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Linux threat Hunting

Apr 01, 2024, 3 min read

MOCs

Hunting Techniques

Looking at /etc/passwd

If use has /bin/bash then has access to the bash shell if user has /no/login the user can’t log in. Example /etc/passwd. When the /etc/passwd is made the higher

root:x:0:0::/root:/bin/bash
nobody:x:65534:65534:Kernel Overflow User:/:/usr/bin/nologin
dbus:x:81:81:System Message Bus:/:/usr/bin/nologin
bin:x:1:1::/:/usr/bin/nologin
daemon:x:2:2::/:/usr/bin/nologin
mail:x:8:12::/var/spool/mail:/usr/bin/nologin
ftp:x:14:11::/srv/ftp:/usr/bin/nologin
http:x:33:33::/srv/http:/usr/bin/nologin

Decoding /etc/passwd

username:x:userid:userid info:groupid:homedir:shell

root:x:0:0::/root:/bin/bash

Bash

To hide a bash command change .bashrc to set history size to 0 or put a space ’ ’ in front of your command.

The hardlink is the number after the permissions for the directory as you can see below we have 3 hardlinks. Hardlinks are like softlinks to some degree but when root the .. will show how many directories are in the next directory up.

drwxr-xr-x 3 root root 4096 Mar 6 09:35 ..

Debugfs

Can get the filesystem from using the command mount

Usage: sudo debugfs <filesystem>

Then you can move around and cd into directories as normal ls / and cd /home this can show files that are hidden from your normal terminal.

Processes Tree

The command pstree will get you a tree of processes running:

systemd─┬─ModemManager───3*[{ModemManager}]
        ├─NetworkManager───3*[{NetworkManager}]
        ├─accounts-daemon───3*[{accounts-daemon}]
        ├─avahi-daemon───avahi-daemon
        ├─blueman-tray───3*[{blueman-tray}]
        ├─bluetoothd
        ├─chrome_crashpad───2*[{chrome_crashpad}]
        ├─colord───3*[{colord}]
        ├─crond
        ├─cupsd
        ├─dbus-broker-lau───dbus-broker
        ├─firefox─┬─Isolated Servic───30*[{Isolated Servic}]
        │         ├─Isolated Servic───28*[{Isolated Servic}]
        │         ├─Isolated Servic───27*[{Isolated Servic}]
        │         ├─19*[Isolated Web Co───25*[{Isolated Web Co}]]
        │         ├─Isolated Web Co───32*[{Isolated Web Co}]
        │         ├─6*[Isolated Web Co───26*[{Isolated Web Co}]]
        │         ├─Isolated Web Co───31*[{Isolated Web Co}]
        │         ├─2*[Isolated Web Co───30*[{Isolated Web Co}]]
        │         ├─Isolated Web Co───27*[{Isolated Web Co}]
        │         ├─Privileged Cont───26*[{Privileged Cont}]
        │         ├─RDD Process───3*[{RDD Process}]
        │         ├─Socket Process───4*[{Socket Process}]
        │         ├─Utility Process───3*[{Utility Process}]
        │         ├─3*[Web Content───20*[{Web Content}]]
        │         ├─WebExtensions───27*[{WebExtensions}]
        │         └─229*[{firefox}]
        ├─geoclue───3*[{geoclue}]

Network Monitoring

Either user ss -tunap or netstat -plunt

Find Where Process is Running

Ways to Find Process

pwdx

pwdx <pid>

lsof

lsof -p <pid> | grep cwd

/proc

Get location of where process is running readlink -e /proc/<pid>/cwd
Get the executable the process is running cat /proc/<pid>/cmdline

In /proc you can locate all process’ running. The files are named the same as the PID of the process running. In those sub directories they contain information about the process that is running.

Finding Hidden Process

use the command unhide checkproc

Searching Files

Search Files based on Time

After Date

Example:
find <dir> -type f -newerct <date> | less
Usage:
find /proc -type f -newerct 2023-03-21 | less

Search Between Dates

Example:
find <dir> -type f -newerct <date-from> ! -newerct <date-t0> | less
Usage:
find /proc -type f -newerct 2023-03-21 ! -newerct 2023-04-21 | less

Newer Than Other File

Example:
find <dir> -type f -newer <file> | less
Usage:
find /etc/ -type f -newer /etc/filename | less

Who Is Logged In

last

w

lastlog

sudo cat /var/log/auth.log

Graph View

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