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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md5 password hash

I'm looking to create a md5 hash to use in /etc/shadow. Someone suggested using grub-crypt. Every time I put the same password in I get a different hash. [root@endpoint ~]# grub-crypt --md5 Password: ...
2
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4answers
64 views

can a super user steal passwords from other users with keylogging?

First, before I get answers containing information that I already know, yes, I'm aware that the superuser can reset passwords, and yes, I know that the superuser can log in as other users without ...
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2answers
38 views

Is this an argument that Linux security is not impenetrable?

From what I understand, the biggest and probably only line of defense against unauthorized software (viruses and worms) from being installed on the system is to simply not allow it unless an admin ...
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3answers
58 views

Is linux secure? [duplicate]

Is linux free from almost all security vulnerabilities when compared with windows? If there are so, can i install any patches to fix them? Thanks in advance.
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1answer
396 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 ...
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1answer
21 views

Can I use the sudoers function without enabling the suid bit?

I mounted all my FS with nosuid option and removed the suid/sgid bit from all my files. The question: It looks like I breaked sudo. It doesn't work anymore, no matter what I try to set in ...
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1answer
145 views

Why is “nodev” in /etc/fstab so important? How can character devices be used for hacking?

I am learning about linux security and struggling to understand why a USB stick with a character device on it is potentially dangerous. If I have a USB stick with a bash executable that has setuid ...
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3answers
489 views

How do I explicitly and safely force the use of a built-in command in bash

There's a similar question that deals with the 'wrapping' scenario, where you want to replace for example cd with a command that calls the builtin cd. However, in light of shellshock et al and ...
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2answers
50 views

Chroot user exit jail [duplicate]

I am using OpenSSH chrootdirectory feature to give access to a user via ssh. Can this user exit the jail and return to the normal OS environment? Maybe with su?
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1answer
78 views

CRON session entries in logs

I'm having this in my RaspberryPi /var/log file Feb 26 21:17:01 raspberrypi CRON[15182]: pam_unix(cron:session): session opened for user root by (uid=0) Feb 26 21:17:01 raspberrypi CRON[15182]: ...
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2answers
89 views

How to get a grsecurity kernel on Debian Wheezy using the linux-patch-grsecurity2 package?

There is a package linux-patch-grsecurity2. But it seems to be lacking documentation. How to make use of linux-patch-grsecurity2 to get a grsecurity enabled kernel?
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1answer
35 views

Different password for login and sudo - security concerns

I'm planning to follow the steps described in this answer to have a different password to log in and sudo. The reason is that I want a high security password to access my account or unblock the ...
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1answer
52 views

Throttle accounts after failed SSH login attempts

I have to set up a server that will allow remote logins. Obviously security is an issue. In this first pass we are discussing:- Locking a person for 15 minutes if they fail to login correctly three ...
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1answer
44 views

How to set up users, ownership and permissions across local and remote servers?

I've been learning the Linux OS over the last year or so and I am still very confused on how permissions vary from different configurations. I am trying to set up my local development environment and ...
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2answers
24 views

Protected archive (7z, RAR, Zip) open at a specific time

Are there any compression tools that are unopenable or password-protected until a specific time, at when the security is then lifted? Literally an enforced: "Do not open until --/--/----"
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3answers
111 views

how to set up permissions of “download” dir to prevent execution of exploit program

There is a host with a local service that receives data from a remote location (via e.g. http) and saves it locally under /var/log/data/ in some mydir. $ ls -al /var/log/data drwxr-sr-x+ 4 root ...
2
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1answer
67 views

Is it possible to access any file or dir within a non-accessible directory? [duplicate]

Say I set my home /home/john directory as not readable for any other user. But I've forgotten to do so with some files within that directory, say ./.bashrc or ./Downloads/Presentation.ppt. Now, if ...
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7answers
6k views

My server is constantly being attacked [closed]

I am fairly new to the system administration world. I've been working on an application recently and when I check my application server logs, I constantly get various IP addresses trying to ssh into ...
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1answer
41 views

How to update all Debian packages from source code?

