Understanding Web Security: Key Vulnerabilities and Penetration Testing Methods

What Is Web Security

Web security encompasses all risks that arise when users access server resources through browsers or other clients; the entire request‑response process can be targeted. A typical web application consists of a client, web server, application server, and database—essentially the front‑end and back‑end components.

Penetration Testing Classification

Penetration testing (or pen‑test) simulates hacker behavior under authorized conditions to discover security weaknesses through information gathering, vulnerability exploitation, and privilege escalation, ultimately producing a risk report. Common tools include AppScan, AWVS, Nessus, Burp Suite, sqlmap, various scripts, sub‑domain scanners, Nmap, and SlowHTTPTest.

Common Web Vulnerabilities

SQL Injection occurs when user input is not properly validated, allowing an attacker to append malicious SQL statements to legitimate queries, leading to unauthorized data access or command execution.

Cross‑Site Scripting (XSS) involves injecting malicious script code into web pages; when browsers render the page, the script executes, enabling theft of cookies, session hijacking, or other attacks. Improper handling of characters such as < and > often causes XSS.

File Upload exploits insufficient validation of uploaded files. Attackers can upload a web shell (e.g., <?php @eval($_POST['cmd']); ?>) and execute arbitrary commands if the server parses the file as executable. Successful exploitation requires the target to accept uploads, store them in a web‑accessible location, and allow execution.

Deserialization abuses the process of converting serialized data back into objects. By crafting malicious serialized Java objects that override readObject, attackers trigger arbitrary code execution via Java reflection (e.g., Runtime.getRuntime().exec()).

Vulnerability Combination (Upgrade)

Attackers often chain multiple flaws to increase impact, such as:

SQL Injection + XSS

CSRF + XSS

File Upload + XSS

File Upload + File Inclusion

File Upload + Decompression

…and other permutations.