Author: Alok

DevSecOps

Strings command in linux

strings /lib64/libc.so.6 |grep GLIBC

strings /bin/ls


Usage: strings [option(s)] [file(s)]
 Display printable strings in [file(s)] (stdin by default)
 The options are:
  -a - --all                Scan the entire file, not just the data section [default]
  -d --data                 Only scan the data sections in the file
  -f --print-file-name      Print the name of the file before each string
  -n --bytes=[number]       Locate & print any NUL-terminated sequence of at
  -<number>                   least [number] characters (default 4).
  -t --radix={o,d,x}        Print the location of the string in base 8, 10 or 16
  -w --include-all-whitespace Include all whitespace as valid string characters
  -o                        An alias for --radix=o
  -T --target=<BFDNAME>     Specify the binary file format
  -e --encoding={s,S,b,l,B,L} Select character size and endianness:
                            s = 7-bit, S = 8-bit, {b,l} = 16-bit, {B,L} = 32-bit
  -s --output-separator=<string> String used to separate strings in output.
  @<file>                   Read options from <file>
  -h --help                 Display this information
  -v -V --version           Print the program's version number
strings: supported targets: elf64-x86-64 elf32-i386 elf32-iamcu elf32-x86-64 a.out-i386-linux pei-i386 pei-x86-64 elf64-l1om elf64-k1om elf64-little elf64-big elf32-little elf32-big pe-x86-64 pe-bigobj-x86-64 pe-i386 plugin srec symbolsrec verilog tekhex binary ihex

connect to wifi using terminal in ubuntu

1.Create file and add wifi name and creds (vi /etc/wpa_supplicant.conf)

network={
    ssid="ssid_name"
    psk="password"
}

2.Connect

sudo wpa_supplicant -B -i wlan0 -c /etc/wpa_supplicant.conf -D wext
sudo dhclient wlan0

More : https://askubuntu.com/questions/138472/how-do-i-connect-to-a-wpa-wifi-network-using-the-command-line

https://askubuntu.com/questions/294257/connect-to-wifi-network-through-ubuntu-terminal

sftp setup to restrict user to some /path

WHY?
– Secure access
– Secure path

adduser kool -s /sbin/nologin

#edit /etc/ssh/sshd_config and ADD

Subsystem sftp internal-sftp
   Match User kool
   ChrootDirectory /opt/dir1/dir2
   ForceCommand internal-sftp
   X11Forwarding no
   AllowTcpForwarding no


chown root:root -R /opt/dir1/dir2
chmod 755 -R /opt/dir1/dir2

chown kool:kool /opt/dir1/dir2/kool
chmod 700 /opt/dir1/dir2/kool

install openvas in centos8

sed -i 's/enforcing/disabled/g' /etc/selinux/config

reboot

dnf update

yum config-manager --set-enabled PowerTools
yum install epel-release

wget -q -O - http://www.atomicorp.com/installers/atomic |sh

yum install openvas

openvas-setup

More : https://github.com/Atomicorp/gvm

  • Cronjob to update CVE database
10 1 * * * /usr/sbin/greenbone-nvt-sync > /dev/null
10 2 * * * /usr/sbin/greenbone-scapdata-sync > /dev/null
10 3 * * * /usr/sbin/greenbone-certdata-sync > /dev/null

Openvas API:


gvm-cli --gmp-username USRENAME --gmp-password PASSWORD socket --sockpath /var/run/gvm/gvmd.sock --xml "<get_tasks/>"

gvm-cli socket --sockpath /var/run/gvm/gvmd.sock --xml "<get_version/>"

iptables port allow/block

//Block port 8080

iptables  -A INPUT -p tcp --dport 8080 -j DROP

//Allow port 8080

iptables -A INPUT -p tcp -m tcp --dport 8080 -j ACCEPT

//Delete rule from same command(-D)

iptables  -D INPUT -p tcp --dport 8080 -j DROP

//Delete iptable rule for 8080 as per line number

iptables -L --line-numbers
iptables -D INPUT 1

//List rules

iptables -S
iptables -S TCP
iptables -L INPUT
iptables -L INPUT -v

#save
service iptables save

Pod affinity, readiness, liveness in kubernetes

why:

pod affinity: Attracts pods with with matching label.
readiness : checks pod health before sending any traffic
liveness : checks health of pod

kubectl get nodes --show-labels

kubectl label nodes <node-name> <label-key>=<label-value>

kubectl label nodes lp-knode-02 disk=ssd
kubectl label nodes lp-knode-02 nodename=lp-knode-02
apiVersion: apps/v1
kind: Deployment
metadata:
  name: httpd-affinity-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: httpd-affinity
  template:
    metadata:
      name: httpd-affinity-deployment
      labels:
        app: httpd-affinity
        env: prod
    spec:
      affinity:
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
            - matchExpressions:
              - key: disk
                operator: In
                values:
                - ssd
      containers:        
      - name: httpd-node-affinity
        image: httpd
        imagePullPolicy: IfNotPresent
        resources:
          requests:
            memory: "256Mi"
            cpu: "100m"
          limits:
            memory: "256Mi"
            cpu: "100m"
        ports:
        - name: httpd-port
          containerPort: 80
        livenessProbe:
          httpGet:
            path: /index.html
            port: 80
            httpHeaders:
            - name: Custom-Header
              value: custom1
          initialDelaySeconds: 10
          periodSeconds: 10
          timeoutSeconds: 5
          failureThreshold: 3
        readinessProbe:
          exec:
            command:
            - cat
            - /usr/local/apache2/htdocs/index.html
          initialDelaySeconds: 10
          periodSeconds: 10

More :
https://kubernetes.io/docs/concepts/scheduling-eviction/assign-pod-node/
https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/

Special File Permissions in linux setuid, setgid, sticky bit

setuid permission:

When program is executed with setuid permission it will executed as owner of that program.

-rwsr-xr-x. 1 root root 27856 Aug  9  2019 /usr/bin/passwd

as passwd has setuid set that’s why normal user can reset their password

#exec will be as owner user
chmod u+s  file_name 

#exec will be as owner user
chmod 4750   file_name

setgid permission:

When program is executed with setgid permission it will executed as group owner of that program.

-r-xr-sr-x. 1 root tty 15344 Jun 10  2014 /usr/bin/wall

as wall has setgid enabled it has all the permission as group tty has.

chmod u+g  file_name 
chmod 2700   file_name

Sticky bit:

Owner of files and directory and root can only delete the file when sticky bit is set.

drwxrwxrwt.  16 root root 4096 Oct 10 10:10 tmp

all linux /tmp directory has sticky bit enabled.

chmod +t /tmp

NOTE: Capital S,T displayed when user does not have execute permission on that file