Why Red Team Attacks Fail Inside Your Own Firewalls

In today’s threat landscape, siloed security functions are a liability. The traditional model, where a red team runs covert attacks and the blue team chases alerts, often leaves critical gaps between offensive findings and defensive fixes. To truly fortify your organization’s resilience, a collaborative approach is paramount. This strategic guide details how to build purple team SIEM penetration testing capabilities, merging attacker tradecraft with defender tooling to create a living feedback loop that continuously validates and improves your detection and response posture.

What is a Purple Team and Why Modern Enterprises Need One

Purple teaming is a collaborative, transparent process where offensive and defensive security teams work together with the singular goal of improving detection and response capabilities. As defined by one researcher in a recent lab series:

Purple Teaming is collaborative “open-book” testing between offensive/red and defensive/blue teams, with the goal of evaluating activity to identify and remediate potential security gaps.

The core value proposition is direct and powerful. Traditional red team engagements, while critical, have a structural flaw: they operate covertly, delivering a report weeks later. This creates a slow, indirect feedback loop where defenders must reverse-engineer detections from written descriptions of past activity. A security consultant highlights the resulting inefficiency, stating nearly 6 in 10 red team findings never get actioned by the blue team when the two functions operate separately.

Purple teaming collapses this latency to near zero. By executing attacks in the open while defenders watch their SIEM (Security Information and Event Management) and EDR (Endpoint Detection and Response) consoles in real-time, teams can immediately identify what was missed, why, and how to fix it. This collaborative model directly translates to stronger security outcomes; organizations using this style of collaboration report far stronger detection rates against ransomware than those that keep red and blue apart.

Core Components: People, Processes, and Technology Stack

Building an effective internal purple team hinges on integrating three foundational elements: the right people, structured processes, and a practical technology stack.

People: The goal is not to hire a new, distinct "purple team." Instead, it's about fostering collaboration between existing roles. Key skills to cultivate include adversary emulation (for building realistic attack chains), detection engineering (to turn findings into working SIEM rules), threat intelligence (to align tests with relevant threats), and, critically, communication to bridge the operational and cultural divides.

Processes: A formalized workflow transforms ad-hoc collaboration into a program. The essential process is a cyclic feedback loop: execute a technique, check for alerts, tune detections if needed, and validate the fix. This should be mapped to a maturity model, which typically progresses from Ad hoc (rare, uncoordinated testing) to Coordinated (scheduled exercises) to Structured (formal metrics and feedback loops), and ultimately to Continuous (ongoing, often automated testing).

Technology Stack: The lab environment is where theory meets practice. A functional purple team detection lab does not require a massive budget; it can be run on a single machine with sufficient resources. The architecture should prioritize:

• Isolated Networks: Segment attack platforms from target environments.
• Full Telemetry: Ensure target hosts forward comprehensive logs (e.g., via Sysmon, Elastic Agent) to your SIEM.
• Resettable Snapshots: Use VM snapshots to revert to a clean state quickly after each test.
• Realistic Environments: Populate test domains with tools that mimic real-world Active Directory setups.

At its heart, the core technology stack revolves around two pillars: the offensive tools to emulate adversaries and the defensive platforms, primarily the SIEM, used to observe and analyze the resulting activity.

Step 1: Selecting and Integrating Red Team Tools

The red side of your purple team needs structured, repeatable ways to emulate adversary behavior. The focus should be on frameworks that map clearly to defensive telemetry and the MITRE ATT&CK framework, providing a common language for both teams. Based on current practitioner recommendations, three primary tool categories are essential.

1. Atomic Testing Frameworks: For granular, technique-level testing, Atomic Red Team is the "unit testing framework for detection." It allows you to execute a single ATT&CK technique (e.g., credential dumping via Mimikatz) in isolation, which is perfect for validating specific detection rules. Teams can invoke tests via PowerShell (Invoke-AtomicTest T1003.001) and generate inventories for planning.

2. Adversary Emulation Platforms: For testing full attack chains, MITRE Caldera is a prominent option. It allows you to build "adversary profiles" that string together techniques to mimic real threat actor playbooks, such as APT29. Its native ATT&CK mapping and built-in reporting are strengths, though it requires managing agent deployment.

3. Command & Control (C2) Frameworks: For the most realistic emulation of post-exploitation activity, a real C2 framework is invaluable. Sources mention tools like Sliver and Cobalt Strike. These frameworks test the full detection stack against actual beaconing, command execution, and lateral movement. A critical legal warning accompanies these tools: they are dual-use and must only be deployed in isolated lab environments you own, with explicit authorization. Unauthorized use is a felony.

Legal notice: C2 frameworks like Sliver, Cobalt Strike, and Mythic are dual-use tools. Only deploy them in isolated lab environments you own. Unauthorized use is a felony under the CFAA and equivalent laws globally.

The key is to choose tools that align with your threat model and skill level. For beginners, Atomic Red Team provides a low-barrier entry. As maturity grows, integrating Caldera or a C2 framework provides the realism needed to test detection across multi-stage campaigns.

Step 2: Configuring Blue Team Tools (SIEM & EDR)

The blue side’s primary observation post is the SIEM, augmented by EDR telemetry. The SIEM serves as the "single source of truth" for measuring detection coverage. Without structured SIEM telemetry, purple teaming becomes subjective guesswork.

The configuration goal is to ensure the SIEM provides three critical capabilities for exercises:

1. Raw Log Completeness: Every red team action must generate a log event that reaches the SIEM.
2. Alert Generation Fidelity: Correlation rules must fire accurately when specific techniques are executed.
3. Retention & Queryability: Analysts must be able to search historical data and export metrics efficiently.

