Questions tagged [security]
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.
294
questions
211
votes
3answers
20k views
Security implications of forgetting to quote a variable in bash/POSIX shells
If you've been following unix.stackexchange.com for a while, you
should hopefully know by now that leaving a variable
unquoted in list context (as in echo $var) in Bourne/POSIX
shells (zsh being the ...
192
votes
8answers
145k views
Allow setuid on shell scripts
The setuid permission bit tells Linux to run a program with the effective user id of the owner instead of the executor:
> cat setuid-test.c
#include <stdio.h>
#include <unistd.h>
int ...
89
votes
3answers
30k views
Why is there a big delay after entering a wrong password?
I notice a weird (well, according to me) thing about passwords. For example, if I type an incorrect password during login, there will be a few seconds' delay before the system tells me so. When I try ...
122
votes
2answers
20k views
When was the shellshock (CVE-2014-6271/7169) bug introduced, and what is the patch that fully fixes it?
Some context about the bug: CVE-2014-6271
Bash supports exporting not just shell variables, but also shell
functions to other bash instances, via the process environment to
(indirect) child ...
121
votes
8answers
28k views
Which is the safest way to get root privileges: sudo, su or login?
I would like to have the root account in safety even if my unprivileged user is compromised.
On Ubuntu you can only use sudo for "security reasons" by default. However I am not sure it is any safer ...
90
votes
3answers
421k views
SSH login with clear text password as a parameter? [duplicate]
I need to login to a user that I've created on a remote host running Ubuntu. I can't use an ssh key because the ssh login will happen from a bash script ran within a server that I won't have access to ...
173
votes
8answers
211k views
What's the difference between /sbin/nologin and /bin/false
Technically, unless pam is set up to check your shell with pam_shells neither of these can actually prevent your login, if you're not on the shell. On my system they are even different sizes, so I ...
85
votes
10answers
225k views
How to create SHA512 password hashes on command line
In Linux I can create a SHA1 password hash using sha1pass mypassword. Is there a similar command line tool which lets me create sha512 hashes? Same question for Bcrypt and PBKDF2.
142
votes
9answers
18k views
The myths about malware in Unix / Linux
Is it possible for my Linux box to become infected with a malware?
I haven't heard of it happening to anyone I know, and I've heard quite a few times that it isn't possible. Is that true?
If so, ...
35
votes
7answers
42k views
Can root/superuser read my read-protected files?
On shared unix hosting, if I have a file sensitive-data.txt and I issue:
chmod 600 sensitive-data.txt
Can root user still read my file? Specifically I'm wondering if it's safe to store my password ...
27
votes
2answers
2k views
Security implications of running perl -ne '…' *
Apparently, running:
perl -n -e 'some perl code' *
Or
find . ... -exec perl -n -e '...' {} +
(same with -p instead of -n)
Or
perl -e 'some code using <>' *
often found in one-liners ...
8
votes
2answers
4k 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.
...
68
votes
4answers
12k views
Is there any way to keep a command from being added to your history?
Is there any way to keep a command from being added to your history? I have a command that I want to keep out of my history file, and I really don't care to have it there when I search the history ...
70
votes
3answers
6k views
How does curl protect a password from appearing in ps output?
I noticed some time ago that usernames and passwords given to curl as command line arguments don't appear in ps output (although of course they may appear in your bash history).
They likewise don't ...
16
votes
10answers
2k views
Concern about logging in as root overrated?
For personal linux on my personal notebooks, I've usually set my environment to autologin as root even under X or lower runlevels. I've found my workflow is very pleasant and fast, without any ...
12
votes
1answer
2k views
Log every invocation of every SUID program?
I would like to have a log file that contains an entry for every time a user runs any suid program, containing the user name, the program and any command line arguments passed to it. Is there a ...
6
votes
1answer
2k views
What should I check after an unauthorized access?
I accidentally left an open port on my router, leaving access to one of my computers via SSH, using a rather insecure password. I noticed because I checked /var/log/auth.log and there is just one ...
89
votes
5answers
39k views
Why is root login via SSH so bad that everyone advises to disable it?
Everybody on the Internet advises to disable root login via SSH as it is a bad practice and a security hole in the system, but nobody explains why it is so.
What is so dangerous in enabling root ...
24
votes
2answers
40k views
How can you log every command typed
How can you log every command someone has entered into the shell?
I'm asking on both the basis of protecting yourself if you are logged into someone else's server and something breaks, or if someone ...
48
votes
7answers
79k 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 ...
14
votes
2answers
670 views
How can I be sure that a directory or file is actually deleted?
I know that most files, when deleted, aren't actually removed from the disk, and can be recovered later.
How can I ensure that a directory I had deleted will actually be removed from the disk? Are ...
17
votes
1answer
540 views
Security Implications of using unsanitized data in Shell Arithmetic evaluation
In a comment to a recent question, Stéphane Chazelas
mentions that there are security implications to double parentheses arithmetic such as:
x=$((1-$x))
on most shells.
My Google skills seem to be ...
20
votes
3answers
7k views
Myth or reality: SELinux can confine the root user?
I read or heard somewhere (maybe in LinuxCBT's SELinux course; but I'm not sure) that there are online Linux servers, for which the password of the root user is also given. The Linux server is ...
8
votes
1answer
750 views
How is the authenticity of Debian packages guaranteed?
What security systems and processes are in place to prevent malicious third parties from hacking/compromising the security of code in the Debian mirrors, or to verify that the packages we get are in ...
4
votes
1answer
3k views
Is there a way to get security updates for wheezy after EOL
I know the best solution would be to upgrade the server after Debian wheezy has reached End Of LIfe in May 2018, but is there a way to continue running an old wheezy instance and get some minimal ...
