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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2answers
1k views

Deleting users with nologin shell

On a security audit performed on our production Linux servers , we were asked to remove nobody user if no application are using it. I checked and could see that there are no files owned by 'nobody' ...
6
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2answers
813 views

Why did SDF switch from NetBSD to Linux?

I personally don't have much experience, but I was reading about SDF, and at one point the article mentions that SDF migrated to Linux in 1997, but due to the large number of malicious attacks it ...
6
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1answer
1k views

Security of an encrypted (dm-crypt & LUKS) Ubuntu 12.04 installed by somebody else?

Suppose I want an Ubuntu setup (let it be 12.04) with full disk encryption. Ubuntu offers this as an option during installation. Suppose also that I have somebody (e.g. my vendor) else set this up ...
6
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2answers
835 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 ...
6
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3answers
527 views

Why are web servers traditionally started as superuser?

Thinking about a future web server setup, it struck me that for some reason web servers usually start as root and then drop certain rights (setuid) for the worker processes. In addition there is often ...
6
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2answers
289 views

Lock some accounts during some time periods

Is it possible to lock some accounts in order to be accessible only during specific time periods? For instance the account joe should only be accessible during office hours.
6
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1answer
10k views

How to check if port forwarding is enabled?

I have just set up a DNS server for my own network, and many guides online suggest to make sure that port forwarding on port 53 is not enabled. The thing that is not clear to me is this: should I ...
6
votes
1answer
620 views

Are Debian- and RedHat-style repositories compromised by Heartbleed OpenSSL bug?

The Heartbleed exploit (CVE-2014-0160) makes SSL connections using OpenSSL vulnerable to private key leakage. Does it mean that official update channels in RHEL/CentOS/etc. and Debian/Ubuntu shall be ...
6
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1answer
272 views

Does fail2ban offer any additional protection to SSH if password login is already turned off?

I’m setting up a Debian VPS on Linode to use as a public web server, and I’m following their security suggestions. The last suggestion they make is to install fail2ban, to avoid dictionary attacks on ...
6
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1answer
2k views

Disable random memory address generation in my programs

I'm reading "The art of exploitation" and would like to try some experiments, including reading from and writing to various memory address. I've created some simple programs and trying to overwrite ...
6
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3answers
2k views

BCRYPT - Why doesn't the Linux Distributions use it by default?

Does OpenBSD use bcrypt by default? Why doesn't every modern Linux Distribution use BCRYPT? http://codahale.com/how-to-safely-store-a-password/ https://secure.wikimedia.org/wikipedia/en/wiki/Bcrypt ...
6
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4answers
675 views

How to log into database via script securely?

I am wondering about whether it is acceptable (security-wise) to have database login credentials (user/pass) set in an environment variable or passed in as a command-line parameter? Both of these ...
6
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2answers
754 views

Can a user brute-force a directory listing without having read permission on the directory?

I noticed that when a user is working in a directory to which he does not have read permission that using cd produces different error messages, depending on whether or not a subdirectory exists: $ ls ...
6
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1answer
884 views

/etc/passwd sql with bash access

I just got a CentOS VPS and was reviewing the passwd file and saw this: mysql:x:498:499:MySQL server:/var/lib/mysql:/bin/bash Is bash necessary for mysql?
6
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2answers
1k views

Optimize performance for encrypted disk

Recently I tried to copy 200GB to a 1TB external / USB2 / encrypted disk and it took 36 hours. The same copy when the disk was not encrypted took no longer than 1 hour. I am using dm-crypt (LUKS) ...
6
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2answers
2k views

Why is mount.cifs not installed suid by default?

I am using Gentoo, and on my machine at least mount.cifs is not installed suid root by default. In particular, this means that I can't use the user mount option with CIFS shares. I noticed that ...
6
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1answer
2k views

Lock screen w/ slock after a certain time?

I am running OpenBox in Arch Linux, how can I set it up so that I can have slock lock my screen after a certain amount of time (with no activity)? Thanks!
6
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1answer
57 views

Can someone give an example as to why I'd want to induce a kernel panic using auditd?

We recently implemented some auditd rules in response to an external security audit. My colleague offered some input on them and suggested adding -f 2 to /etc/audit.rules. I can't think of an instance ...
6
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1answer
280 views

How safe is sudo when running from root to run an application as a less privileged user?

Lets say I am logged in at a root terminal and I run something like the following command: sudo -u '#1000' dbus-launch chromium Are there any potential security issues I should be worried about? ...
6
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3answers
4k views

How to prevent command injection through command options?

I have an wrapper application where I need to let the user specify custom options to pass to a simulator. However, I want to make sure the user doesn't inject other commands through the user options. ...
6
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1answer
1k views

Save password in bash script for multiple queries

I would like to know if there is a safe way to only be queried for a password once in a custom bash script, and then save it somehow to be used for later needs. At the end of the script it should be ...
6
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2answers
218 views

Linux graphical password dialog trick security

When we run a command by sudo, the password is asked [sudo] password for user If the sudo is not typed the password should not be asked. If asked, I would assume it as a fraud by the application. ...
6
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1answer
133 views

Send only one warning when the private key is not available

For added security, I would like to require a private key to use sudo on my Ubuntu Server box. I've added private key authentication for sudo as described at ...
6
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1answer
381 views

Any random password results in successful login on tty

I can login to my machine (FreeBSD 9.1-RELEASE) for any user (for example: root or operator or any that exists in /etc/passwd) with any random password that I type... I tried to reset password for ...
6
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2answers
2k views

Hide processes from other users based on groups (under Linux)?

