With how fast software is changing these days, spotting and remediating vulnerabilities is no longer enough. Rather than dealing with threats as they arise, you need to think like an attacker in order to survive.
As the person responsible for application security, you aren’t just managing risk; you’re also setting the tone for how their organizations build, test, and ship secure code. From defining security policies to selecting the right tools and guiding developer behavior, you’re on the front lines of defense.
And attackers know this.
Malicious code isn’t conjured out of thin air. It’s a calculated insertion of logic meant to blend in, execute quietly, and achieve impact, whether that’s data theft, ransomware deployment, or complete system compromise. But here’s the good news: Malicious code follows patterns. When you understand the motivations and techniques behind it, you can build security strategies that disrupt it at every stage.
What Motivates an Attacker? Follow the Incentives
Attackers, like any other actor in a system, follow incentives. Most aren’t outright geniuses but rather strategic opportunists. Their motivations range from the economic to the ideological, but they often converge on a single point: exploiting vulnerabilities in software applications.
One of the most common incentives is financial gain. Cybercriminals embed trojan horses into software packages or plugins, allowing them to steal credentials, deploy ransomware, or sell access to compromised environments. This type of attack can be launched at scale using malicious packages uploaded to public repositories like npm or PyPI. Once downloaded and integrated into applications, these packages enable backdoor access, data exfiltration, and even full system control.
Others are driven by status or ideology. In the underground world, pulling off a successful exploit against a high-profile target earns prestige. Some attackers use malicious code to support political agendas, disrupting services or leaking information to support activist causes. And let’s not forget the curious hackers who view applications as puzzles, breaking them apart to see what makes them tick.
Why Certain Vulnerabilities Are So Tempting
To an attacker, not all vulnerabilities are created equal. The most attractive weaknesses are those that are easy to exploit, hard to detect, and capable of granting significant access. As the head of application security, understanding these preferences can help you prioritize remediation based on what attackers are most likely to pursue.
For example, the infamous Log4Shell vulnerability in Apache Log4j was a goldmine for attackers. It required minimal technical effort to exploit and granted remote code execution capabilities across a vast number of systems. Attackers could automate their scanning and exploitation, yielding vast payoffs with very little input. This is a textbook example of why attackers love low-effort, high-impact flaws.
Visibility also plays a role. Development environments, CI/CD pipelines, and internal toolchains are often overlooked in security strategies. These areas may have fewer protections, making them ideal entry points for malware. Additionally, the widespread use of open source libraries amplifies risk. A single vulnerable or malicious package can cascade through an organization’s software ecosystem, making it a high-leverage attack vector.
How Malicious Code Gets Deployed: A Playbook of Tactics
Malicious code doesn’t sneak in by accident. Rather, it’s placed with precision. Attackers use well-honed tactics to infiltrate trusted environments. By understanding their playbook, you can design proactive defenses that catch these techniques before they do damage.
One of the most common tactics is typosquatting. By publishing packages with names that are nearly identical to popular libraries, attackers rely on human error. A mistyped command or rushed install can result in pulling down a malicious package, which then installs malware to capture data or execute unauthorized actions. In more advanced cases, attackers may inflate download numbers or replicate GitHub metadata to make their fake package look more credible. Rather than relying on novel technology or pure skill, typosquatting takes advantage of human error, a common theme among opportunistic hackers.
On the other side, another popular approach is dependency confusion, which takes advantage of automation that isn’t closely monitored. This occurs when a public package shares the same name as a private internal dependency. If the package manager resolves to the public version, attackers can inject malicious logic into internal builds without ever breaching the perimeter. Similarly, repository jacking allows attackers to take control of abandoned or renamed repositories and serve malicious updates under the guise of trust.
Even the infrastructure around these attacks is evolving. Some threat actors now use blockchain platforms to distribute command-and-control (C2) instructions. By embedding malicious payloads in smart contracts, attackers evade traditional detection methods. These methods show how sophisticated, resilient, and stealthy malicious code has become.
Not Just Theories: Real-World Examples of Malicious Code in the Wild
To illustrate the real-world impact of these tactics, Checkmarx has researched a few prominent examples of malicious code in the wild. These stories not only reveal how attackers operate, but also provide actionable lessons.
