Expression language injection

Expression Language Injection

Expression Language Injection is a cybersecurity attack that targets web applications utilizing Expression Language (EL), a scripting language used for embedding dynamic content within web pages. By exploiting vulnerabilities in the EL interpreter, attackers can inject malicious code to execute arbitrary commands or gain unauthorized access to sensitive data.

How Expression Language Injection Works

1. Identification: Attackers first identify web applications that rely on expression language to generate dynamic web content.

2. Code Injection: Malicious code is then injected into the input fields or parameters of the targeted web application. This can be done through various means such as user input forms, HTTP request parameters, or cookies.

3. Exploitation: The injected code may contain directives or expressions that reference system variables, file access commands, or other system-level operations. When the web server processes the injected expression language, it interprets and evaluates the code, leading to the execution of the attacker's commands.

4. Unauthorized Access: Depending on the nature of the injected code, the attacker can potentially gain unauthorized access to sensitive data, manipulate the application's behavior, or even compromise the entire system.

Prevention Tips

To mitigate the risk of Expression Language Injection attacks, consider implementing the following preventive measures:

1. Input Validation: Apply strict input validation and sanitization techniques to user inputs. This prevents the execution of arbitrary commands and ensures that only valid, expected input is processed by the application.

2. Secure Configuration: Configure the web application server to enforce security measures such as restricting access to system resources. This helps limit the attack surface and prevents unauthorized access to sensitive files or functionality.

3. Least Privilege Principle: Follow the principle of least privilege by granting the web application permissions and access rights only to the necessary resources. By minimizing the privileges granted to the application, the potential impact of a successful attack can be greatly reduced.

Examples

Example 1: Accessing System Information

java ${'Operating System: ' + java.lang.System.getProperty('os.name') }

In this example, the attacker injects an expression that retrieves the operating system name using the java.lang.System.getProperty function. By executing this injection, the attacker can gather sensitive system information.

Example 2: File Access

java ${ T(java.lang.Runtime).getRuntime().exec('cat /etc/passwd') }

This example demonstrates a code injection that attempts to execute the cat /etc/passwd command, which displays the contents of the password file on Unix-like systems. If successful, the attacker can gain access to sensitive user information stored in the file.

Related Terms

• Cross-Site Scripting (XSS): Another type of web application attack where malicious scripts are injected into web pages viewed by other users.
• SQL Injection: An attack that exploits vulnerabilities in web applications to execute unauthorized SQL commands.
• Code Injection: The general concept of injecting malicious code into an application to alter its behavior or gain unauthorized access.

Note: The prevention tips and examples provided serve as general guidelines to enhance understanding of Expression Language Injection. Implementing these measures alone may not guarantee protection against all possible variations of this attack. Regular security testing, monitoring, and staying informed about the latest security practices are crucial for maintaining the security of web applications.