Cyber Security Deep Dive

Demystifying Web Security: Bugs, Vulnerabilities, and Top Exploits

Web applications are constantly targeted by malicious actors. Understanding common vulnerabilities and exploits is crucial for developers and security professionals to build and defend robust systems.

Common Web Vulnerabilities

These are some of the most prevalent flaws found in web applications that attackers actively exploit.

1. Cross-Site Scripting (XSS)

XSS allows attackers to inject malicious client-side scripts into web pages viewed by other users. This can lead to session hijacking, defacement, or redirection to malicious sites.

Example (Reflected XSS):

URL:
						https://example.com/search?query=<script>alert('XSS Attack!');</script>

Explanation: If the `query` parameter is not properly sanitized, the injected script will execute in the user's browser, displaying an alert.

2. XML External Entity (XXE) Injection

XXE vulnerabilities occur when an XML parser processes XML input containing references to external entities that are not properly secured. This can lead to local file inclusion (LFI), server-side request forgery (SSRF), or even remote code execution (RCE).

Example (LFI via XXE):

POST
						/api/xml_processor HTTP/1.1
						Content-Type: application/xml

						<?xml version="1.0"?>
						<!DOCTYPE foo [ <!ENTITY xxe SYSTEM "file:///etc/passwd"> ]>
						<data>&xxe;</data>

Explanation: The XML parser will attempt to read the `/etc/passwd` file and include its content in the response, potentially disclosing sensitive system information.

3. Server-Side Request Forgery (SSRF)

SSRF occurs when a web application fetches a remote resource without validating the user-supplied URL. An attacker can manipulate the application to make requests to internal network resources or other external systems.

Example (Accessing Internal API):

Request: GET
						/image?url=http://169.254.169.254/latest/meta-data/iam/security-credentials/

Explanation: If the application processes this URL, it might fetch sensitive AWS metadata from an EC2 instance, potentially exposing temporary credentials.

4. SQL Injection (SQLi)

SQLi allows an attacker to interfere with the queries that an application makes to its database. This can enable them to view data they are not normally able to retrieve, modify database data, or even execute administrative operations on the database.

Example (Bypassing Login):

Username: ' OR
						'1'='1 --
						Password: any_password

Explanation: The SQL query becomes `SELECT * FROM users WHERE username='' OR '1'='1' -- AND password='...'`, which always evaluates to true, bypassing authentication.

Top Exploits in the Wild (Illustrative Examples, not a comprehensive list of 30)

While a definitive "top 30" list changes frequently, these are examples of vulnerabilities that have seen widespread exploitation or high impact in recent years. Each usually has a CVE (Common Vulnerabilities and Exposures) identifier.

  • Log4Shell (CVE-2021-44228): A critical remote code execution (RCE) vulnerability in the Apache Log4j logging library.

    Impact: Allowed attackers to execute arbitrary code on vulnerable servers by simply logging a malicious string. Had a massive impact globally.

  • Microsoft Exchange Server Vulnerabilities (e.g., ProxyLogon - CVE-2021-26855): A chain of vulnerabilities allowing unauthenticated RCE on Microsoft Exchange servers.

    Impact: Enabled attackers to gain full control of Exchange servers, leading to widespread data breaches and ransomware attacks.

  • Zerologon (CVE-2020-1472): A critical elevation of privilege vulnerability in Microsoft's Netlogon Remote Protocol.

    Impact: Allowed attackers to compromise a Windows domain controller and gain full administrative control over the entire domain.

  • Atlassian Confluence RCE (CVE-2022-26134): An OGNL injection vulnerability in Atlassian Confluence Server and Data Center.

    Impact: Permitted unauthenticated remote code execution on vulnerable Confluence instances.

  • Spring4Shell (CVE-2022-22965): A remote code execution vulnerability affecting Spring Framework.

    Impact: Allowed attackers to gain RCE on applications running certain versions of the Spring Framework, particularly on specific configurations.

  • MOVEit Transfer SQL Injection (CVE-2023-34362): Multiple SQL injection vulnerabilities in the MOVEit Transfer web application.

    Impact: Led to widespread data theft from organizations using the affected file transfer software.

  • Citrix NetScaler / ADC Vulnerabilities (e.g., CVE-2019-19781): Various vulnerabilities, including directory traversal and remote code execution.

    Impact: Allowed unauthenticated attackers to execute arbitrary code, leading to network compromise.

  • VMware vCenter Server Vulnerabilities (e.g., CVE-2021-21972): Multiple vulnerabilities in the vSphere Client plugin.

    Impact: Allowed attackers to execute arbitrary code on the underlying vCenter server, potentially gaining control over the entire virtualized infrastructure.

  • Fortinet FortiOS SSL VPN Vulnerabilities (e.g., CVE-2018-13379): Path traversal vulnerability allowing access to system files.

    Impact: Allowed attackers to download sensitive files, including session files containing user credentials, from vulnerable FortiOS devices.