Cyber Security: Detect and remove trojans in a Linux operating system

Jika kerentanan terdeteksi di sistem operasi Linux Anda tetapi Anda tidak mengambil tindakan pencegahan, trojan dapat dimasukkan ke dalam sistem Anda. Anda harus menghapus trojan dari sistem Anda sesegera mungkin. Selain itu, Anda harus memperkuat keamanan sistem Anda dengan menggunakan beberapa metode. Misalnya, Anda dapat menginstal patch keamanan, mengontrol izin sistem, mengaudit operasi, dan menganalisis log.

Step 1: Use Security Center to detect trojan

Masuk ke Security Center console untuk menangani peringatan dan menghapus trojan yang terdeteksi sesegera mungkin. Untuk informasi selengkapnya, lihat Melihat dan menangani peristiwa peringatan.

Perbaiki kerentanan sedini mungkin untuk memperkuat keamanan sistem Anda. Untuk informasi selengkapnya, lihat Melihat dan menangani kerentanan perangkat lunak Linux.

Step 2: Query attack details

Run the last and lastlog commands to query the last logon time and the logon account. Then, lock abnormal accounts.

Run the grep -i Accepted /var/log/secure command to query the IP addresses that are used to log on to your system from a remote location.

Run the following commands to query cron jobs:

/var/spool/cron/ /etc/cron.hourly /etc/crontab Run the find / -ctime 1 command to query the last update time of a file. This way, you can identify trojan files.

Check the /etc/passwd and /etc/shadow files for malicious users.

Check the /tmp, /vat/tmp, and /dev/shm temporary directories. The permission of these directories is 1777. Therefore, these directories can be used to upload trojan files.

Check whether exceptions exist in the logs of services such as Tomcat and NGINX, whose service ports are accessible from the Internet.

Run the service --status-all | grep running command to check whether exceptions exist in the services that are running.

Run the chkconfig --list | grep :on command to check whether exceptions exist in the services that automatically start.

Run the ls -lt /etc/init.d/ | head command to check whether abnormal startup scripts exist.

Step 3: Run commonly used commands to detect trojans

Command

Description

ps or top

You can run these commands to query the running processes and system resources that are occupied by these processes. This way, you can identify abnormal processes.

pstree

You can run this command to visualize the relationship among processes in a treemap.

lsof

You can run this command to query the files opened by a process, the files or directories occupied by a process, the process that opens a specific port, and all the open ports in the system.

netstat

You can run this command to query all the ports monitored by the system, network connection status, and the IP addresses from which excessive connections are established.

iftop

You can run this command to monitor the network traffic forwarded over TCP connections in real time. This way, you can distinguish between and sort inbound and outbound traffic, and identify the IP addresses that have abnormal network traffic.

nethogs

You can run this command to monitor the network traffic generated by each process and sort the processes by traffic volume in descending order. This way, you can identify abnormal processes with unusual large traffic.

strace

You can run this command to trace system calls executed by a specific process. This way, you can analyze the running status of trojans.

strings

You can run this command to obtain the strings of printable characters in files. Then, you can use the strings to analyze trojans.