahi-daemon listening on all networks?

Background: - I'm running a home Debian GNOME desktop connected to the internet through an ethernet cable to an ethernet router. - I have a printer connected directly to my PC with a USB cable. - My ...
0
votes
1answer
2k views

How to really security a linux-mint-desktop?

I'm installing some security software in my mint9Gnome. I first went to Firestarter and looks like a pretty start. Now I'm going to OSSEC and want some good tools to search my logs too. Thinking ...
4
votes
1answer
156 views

Mount and automount and security problems

Are there any security problems related with (auto)mounting device?
2
votes
2answers
1k views

Directory/files owned by a non-existent user

A user has created a directory with files, but the user does not exist in /etc/passwd or /etc/group. The system is a Fedora server with an FTP server and proxy which redirects to a CentOS server with ...
3
votes
4answers
234 views

Internet SSH Server Security Considerations

What steps should I take to reasonably secure my linux desktop before opening sshd to the Internet so I can connect from anywhere?
13
votes
8answers
2k views

How can we limit the impact of ssh probes?

My webserver is constantly attacked by various IP addresses. They try five passwords and then change the IP address. I have done various lockdowns like using ssh-keys and not permitting passwords, ...
2
votes
2answers
1k views

A command to check file access permission for another user

I need to know how to check the effective file access permissions for a given user, but it takes long to do this manually starting from / up to the target file or directory, checking group, ...etc.
4
votes
2answers
3k views

How do you protect a plain text credentials file with the username and password?

I am trying to setup an auto-mounting network drive. The network drive requires a user/pass. In the man page for "mount.cifs" there are two ways to provide the user/pass. [not recommended] put the ...
-1
votes
1answer
12k views

What is sport and dport?

I want to stop internet on my system using iptables so what should I do? iptables -A INPUT -p tcp --sport 80 -j DROP or iptables -A INPUT -p tcp --dport 80 -j DROP ?