Is it possible to configure process hiding for certain user groups under a linux system? For example: Users from group X should not see processes owned by users from group Y in ps/top or under /proc. ...
5
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6answers
702 views

What is the threat of a user trying to sudo without permission?

I was sshing into a certain computing system that I use. I was trying to follow some Linux instructions that involved sudo, and tried a few times to enter the password unsuccessfully, before realizing ...
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4answers
1k views

How sudo/root-ness detection works

Programs that make changes system-wide require sudo unless I am already the root user. Now, the question is: how exactly does the system figure out that I am (not) root? Does it: Check to see if ...
5
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3answers
2k views

Stracing su and ssh shows the password. Is this a security flaw or am I missing something?

I'm currently fascinated by strace so, being new to it, I decided to play around a little. As suggested by the question title, I tried both strace su and strace ssh. Both commands displayed the ...
5
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2answers
500 views

How are mutually untrusted app's files protected in Linux

I am running a Ubuntu Linux machine. When I run applications written by different vendors like Chrome and Firefox, I notice that they all are running with my uid. But if that's the case, any file they ...
5
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2answers
2k views

How to check which SSH keys are currently 'active'?

How might one check which .rsa, .pem, and other files are 'loaded' or 'active' by ssh-add? I just had this scare: $ scp -i /home/dotancohen/.ssh/dotancohen.pem someUser@1.2.3.4:~/files.tgz . Warning: ...
5
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1answer
594 views

Linux Server Hacked

I received e-mails from Google saying that my websites are hacked. This is the e-mail. Dear site owner or webmaster of domain.com (I received this email for my other domains too), We recently ...
5
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4answers
10k views

File permission execute only

How can I set file to be executable only to other users but not readable/writable, the reason for this I'm executing something with my username but I don't want to give out the password. I tried : ...
5
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2answers
882 views

make a 2nd root?

I was thinking, maybe i'd like to disable passwords for the root user and only use keys to log in. and if i need to login without keys have a 2nd user that is like root in everyway except has a ...
5
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1answer
12k views

What audit log files are created in linux to track a users activities?

One of the machines on our networks was consuming a large amount of Internet bandwidth. However no user was using the system. When I connected to the server using SSH and ran who it showed that a ...
5
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1answer
1k views

root owned program with setuid bit on

Ping is a a program owned by root with the user id bit set. $ ls -l `which ping` -rwsr-xr-x 1 root root 35752 Nov 4 2011 /bin/ping As I understand it, if a user runs the ping process, then the ...
5
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3answers
395 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 ...
5
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3answers
2k views

Hidden Files&Directories in user's home directory [closed]

I am in my user's home directory, I do: ls -a Then it shows me large number of hidden files and directories in my user's directory. Which of them I am allowed to remove? Which ones are necessary ...
5
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5answers
3k 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 ...
5
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2answers
576 views

Writing a “telnet server” type program that uses SSH instead of telnet

So people have written server programs using telnet in which the user simply does telnet server.com and this connects them to the server program, which then provides them with a textual program they ...
5
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2answers
127 views

Is it more dangerous to connect to the net as root?

If I make some kind of tcp connection to the net as root, is that less safe then making the same tcp connection as a normal user? I have been suspecting for a while that by making a connection as ...
5
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3answers
6k views

what is OS hardening in linux or unix?

The term OS hardening itself is misleading/vague to me as i am reading to understand it online here. It seems to me that its something related to making linux/unix box more secure.
5
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3answers
217 views

I'm moving up from managed hosting to a VPS. What do I need to know?

I'll be starting to use a VPS for my web hosting this week, which is a big step-up for me since I've only used managed/shared services before. I've a bit of experience with Linux and I'm not afraid of ...
5
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3answers
526 views

Unix users, groups, and permissions

I don't understand unix users, groups, permissions, etc. For example, things managed by the chmod, chgrp, usermod, groupadd, etc. commands. How do all these things work?
5
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3answers
3k views

How to clear terminal after logging out?

Currently on my laptop when I log out I can still see traces of my last activities (in tty). How can I tell it (Gentoo) to clear the screen before logging out?
5
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4answers
372 views

Is it possible to use pendrive as key for Linux system

I want to give high security for my linux box. So i planed to use my pen drive as key for my linux box. How can i do it ?
5
votes
2answers
464 views

Why ssh-agent group ownership is not root

Trying to understand why ssh-agent has sgid bit and found this post ssh-agent has sgid I have another question, why the group ownership of ssh-agent is nobody not root? What is the reason behind it? ...
5
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2answers
1k views

Process in user mode switch to kernel mode. Then the process will have root privileges?

According to http://www.linfo.org/kernel_mode.html in paragraph 7: When a user process runs a portion of the kernel code via a system call, the process temporarily becomes a kernel process and is ...
5
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7answers
539 views

Are there additional ways to protect SSH connections besides firewall and RSA Keys?

Sometimes I don't have a static IP and need to administrate my web server remotely. I'm looking for any additional layers of protection I could add to make opening port 22 safer. Currently I have ...
5
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2answers
2k views

Preventing access to TTY when X is killed

Assume I start an X server manually from a virtual console /dev/tty1 with xinit or startx, with the line id:3:initdefault: set in /etc/inittab. The X server gets run and put on another virtual ...
5
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2answers
149 views

Permissions depending on how you login: ssh/su/sudo

As user I have access to a remote linux machine where I can: sudo su - other_user Among other things, this allows me to add my own public key to authorized_keys for other_user, which effectively ...