If you’re managing an SIEM (Security Information and Event Management) system, you know how vital centralized threat detection is.
SIEM collects and analyzes data from multiple sources—your firewalls, applications, servers—and looks for patterns that could be a security threat.
But here’s the thing: relying only on pre-built rules is like a one-size-fits-all approach to security. It will catch some obvious threats but not enough to give you full coverage.
In this article, we’ll explain why default SIEM rules fail and how customizing them can make all the difference. You’ll also see why aligning your SIEM with the MITRE ATT&CK framework is key to detecting real multi-stage threats.
Correlation Rules in SIEM
At its heart, a SIEM system is designed to collect, analyze, and alert. It works by using correlation rules that act as triggers when certain patterns are found in the data.
For example, if an unusual login attempt occurs, it will trigger an alert based on a pre-built rule. This allows security teams to focus on actionable insights rather than digging through massive amounts of raw data.
But, the truth is that most legacy SIEMs focus too much on generating alerts from individual events.
They don’t go far enough in connecting the dots between seemingly unrelated alerts to show you the full scope of the security threat.
If your SIEM isn’t configured correctly your team will be overwhelmed with alerts and miss the attack hidden in the noise.
Default SIEM rules
Most SIEM solutions come with default rules to get you started, but these are just that—a starting point. If you’re relying solely on these out-of-the-box rules, you could be facing:
- Rule duplication and coverage gaps
Pre-built correlation rules often overlap in functionality. It isn’t inefficient as the same types of alerts are triggered by multiple rules. Worse still these rules may not even cover all the tactics and techniques used by advanced attackers. The result? Gaps in your threat detection.
- Quantity over quality
You might think the more rules the better but that’s not always the case. Some vendors offer thousands of rules but many are irrelevant or poorly tuned for your environment. When rules prioritize quantity over quality it can lead to an overwhelming number of alerts—many of which are false positives.
- False positives everywhere
Enabling too many generic rules means a flood of false positives. Every alert needs to be investigated which takes up valuable time and resources. Over time, dealing with false positives will burn out your security team, and real threats will go undetected.
- Slow and painful onboarding
Setting up a SIEM system takes time, and getting it tuned to your environment takes even longer. Whether you’re doing it in-house or working with a Managed Security Service Provider (MSSP), onboarding and configuring all those rules can take days or weeks and delay your ability to respond to threats.
- Inconsistent rule updates
Once your SIEM is up and running, you need to keep the rules updated. However, for MSSPs managing multiple clients, updating rules for one environment doesn’t automatically apply to others. This lack of consistency means inefficiency and security gaps across different environments.
How SOC and MSP/MSSP solve these challenges
Why aligning with the MITRE ATT&CK framework matters
To improve your SIEM system’s threat detection, you need to align it with the MITRE ATT&CK framework. This framework breaks down the techniques and tactics attackers use so you have a complete view of how attackers operate. Most default SIEM setups only cover about 20% of the MITRE ATT&CK framework. It means you’re missing key attack stages like privilege escalation or lateral movement.
By aligning your SIEM rules with MITRE ATT&CK, you can achieve 90% coverage. This means you’ll catch more advanced attacks and reduce the noise from false positives. Instead of being overwhelmed by false positives, your team can focus on the threats that matter.
Customizing your SIEM: The benefits
So, what do you get by moving beyond default rules and customizing your SIEM?
- Better threat detection
When you customize your SIEM rules, you’re not just reacting to individual events—you’re detecting multi-stage attacks. It means you’re not missing the bigger picture and you can respond to threats more effectively.
- Fewer false positives
Custom rules allow you to filter out the noise so you are only alerted to what matters. Fewer false positives mean your team spends less time on wild goose chases and more time on real threats.
- Faster incident response
Customizing your SIEM not only improves detection but also speeds up response times. When tuned, your system can reduce response times by up to 42% for critical alerts. That’s a big difference in minimizing the damage from an attack.
- Faster onboarding
A well-tuned SIEM can cut onboarding time from weeks to days if you have multiple clients or environments. Thus, you can get up and running quickly so threats are detected and dealt with quickly.
