How to Perform a Vulnerability Check on Ubuntu 18.04 Using Bash Shell Script

Discover how to create an effective bash script to check for vulnerabilities in Ubuntu 18.04 and learn key troubleshooting tips to enhance your security measures.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: vulnerability check on Ubuntu 18.04 Bash Shell Script

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Perform a Vulnerability Check on Ubuntu 18.04 Using Bash Shell Script

In the realm of system security, conducting regular vulnerability checks is paramount, especially on popular systems like Ubuntu 18.04. While it’s easy to feel intimidated by the prospect of writing scripts, a simple bash script can efficiently help identify potential vulnerabilities associated with password management. In this guide, we'll explore the problem of checking for encrypted passwords in the /etc/passwd file using a bash script and how to correct common pitfalls that might arise.

The Problem: Understanding the Vulnerability Check

Many applications need to confirm that user passwords are stored securely. In Ubuntu, one typical method is to check whether the corresponding data in /etc/passwd is encrypted. For instance, if a user account displays a password that isn't represented as x, it indicates that the password is not encrypted and thus vulnerable.

Here's what the script was originally trying to achieve:

Check for the existence of /etc/shadow: This file stores encrypted user passwords, making its absence a red flag.

Read through the /etc/passwd file: Identify any user entries with plaintext passwords.

However, the initial code presented had some flaws that prevented it from functioning as intended.

The Script Breakdown

Let's begin with the initial script:

[[See Video to Reveal this Text or Code Snippet]]

Key Issues Identified

Using a Subshell: The main issue lies with the line cat /etc/passwd | while read. Piping into while spawns a subshell, and as a consequence, the vuln variable defined outside can’t be altered within the subshell.

Inefficient Comparison Operators: The comparison [ $vuln == 1 ] uses an operator that’s not compatible in all shell contexts; = is safer for POSIX compliance.

The Solution: Fixing the Script

Efficient Variable Management

To resolve the issue with the subshell, you can modify the code to avoid using pipes:

[[See Video to Reveal this Text or Code Snippet]]

This change ensures the while loop reads directly from /etc/passwd without entering a subshell.

Simplifying with grep

Additionally, an even simpler solution, without needing full script mechanics, is to use the grep command:

[[See Video to Reveal this Text or Code Snippet]]

This command checks if any line in /etc/passwd has a plaintext password and promptly evaluates the system's vulnerability status.

Conclusion

In summary:

When scripting for security checks in Ubuntu, it's crucial to ensure that your variables are properly managed to yield accurate results.

Utilizing commands like grep can vastly simplify the process and make scripts more efficient.

By following these guidelines and practicing with your bash scripts, you can bolster the security posture of your Ubuntu systems effectively. Stay safe and secure, and happy scripting!