In a Nutshell
Linux is a free, open-source operating system made up of the Linux kernel, developed by Linus Torvalds, and the GNU toolkit, created by Richard Stallman. Together, they form what is commonly known as GNU/Linux. Linux is widely used in various fields but is typically deployed as a server OS. Because of this, Linux servers often run specific services and protocols, which can provide attackers with access vectors. Understanding these services, their functions, and potential vulnerabilities is crucial for penetration testers.
Types of Vulnerabilities
Privilege Escalation
Exploiting weaknesses to gain higher-level permissions than initially granted.
Weak File Permissions
Misconfigured permissions allow unauthorized users to access sensitive files.
Kernel Exploits
Flaws in the Linux kernel that allow attackers to execute malicious code at a system level.
Insecure SSH Configuration
Weak or default SSH settings that can be exploited for unauthorized remote access.
Unpatched Software
Outdated software with known vulnerabilities can be exploited if security patches are not applied.
Sudo Misconfigurations
Improperly configured sudo privileges allow non-admin users to execute commands as root.
Unrestricted Cron Jobs
Poorly managed cron jobs can allow attackers to execute malicious tasks automatically.
These vulnerabilities are not exhaustive.
Frequently Exploited Services
Apache Web Server
TCP Port 80/443
Hosts websites and serves web content over HTTP (80) or HTTPS (443)
SSH (Secure Shell)
TCP Port 22
Provides secure remote login and command execution
FTP (File Transfer Protocol)
TCP Port 21
Transfers files between client and server
SAMBA
TCP Port 445
Enables file and print services sharing over a network (mainly for Windows interoperability)
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