Most Common Vulnerabilities in Java and How to Fix

In today's world, Java supports a wide variety of applications, from commercial applications to Android apps and systems that process massive amounts of data. Among computer languages, Java ranks high in popularity. Developers all across the globe love it because of its solid performance, rich library support, and platform freedom.

Nevertheless, security flaws in Java are common because of the language's popularity. Data breaches, financial losses, and reputational harm can result from software vulnerabilities, which get worse by advanced levels of cyberattacks.

Ensuring the security of your Java application is an essential part of developing responsible software and a technical need. Here we will go over some of the most prevalent security holes in Java apps, how they occur, the damage they can do, and most importantly, how to fix them.

Common Vulnerabilities in Java

1. XML External Entity Attacks

When malicious actors gain access to your server's XML parser, they are committing XML external entity attacks (XXE). Further confidential data, such as AWS credentials, may be retrieved by attackers using an XXE, in addition to user information and configuration files.

Since the majority of Java XML parsers allow the prerequisites for XXE by default, Java applications are especially vulnerable to XXE.

2. Insecure Deserialization

Programming objects, such as Java objects, undergo a process called serialisation to transform them into a format suitable for storage in a database or transmission over a network. If an object has been serialised, deserialization is the process of reading it from a file or the network and converting it back into an object. Object serialisation and deserialization are features of many programming languages. Ruby, Python, PHP, and Java are just some examples.

When an attacker is able to modify the serialised object in a way that causes unexpected effects in the program's flow, this vulnerability is known as insecure deserialization. Authentication bypass, denial of service, or even arbitrary code execution are common outcomes of unsecured deserialization issues, making them an often severe vulnerability.

Keep a watch out for patches and ensure that dependencies are up to date in order to avoid insecure deserialization. Verify that any third-party code you use is secure; insecure deserialization issues are sometimes introduced via dependencies. Using plain old texts and arrays instead of serialised objects is a good approach.

3. Remote Code Execution

When malicious actors are able to remotely execute their own code on your computer, this is known as a remote code execution vulnerability (RCE). Command injection vulnerabilities are one potential entry point for this. They occur when user input is directly appended to a system command and is a form of remote code execution. The program treats the user's input as code since it cannot tell the difference between user input and system commands. The hacker can take control of the computer and run any program they choose. Implementing strong input validation with an allowlist is one of the simplest approaches to avoid command injection.

4. Command Injection

Another kind of injection issue is command injection. An application is prone to injection when it fails to adequately differentiate between trusted user data and code. Injecting malicious code into system OS commands is known as command injection. There are additional ways in which injection vulnerabilities can appear.

The SQL Injection Attack
To understand the point, consider a SQL injection attack, where the perpetrator inserts data in order to alter SQL commands. Attackers can execute arbitrary SQL code when the program fails to properly validate user input. This happens when the SQL language is manipulated by inserting special characters.

By manipulating the format of your application's SQL queries, an attacker can steal data, alter data, or even execute arbitrary commands in the underlying operating system. This vulnerability is known as SQL injection. Parameterised statements are the most effective defence against SQL injections since they make the injection almost impossible to execute.

NoSQL Injection
You won't always see SQL in databases. A database that does not employ the SQL language is called a NoSQL database. Attacks that insert data into the logic of these database languages are known as NoSQL injections. When it comes to the potential for authentication bypass and remote code execution, NoSQL injections are on par with SQL injections.

Injection attacks can affect any cutting-edge NoSQL database, including MongoDB, Couchbase, Cassandra, and HBase. NoSQL queries are usually composed in the application's programming language and have a database-specific syntax. This is likewise the case with database-specific approaches to avoiding NoSQL injection.

LDAP Injection
One method to inquire about the users and devices on a system is through the Lightweight Directory Access Protocol (LDAP). One example is its usage in Active Directory queries on Microsoft's part. Attackers can send specially constructed inputs that create harmful effects when applications employ untrusted input in LDAP searches. An attacker can manipulate directory data by using LDAP injection to evade authentication. To avoid LDAP injection, you can make use of parameterised queries.

