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Log4Net and Log4j


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Application logging is a big deal. Keeping track of software issues in production needs to be a priority because it helps you gain insight and monitor the performance of your applications. Ultimately, it helps maintain a healthy and sustainable app. Some reasons for logging data about software issues include enhancing security, debugging, and analytics.

A logging framework generates the logs for an application. Logs play an essential role in troubleshooting and evaluating the performance of your application.

You can choose from many available logging frameworks. In this article, we explore using Log4net and Log4j, which are used with ASP.NET and Java, respectively.

What Is Log4net?

Log4net, initially created by NeoWorks, is an open-source logging framework for the .NET framework. NeoWorks built it on the Apache Software Foundation Log4j architecture and gave it to the Foundation in February 2004. Log4Net is built to be reliable, efficient, and extendable so .NET developers can log their applications using a standardized logging framework.

Various .NET logging frameworks exist, including Error Logging Modules and Handlers (ELMAH), NLog, Microsoft Enterprise Library, and NSpring.

What Is Log4j?

Log4j is a reliable, fast, and flexible open-source logging framework for Java applications. It’s highly configurable at runtime through an external file. First released in January 2001, Log4j is part of the Apache Logging Services Project. Many individuals, large organizations, and Internet of Things (IoT) applications use it today. In fact, almost all of our daily computer software incorporates it because of how good Log4j logs Java applications.

There are various Java logging frameworks, including tinylog, Logback, the Java logging API, and Simple Logging Facade for Java (SLF4J). Each of these frameworks has unique features, but Log4j stands out among them because of its more extensive user base.

Benefits of Log4net

  • It provides support for various .NET frameworks. This allows developers to log their various .NET applications.
  • Log4net watches for changes in its configuration file and dynamically applies modifications made by the developer. This feature allows developers to work quickly and efficiently without having to perform updates manually.
  • It sends output to multiple logging destinations or targets to collect logged information.
  • At the time of logging, Log4net can capture logging context data in a transparent way to the developer.

Benefits of Log4j

  • It’s highly configurable and simple to understand and use with your applications. It doesn’t have a steep learning curve, so developers can quickly get started with Log4j.
  • Having a logging framework lets developers debug applications faster by helping them detect bugs and crashes, which improves the product development cycle.
  • Logging is highly flexible, and you can set it to monitor various levels of log event severity, such as all (all messages), debug, info (important/informative messages), warn, error, off, and fatal.
  • Log4j can manage Java exceptions in your code.
  • You can send logging information to various destinations, such as a database, a file, a console, and a Unisys log. This feature is important for stack and error traces.

Limitations of Log4net

  • Adding a logging framework puts an extra load on your application, and as a result, it can slow down your application.
  • It’s prone to security vulnerabilities since it’s an open-source framework.
  • Adding Log4net increases your codebase, potentially creating scrolling blindness and causing you to get lost in your codebase.

Limitations of Log4j

  • Log4j can also slow down your application’s performance by adding extra load to your codebase.
  • It currently has a major security vulnerability, as described in the next section.

Log4j Security Vulnerability

A Log4j security vulnerability has drawn much attention recently, and of course, you do need to worry about it. Some people consider it one of the most significant security vulnerability bugs in computer history because it cuts across almost every system and application worldwide. These concerns are real because hackers exploit this security vulnerability daily. They’ve carried out malicious attacks on big tech companies and individual users who use Windows, Linux, and Apple applications.

How Does the Security Vulnerability Work?

This vulnerability allows unauthenticated remote code execution by an attacker within Log4j. An attacker provides a specially crafted string through various input vectors. When the vulnerable Log4j component parses and processes those vectors, the hacker can bypass restrictions and gain access to a computer system without a password. Once in the system, they can try to install malicious software or spyware or steal information and data, including passwords. The security vulnerability was discovered on November 24, 2021, but not publicized until December 9. By that time, well-known companies such as CloudFlare and Twitter had already been affected.

Companies Using Log4net

Many companies such as Comcast Corporation and government entities like the United States Army use the .NET framework for their applications and the Log4net framework for logging.

Companies Using Log4j

Various companies use Log4j, including some big names like Twitter, CloudFlare, Tencent, AlphaSense, and Intuit. The Log4j security vulnerability impacted most of these companies.

How to Mitigate the Log4j Vulnerability Risk

The most reliable way to protect yourself from this security vulnerability is to frequently update all your software applications or systems to the latest version of Log4j. At the time of writing this article, the current version of Log4j is 2.17.2.

Other methods of mitigating the risk include changing your passwords frequently. Strong passwords, two-factor authentication, and a virtual private network (VPN) will also help secure your application. However, none of these methods provides 100% protection. Therefore, we’re all at the mercy of companies updating their software.

Another reliable way to enhance security is to watch for software and system updates for your computers and devices. Keep everything updated because you never know which update might be the security fix for the Log4j vulnerability. Also, as a developer or company, knowing what’s in your development environment and why you’re using it will help mitigate the risk of being affected.


You’ve now learned about Log4net and Log4j, which are logging frameworks for .NET and Java, respectively. Although they look similar, each has its unique features. Log4j currently has a security vulnerability that has attacked big tech companies.

If you want to monitor your applications and receive log messages, I suggest using SolarWinds® Papertrail. Papertrail is easy-to-use log management software designed to analyze, tail, and search your log messages. It’s fast to set up, with powerful integrations, team visibility, and much more. Try it for free today.

Further Reading

This post was written by Jethro Magaji. Jethro is a frontend engineer passionate about the tech world and uses creative thinking to solve business problems with a user-centered approach.

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