For building packages from source code, there is apt-get source --compile pkg-name. But for it to work, one has to run apt-get build-dep pkg-name beforehand, which downloads binary packages. Is it ...
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1answer
51 views

How can I test whether Chromium is running inside sandbox

I am using Chromium browser on Debian Wheezy. I read that Chromium is using sandbox to isolate its processes from the rest of the system and thus to increase security. How can I verify that Chromium ...
10
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2answers
211 views

A consistent and safe approach to passwordless accounts with SSH

I must admit that I like servers without passwords in some cases. A typical server is vulnerable to anyone who has physical access to it. So in some cases it is practical to lock it physically and ...
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0answers
18 views

Returning from a sleep the desktop displays shortly (before entering password), privacy issue

OS: Linux mint 17.1 Cinnamon 64-bit Cinnamon version 2.4.6 Intel Celeron: 900 @ 2.20Ghzx1 Memory 2 Gb Graphics Card: Intel Mobile 4 series integrated When I return to my computer after it has been ...
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2answers
84 views

How to prevent the messages about REMOTE HOST IDENTIFICATION HAS CHANGED

Is it possible to prevent the following message about: ( REMOTE HOST IDENTIFICATION HAS CHANGED ) When using only this connection syntax ssh xxx.xxx.xxx.xxx example of warning message: ssh ...
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1answer
90 views

How to force rpm and yum to fail if a GPG signature is missing or cannot otherwise be verified?

How can I force rpm and yum to fail if a GPG signature is missing from a package or otherwise cannot be verified due to a missing key? For the example below, assume the RPM has been signed but the key ...
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1answer
105 views

Reason why ssh RSA key would change?

Today I went to connect t my Centos 7 box via ssh and my sftp client and both indicated that the server RSA key finger print had changed. I've checked all my logs for suspicious activity but don't ...
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2answers
915 views

Ghost Vulnerability On Linux

It came to our notice that glibc needs to be upgraded from 2.2 to the latest version as per the release 5/6/7. My Question is that do I need to reboot the system, because we are having more then ...
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2answers
131 views

how to record all who that login to my linux machines and records them

I installed the package audit on my linux red-hat 6.x machine in order to view the recored of each user that log to my linux machine yum install audit kit installation from: ...
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1answer
116 views

GUFW or Firestarter in Fedora

Physician using Fedora 21 - I have very limited knowledge of Linux. I cannot make sense of iptables in Fedora. I used Debian before but moved away from Debian in great disgust after I realized their ...
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1answer
94 views

Can I update eglibc to a non-vulnerable version using Debian Squeeze 6 on x86_64 architecture?

I'm currently attempting to update eglibc on Debian Squeeze 6 on x86_64 architecture from version 2.11.3-4, which is vulnerable to the GHOST exploit, to version 2.11.3-4+deb6u4, which isn't vulnerable ...
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0answers
13 views

Finding out the script causing MySQL failed connections

I see lot of lines in mysql.log Connect Access denied for user 'M'@'localhost' (using password: NO) I am sure I don't have such a user on my system. I need to figure out what script is ...
4
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3answers
737 views

Any disk encryption that locks itself for some time after a number of failed attempts?

Is there any way to have your disk/partition/file encrypted (in Linux or as a hardware encryption; no Windows here) in such way that it locks itself for say 10 minutes after say 3 failed unlock ...
12
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1answer
6k views

Ghost Vulnerability - CVE-2015-0235

Does the Ghost Vulnerability require access (as in being a logged in user) to the effected OS in question? Can someone clarify the 'remote attacker that is able to make an application call'? I only ...
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1answer
454 views

GHOST: glibc gethostbyname buffer overflow

https://rhn.redhat.com/errata/RHSA-2015-0092.html I can see md5sums of the packages, but cannot download them and my package manager says I'm up-to-date. [root@notebook log]# grep glibc-2 yum.log | ...
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3answers
425 views

What are benefits and downsides of unprivileged containers?