Log Injection
If you want to keep an eye out for any suspicious activity on your network, you should implement system logging. However, have you ever thought that the information in your log files might be misleading you? Criminals could potentially alter log files in the same way they alter other system files. In order to hide their tracks, attackers frequently alter log files. An attacker can alter your log files in several ways, one of which is by log injection. This occurs when an attacker manipulates your application to insert false entries into your log files.

When the program fails to sanitise input written to logs in Java, log injection frequently occurs. By inserting new entries into application logs, attackers can take advantage of the new line character. Another method by which attackers can take advantage of user input in logs is by inserting malicious HTML into log entries. This could be done in an effort to trigger an XSS on the administrator's browser.

You must be able to differentiate between legitimate log entries and those that an attacker has inserted to avoid log injection attacks. One approach would be to include additional metadata, such as a timestamp, process ID, and hostname, at the beginning of each log entry. In addition, you shouldn't view or operate on the contents of log files without first validating them, since they contain untrusted input.

Mail Injection
Depending on the user's behaviour, a lot of web apps will send them emails. If you subscribed to a news feed, for example, the website may confirm your subscription by sending you an email including the feed's name.

Injection of user-supplied email addresses occurs when an application uses such addresses to send emails. As a result, fraudsters may be able to exploit your email account to launch social engineering efforts or mass email spam campaigns using your server.

Template Injection
A web page's appearance can be determined using template engines, which are a kind of software. Developers have a means to determine the rendering of a page by mixing application data with web templates; these templates are authored in template languages like Jinja. When building websites, developers can use web templates and template engines to keep client-side presentation code distinct from server-side application logic.

By "template injection," we mean inserting code into pre-made web pages. The template injection vulnerability could allow attackers to view sensitive data, run code, or elevate their levels of access on the system, according to the permissions of the affected application.

Expression Language Injection
A programming language known as expression language (EL) is code that is executed as code in Java Server Pages (JSP). It is possible for attackers to incorporate malicious code into these expressions when they receive untrusted user input. The expression language interpreter could then launch this code. As a result, remote code execution occurs.

Avoid using expressions evaluated by the EL interpreter with untrusted user input to prevent EL injection. To avoid having data interpreted as code, either encrypt the data or use an allowlist to check it before passing it into an EL expression.

Regex Injection
To define a search pattern in text, one uses a regular expression, known as a regex. In certain cases, users are able to submit their own regular expression patterns into the application, which the server can then execute or utilise to develop a regex. When an attacker feeds a regex engine a pattern that takes too long to assess, it's called a regex injection attack or a regular expression denial of service (ReDoS).

Fortunately, regex injection may be safely avoided by not using user input to generate regex patterns and by building well-structured regex patterns whose calculating time does not increase exponentially with the length of the text string.

XPath Injection
One query language that XML documents make use of is XPATH. Consider XML as SQL. To access and manipulate data contained in XML documents, one uses XPATH. To get the salary data from an XML file, for instance, you can use XPATH. You can also use it to compare or operate on the data numerically.

An attack known as XPATH injection modifies the query's result by inserting code into XPATH expressions. Attacks such as these, similar to SQL injection, can compromise sensitive information, bypass business logic, and elevate user privileges. Applications are particularly susceptible to XPATH injections in areas where XML is used to transmit sensitive data between systems and online services. Using parameterised queries is a good way to avoid SQLi, just like SQL injection.

5. Sensitive Data Leaks

A sensitive data leak happens when an app doesn't adequately safeguard sensitive information, allowing unauthorised users to gain entry to the data. Data such as software version IDs, internal IP addresses, confidential filenames, and file paths are examples of technical details that could be used in an attack. Additionally, it may contain the application's source code, which would enable hackers to analyse the application's code. On rare occasions, the program shares sensitive user data like email addresses, mailing addresses, and bank account details.

If an application spills private technical information, it's usually via error logs with stack traces or database errors, open directory entries on the platform's file system, and comments in HTML and template files that are easy to read.