Solving SIEM challenges: Real-world examples
Do you want to know just how much of a difference custom SIEM rules can make? Let’s take a real-world example to show you.
A Managed Security Service Provider (MSSP) used the out-of-the-box SIEM solution. Like most organizations, they used the 500 pre-built correlation rules that came with the system.
These rules were a good starting point, but they noticed some severe limitations as the MSSP grew and took on more clients. The system was catching some threats, but not all of them.
Their security team found that many important incidents were being missed or buried under a mountain of noise.
To address this, the MSSP decided to optimize their SIEM system for performance. They started by evaluating the effectiveness of the 500 built-in rules and then customized and enhanced them for their clients’ environments.
This wasn’t just a superficial update—they aligned their custom rules with the MITRE ATT&CK framework, which provided a more robust and comprehensive approach to threat detection.
As part of this optimization, they added 275 new rules, each one designed to catch threats that the default rules were missing. These new rules were designed to improve threat detection and reduce the number of false positives that were overwhelming their security analysts.
The results were dramatic.
Here’s what they got:
- MITRE ATT&CK coverage increased from 20% to 90%
- With the custom rules, they were able to detect a much more comprehensive range of sophisticated attacks that were previously invisible. The alignment with MITRE ATT&CK meant they could now track attackers through multiple stages of an attack, not just isolated events.
- Response times to critical alerts dropped 42%, and response times to high severity alerts 29%
- Custom rules meant security teams no longer had to wade through a mountain of noise. With fewer false positives, they could respond faster to real threats and minimize the damage from an attack. Critical alerts—those that are the most immediate and serious—were responded to almost twice as fast, a big win for their clients’ overall security.
- Onboarding time for new clients reduced from 7-10 days to 1-2 days
- Before the custom rules were implemented, onboarding new clients required extensive setup and tuning of the SIEM system to meet each environment’s unique requirements, which could take up to 10 days. After they optimized their system, onboarding became much smoother and faster. By applying pre-customized rules that had been refined for various environments, they could onboard new clients in 1-2 days and get them protected and valued faster.
These changes improved the security of the SIEM system, but they also had a domino effect across the whole process—simplifying things for existing clients, reducing the workload on security analysts, and making the whole system more efficient and scalable.
For example, the reduction in false positives meant analysts could focus on real threats, not just response time but the overall quality of the security service. By reducing the noise and refining the system to match the actual threat landscape their clients faced, the MSSP was able to better protect organizations from multi-stage sophisticated attacks.
This wasn’t just about detection and response times. It was also the foundation for more automated and proactive threat management, where the SIEM could predict attack patterns based on known behaviors from the MITRE ATT&CK framework.
With this level of customization, the SIEM was no longer just a reactive tool—it was a proactive defense mechanism that could handle current and future threats in real-time.
By taking the time to customize their SIEM and align it with established threat frameworks, the MSSP improved security performance and overall service delivery, and their clients felt more secure.
Managed Services by UnderDefense
UnderDefense provides managed services that fit your budget and give you confidence in your organization’s security posture. Here’s how our services can help you overcome common challenges:
- Immediate, personalized support: 24/7 access to dedicated analysts who know your business and get back to you fast.
- Comprehensive attack detection: Beyond 24/7 monitoring, we detect threats proactively providing context and remediation advice.
- Tooling optimization: We tune your security tools to reduce alert noise by 82% and integrate with all your existing tools for a single pane of glass.
- Customer ownership: You own all fine-tuned tools and processes at the end of the contract so you have control and value.
- Operational transparency: Full visibility into alert timelines, threat context, and regular reports.
Conclusion: Don’t settle for default
At the end of the day, a SIEM system is only as good as the rules that power it. If you rely solely on out-of-the-box correlation rules, you’re leaving gaps in your security that can be easily exploited.
By customizing your SIEM, aligning it to frameworks like MITRE ATT&CK, and keeping rules up to date, you can make a big impact on your threat detection.
How to Choose an ultimate Managed SIEM solution for Your Security Team -> Download Free Guide(PDF)