Log4j / Log4Shell
One of the most prominent and widespread examples already mentioned above is the Log4Shell vulnerability that exposed a critical flaw in the Apache Log4j library. Attackers quickly weaponized the bug to achieve remote code execution across countless systems worldwide. Organizations scrambled to patch the flaw, but the ease of exploitation and broad dependency on Log4j meant that malicious code had already propagated widely before defenses could be mounted. The attack highlighted the dangers of over-reliance on open source software without sufficient visibility and governance.
Roblox npm Campaign
In August 2024, Checkmarx researchers uncovered a long-running campaign targeting developers in the Roblox ecosystem. Malicious npm packages such as “noblox.js” masqueraded as legitimate tools, often cloning names and descriptions of popular libraries. These packages contained payloads that enabled remote access, data theft, and even installation of additional malware. The campaign demonstrated how attackers exploit branding, developer trust, and the open nature of package repositories.
node-ipc Campaign
Malicious code with international implications came in March 2022 when the maintainer of the widely used npm package “node-ipc” intentionally introduced malicious code to protest Russia’s invasion of Ukraine. This act involved adding a new dependency, peacenotwar, which displayed protest messages, and incorporating a script that targeted users in Russia and Belarus by overwriting files on their systems with a heart emoji. The incident, detailed by Checkmarx, highlights the emergence of “protestware,” which is software modified to express political views, which raised concerns about the security and trustworthiness of open-source software dependencies.
How to Manage Malicious Code in the SDLC
The above examples are just a few in a long list, and with limited time and resources to effectively manage every single risk in the software development life cycle (SDLC), AppSec teams are vulnerable to hackers seizing the opportunity at the right place and time.
To mitigate these risks, the most effective defense is a layered one that anticipates attacker behavior. That starts with integrating security into every phase of the SDLC.
Start with Software Composition Analysis (SCA). SCA tools allow your team to inventory and evaluate third-party dependencies. Modern SCA goes beyond CVEs; it looks for signs of malicious code, like unusual update patterns, unfamiliar maintainers, and anomalies in package behavior. A robust SCA strategy helps prevent viruses and malicious code from ever entering your ecosystem.
Next, embed security into developer workflows. Use static and dynamic analysis (SAST and DAST) to identify trojan horses and insecure coding practices before code is pushed to production. Integrate these tools into developer environments and CI/CD pipelines so developers receive real-time feedback without slowing down velocity. Combine this with policy-driven guardrails to block builds or deployments that include high-risk packages or known malicious packages.
Technical controls are only part of the equation, though. Your developers are on the front lines of defense. Equip them with training to spot red flags in third-party libraries. Regularly simulate attacks like typosquatting or dependency confusion to keep your team sharp. Threat modeling exercises should include adversarial thinking. If you were an attacker, how would you get in?
Encourage a culture of healthy skepticism. Developers should feel empowered to question dependencies, validate package origins, and raise concerns about suspicious behavior. This vigilance pays off in dividends when combined with the right tools and policies.
Finally, reevaluate your organization’s risk tolerance. Not all applications are equal. High-value APIs and sensitive user interfaces require stricter controls than internal tools or sandboxed environments. Define and enforce risk-based policies so your team can focus on what matters most.
Strategy Over Sophistication
Attackers don’t need to outsmart your tools; they only need to find the one place where you trusted too much. Whether it’s a misnamed package, an outdated dependency, or an unmonitored CI/CD process, malicious code finds its way in through gaps in visibility, governance, and education.
Your power lies in anticipating those gaps. By combining SCA, SAST/DAST, developer training, and continuous threat modeling, you can turn your application security program from reactive to resilient. Malicious code may be clever, but with the right mindset and strategy, your defenses can be even smarter.
The goal isn’t perfection. The goal is to make your applications such a hard target that attackers move on. And in the world of application security, that’s a win worth securing.To navigate these challenges, Checkmarx offers complimentary access to the Gartner® report, Application Security Guide for Software Engineering Leaders. This comprehensive guide delves into the obstacles faced by software engineers, such as lack of correlation, visibility, and orchestration within the SDLC, and outlines four critical actions that engineering leaders can implement to modernize and enhance their application security strategies.