6. Authentication Bypass

The process of verifying one's identity prior to carrying out sensitive operations or gaining access to sensitive data is known as authentication. Attackers can acquire access to features they shouldn't have if authentication isn't properly established on an application.

7. Improper Access Control

Inadequate access control is at the heart of authentication bypass difficulties. Any time an application's access control is constructed in a way that an attacker may easily overcome it, we say that it is incorrectly implemented.

Authentication is just one part of access control, though. A user is asked to show their identity in authentication, which asks, "Who are you?", whereas the program is asked, "What is this user authorised to do?" in authorisation. Users' inability to access features outside their authorisation levels is a result of strong authentication and authorisation procedures working in tandem. Many methods exist for setting up user authorisation, such as ACLs, role-based ACLs, ownership-based ACLs, and more.

8. Arbitrary File Writes

Attacks that allow arbitrary file writes function in a manner analogous to directory traversals. An attacker might potentially replace existing system files or create new ones on any path they like if an application sends files to the underlying machine and uses user input to determine the output file name. Critical system files, such as log files or password files, might be altered by hackers, or their executables could be added to script folders.

To reduce the likelihood of this happening, you should avoid generating file names using the user's session data, HTTP input, or any other information that the user can modify. The path, extension, and name of each newly created file should be under your control. When the user has to create a new file, for example, you can make up a random string of letters and numbers to use as the name. Before file creation, you can additionally remove special characters from user input.

9. Denial of Service Attacks

Attacks that disrupt the target machine's services in order to prevent legitimate users from accessing them are known as denial of service (DoS) attacks. In a denial-of-service attack, the attacker tries to overwhelm the server by flooding it with HTTP requests, crashing processes, or using all of the server's resources.

It is difficult to protect against denial-of-service attacks. Making things as tough as possible for would-be attackers is one technique to lessen your vulnerability. To stop logic-based DoS attacks, you can restrict specific file types and set size limitations with a firewall that provides DoS security.

10. Cross-Site Request Forgery

One method that can be employed by clients to compromise other users of a web application is cross-site request forgery (CSRF). Attackers can use cross-site request forgery (CSRF) to steal sensitive information by sending HTTP requests that appear to originate from the target. Without your knowledge or consent, a hacker could alter your password or withdraw funds from your bank account.

Avoiding state-changing operations via GET requests and utilising a mix of CSRF tokens and SameSite cookies is a certain technique to prevent cross-site request forgery (CSRF), in contrast to open redirection.

11. Server-Side Request Forgery

An attack known as Server-Side Request Forgery (SSRF) occurs when a malicious actor impersonates a legitimate server and sends requests on its behalf. Vulnerable servers can have their request signatures "forged" by attackers, giving them access to internal services, a privileged position on the network, and the ability to evade firewall protections.

An attacker might potentially access secret admin panels, read confidential files, and make API calls to the vulnerable server, depending on the permissions granted to it. Never send outbound queries depending on user input; it's the simplest approach to avoid SSRF issues. You should verify the addresses before sending out the request if you must use user input to make outbound requests.

12. Trust Boundary Violations

"Trust boundaries" are the points at which untrusted user input becomes part of a regulated system. In the absence of server validation, an HTTP request, for example, is regarded as untrusted input.

When storing, transporting, and processing data, make sure to differentiate between trusted and untrusted sources. When people fail to recognise and separate trusted from untrusted data, a breach of trust occurs. For example, the program may begin to mistake trusted and untrusted data if they are stored in the same database or data structure. This can lead to the incorrect conclusion that unreliable data has been validated.

Final Remarks

For maximum security, it's best to validate user inputs before using them. It's convenient to put the responsibility on the front end, but they're merely a first line of defence that might fail.

Even though Java can serve as both the frontend and the backend at the same time, it is still wise to verify that the user-provided data matches your expectations. Instead of attempting to discover and remove every possible thing, it may be sufficient to simply identify and indicate what is allowed when setting up your validation settings.