The technical explanation of what is unprivileged container is quite good. However, it is not for ordinary PC user. Is there a simple answer when and why people should use unpriviliged containers, and ...
3
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2answers
34 views

How is the visibility of a file-system mount limited?

If a user mounts an encrypted file system, is it possible to limit the visibility of that file system such that other users are not able to view it or even see that the file system is mounted?
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1answer
62 views

unix system with malware

I have a CENTOS server that is infected with malware: top shows there's an unknown process that's consuming all the CPUs, if you kill it, it respawns with a different name. what's the best way to ...
0
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1answer
15 views

kernel security and IDS Firewall + AV together or not?

I try to hardening my server. For doing so, I got a general question: Should I install kernel security patches like selinux and an Anti-Virus with Intrusion Detection Firewall? Does it make sense to ...
5
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1answer
112 views

When running 'su - username', pam_group doesn't add additional groups from /etc/security/group.conf but sshd login does?

I am having trouble determining why su doesn't behave as the PAM configuration would imply. In short, using su to become another user should load secondary groups according to PAM configuration, but ...
6
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2answers
137 views

Run Ubuntu Security Updates every Saturday only

A clients wants to enable automatic security updates on their 12.04 box, but it has to be once per week, on saturday only. (Why I don't know) When I do dpkg-reconfigure -plow unattended-upgrades it's ...
2
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1answer
49 views

NIS and /etc/passwd

Shadow passwords are to be avoided in a NIS server, as suggested in this guide at paragraph 7.6. So: in a NIS server (a Unix or Unix-like system), should all the users be migrated to /etc/passwd from ...
22
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1answer
1k views

Can another program on X capture my root password while I type it in a virtual terminal?

Usually I only install open source programs on my linux box because I don't trust closed source applications. Recently I had to use Dropbox for a university project. I created a separate linux account ...
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1answer
13 views

How to restrict restrict remopte administration software to one domain name?

I currently have a server hosting a number of website on a debian server. I understand that all my domain names share the same IP so any of them will grant me access through SSH, but i was wondering ...
0
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1answer
86 views

How to run unattended-upgrades not daily but every few hours

By default unattended-upgrades runs with cron.daily, that is at most on a daily basis. This can be a lot of time for attackers. I'd like to run it every 4 hours, how can I do this?
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1answer
36 views

Finding out if my system is being used as a bot by looking at ifconfig?

Recently, I have often been suspicious that my router (a linux box) might have been used as a bot for spam blowout or something of that quality because I may have misconfigured my iptables rules by ...
2
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2answers
436 views

RHEL 7 (CentOS 7) security / ssh / sshd_config advise requested

I am not a sysadmin and try to create a more or less secure web server (LAMP based CentOS 7). I read several tutorials about setup an initial CentOS 7 droplet and got everything running fine. ...
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1answer
57 views

What considerations would I need when configuring iptables?

Synopsis I am looking at learning more about Server Administration. I have been running my own web server for a few years although many things were set-up by my friend and now I wish to learn more ...
0
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1answer
52 views

Sudo User: Not able to see the home directory of other users

I created sudo user hrsupport with following commands: hrsupport ALL=ALL, NOPASSWD: /bin/chown, /bin/chmod, /bin/chgrp, /scripts/pkgacct, /scripts/restorepkg How can I achieve this The hrsupport ...
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3answers
79 views

/etc/passwd permissions and GECOS field

The default permissions on Ubuntu (or even some BSD) distributions for the /etc/passwd file are 644. It is pointed out in questions like this that /etc/passwd is a sort of user database and it is ...
6
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2answers
79 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. ...
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0answers
25 views

How do I securely automate inputting passwords?

I would like to automate an SSH connection so that I wouldn't have to enter password and I am not allowed to use authorized_keys. I was thinking about making an expect script but I don't know where I ...