9
votes
3answers
3k views
Securely feeding a program with a password
After understanding the problem with using a password in the command line, I need to find a way of feeding a program with a password without it being a problem (without the password being recorded ...
79
votes
8answers
73k views
Does /usr/sbin/nologin as a login shell serve a security purpose?
In my /etc/passwd file, I can see that the www-data user used by Apache, as well as all sorts of system users, have either /usr/sbin/nologin or /bin/false as their login shell. For example, here is a ...
93
votes
3answers
20k views
How do I recover from the Heartbleed bug in OpenSSL?
CVE-2014-0160 a.k.a. Heartbleed is a vulnerability in OpenSSL. It looks scary.
How do I determine whether I am affected?
If I'm affected, what do I need to do? Apparently upgrading isn't enough.
asked Apr 8 '14 at 10:42
Gilles 'SO- stop being evil'
594k143 gold badges1216 silver badges1732 bronze badges
66
votes
18answers
16k views
Root access that can't change root password?
We are having a little problem on a server. We want that some users should be able to do e.g. sudo and become root, but with the restriction that the user can't change root password. That is, a ...
29
votes
12answers
12k views
Erasing a Linux laptop
I have a laptop with Debian on it, and I am going to sell this laptop.
Would it suffice to erase the Debian installation before selling it to completely clean up my laptop from my personal data, and ...
27
votes
5answers
37k views
Block Particular Command in Linux for Specific user
How to block command, let say mkdir for specific user ?
What I did just created read-only function and store in users profile ~/.bashrc
/bin/mkdir() {
echo "mkdir command not allow for you"
...
19
votes
1answer
10k 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 ...
10
votes
1answer
13k views
How to get Oracle java 7 to work with setcap cap_net_bind_service+ep
I am trying to grant the java executable the right to open ports below 1024 on Linux. Here is the setup
/home/test/java contains the Oracle Server JRE 7.0.25
CentOS 6.4
Here is what getcap returns
...
12
votes
4answers
32k 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 :
...
8
votes
2answers
3k views
change /proc/PID/environ after process start
$ k=v p &
[1] 3028
is there any way for p to change the contents of /proc/3028/environ to not mention k=v while p is still running?
9
votes
1answer
11k views
How to enable user_namespaces in the kernel? (For unprivileged `unshare`.)
My Linux kernel must have been configured with user_namespaces when built, but their use is restricted after boot and has to be explicitly enabled. Which sysctl should I use?
(If this was turned on, ...
asked Aug 13 '16 at 16:37
imz -- Ivan Zakharyaschev
12.1k10 gold badges45 silver badges99 bronze badges
13
votes
1answer
4k 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 ...
45
votes
5answers
43k views
Why there is no https transport for debian apt tool?
With all paranoia that has come with NSA revelations and everything, I'm wondering why debian package installation mechanism does not support HTTPS for its transport, let alone using it by default.
I ...
38
votes
1answer
7k views
How to create a darknet/Tor web site in Linux?
I have heard a lot about creating darknet sites lately. I also use the Tor browser frequently.
The tor service is running in my Debian server at home, and it was installed with:
sudo apt-get ...
49
votes
2answers
58k views
How to identify a process which has no pid?
I have a process which listen to 2 ports : 45136/tcp and 37208/udp (actually I assume it is the same process). But netstat doesn't return any pid :
netstat -antlp | grep 45136
tcp 0 0 0.0....
49
votes
3answers
187k views
Convert Amazon .pem key to Putty .ppk key Linux
I have generated and downloaded a private .pem key from AWS. However, to use Putty in order to connect to the virtual machine, I must have that key in .ppk format. The process of conversion is ...
23
votes
8answers
81k views
Hiding Password in Shell Scripts
How can I hide a password in shell scripts? There are a number of scripts that are accessing database. If we open the script others also aware the username and password. So if anyone knows how to hide ...
27
votes
3answers
11k 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 tty=...
20
votes
2answers
8k views
What to use to harden Linux box? Apparmor, SELinux, grsecurity, SMACK, chroot?
I am planning to go back to Linux as a Desktop machine.
I would like to make it more secure. And try a few hardening techniques, especially since I plan to get my own server.
What would be a good, ...
16
votes
5answers
2k views
Monitoring activity on my computer.
So recently I found that someone has been using my computer without consent, browsing folders, etc....
I could change all my passwords straight away, but I'm curious as the what the intruding party ...
44
votes
3answers
25k views
How can I determine if someone's SSH key contains an empty passphrase?
Some of my Linux & FreeBSD systems have dozens of users. Staff will use these "ssh gateway" nodes to SSH into other internal servers.
We're concerned that some of these people use an unencrypted ...
12
votes
7answers
49k views
vsftpd fails pam authentication
Moving a tried-and-true vsftpd configuration onto a new server with Fedora 16, I ran into a problem. All seems to go as it should, but user authentication fails. I cannot find any entry in any log ...
14
votes
2answers
1k views
What are the security issues and race conditions in using `find -exec`?
From the find man page:
-exec command ;
There are unavoidable security problems
surrounding use of the -exec action; you should use the
-execdir option instead.
-execdir command {} +
...
13
votes
8answers
5k views
How to prevent a process from writing files
I want to run a command on Linux in a way that it cannot create or open any files to write. It should still be able to read files as normal (so an empty chroot is not an option), and still be able to ...
10
votes
1answer
2k views
How does the kernel prevent a malicious program from reading all of physical RAM?
If I write a program that tries to read memory at every possible address, and I run it on a "full" Unix, it will not be able to access all of the physical RAM. But how does the operating system ...