For practical lab setups, sources recommend prioritizing EDR as the main data source because it provides "the highest value and offers the most comprehensive view of any single data source." EDR agents collect critical telemetry on processes, file system, registry, network, and memory. Since this data is often forwarded to a SIEM, the querying skills developed are transferable.

A key consideration is log retention. Sources warn that if your SIEM does not retain raw logs for at least 90 days, purple teaming loses historical comparison value, making regression analysis impossible.

Step 3: Establishing the Feedback Loop: From Attack Simulation to Alert Tuning

This is where collaboration becomes operational. The purple team feedback loop is a disciplined, iterative cycle that treats detections like code, tested, validated, and improved. A consultant outlines the real-time session workflow:

• Technique Selection: Teams agree on a prioritized list of ATT&CK techniques to test.
• Execution: The red team executes the technique on a designated test system.
• Detection Check: The blue team checks for alerts in the SIEM/EDR within 5-10 minutes.
• Rule Development: If no alert fires, the blue team writes a detection rule on the spot using the actual logs generated.
• Validation: The red team re-executes the technique to confirm the new rule works.
• Coverage Mapping: The technique is marked as detected, not detected, or needing tuning on an ATT&CK heatmap.

The technical workflow for detection engineers typically involves these steps:

1. Select a Technique: Use threat intelligence and audit existing SIEM rule coverage to find gaps.
2. Emulate the Technique: Execute it in the lab, documenting commands and expected telemetry.
3. Verify Telemetry: First, confirm the raw logs (e.g., Sysmon Event ID 10 for LSASS access) actually appear in the SIEM. A visibility gap must be fixed before a rule can be written.
4. Write the Detection Rule: Use a portable format like Sigma for cross-SIEM compatibility, then compile it to your SIEM's native query language.
5. Test, Validate, Iterate: Re-run the emulation. Check for true positives, false negatives, and false positives. Attempt to evade the rule, then improve it.

This emulate → detect → evade → improve cycle is the heartbeat of a mature purple team. Each iteration makes detections more resilient.

Scenario Walkthrough: Simulating a Phishing Campaign End-to-End

Let’s apply the framework to a common attack vector: a credential phishing campaign leading to internal discovery.

1. Scenario Scope: Adversary sends a phishing email with a link to a fake login page, harvests credentials, uses them for initial access, and performs internal discovery.

2. Red Team Execution (Mapped to ATT&CK):

• T1566.001 (Phishing: Spearphishing Link): Deploy a mock phishing page.
• T1110.001 (Brute Force: Password Guessing): Victim enters credentials.
• T1078 (Valid Accounts): Adversary uses stolen credentials to access the VPN/O365.
• T1082 (System Information Discovery): Run commands like systeminfo on the compromised endpoint.

3. Blue Team Observation & Gap Analysis:

• The SIEM should ingest logs from the email gateway (phishing link), web proxy (connection to fake page), authentication server (successful login from new location), and the endpoint via EDR (systeminfo execution).
• The team observes in real-time: Does the SIEM correlate the anomalous login with the subsequent discovery activity? Does an existing rule for systeminfo execution fire, or is it lost in noise from admin activity?

4. Detection Tuning: If the discovery activity went unflagged, the blue team writes a new Sigma rule. For example, a rule could look for systeminfo execution following a successful login from a suspicious geolocation not seen in the user’s baseline. They would use the exact process creation logs from the test to craft the rule logic, then validate it by re-running the red team actions.

Measuring Success: Key Metrics for Purple Team Effectiveness

Moving from subjective feel to quantitative proof is critical for program sustainability and executive buy-in. Key metrics, as derived from SIEM data and exercise logs, include:

Measurement matters: If you cannot measure your detection coverage, you cannot improve it systematically. A MITRE ATT&CK heatmap produced from validated purple team testing is one of the most credible security metrics a security team can bring to an executive conversation.

These metrics allow you to present statements like, "We detect X% of techniques used by threat groups targeting our sector, up from Y% last quarter", a far more powerful posture indicator than simply stating "we have EDR deployed."

Scaling the Program: From Ad-Hoc Exercises to Continuous Operations

The end goal is to evolve from scheduled, manual exercises to a continuous, integrated program. This scaling journey follows the maturity model outlined earlier and is enabled by two key enablers:

Automation: Manual testing doesn't scale. Automating the repetitive parts of the feedback loop is essential. This can include:

• Scheduled Atomic Tests: Using frameworks to run a subset of technique tests automatically on a weekly cadence against non-production systems.
• Automated Baseline & Regression Testing: Using the SIEM's capabilities (like behavioral baselines) to auto-generate pre-exercise profiles and safely replay attack telemetry to validate detection changes.
• Integration with SOAR: Connecting the SIEM to a Security Orchestration, Automation and Response platform can automate the alert triage and response steps observed during exercises.

Threat-Informed Defense: Continuous purple teaming must be guided by real-world threat intelligence. This "threat-informed defense" practice means prioritizing the emulation of techniques used by adversaries actually targeting your industry, ensuring your detection engineering efforts are focused on the highest-risk gaps.

Organizations that leverage AI and automation in security operations, according to research cited in the sources, report notably lower breach costs. In a continuous model, the purple team philosophy embeds itself into the security DNA, creating a self-improving defensive system.

Avoiding Common Pitfalls: Blame Culture and Tool Silos

Two major cultural and technical pitfalls can derail a purple team initiative.

Blame Culture: The exercise must be framed as a collaborative learning opportunity, not a test of individual or team competency. The red team's goal is not to "win" or remain undetected; it's to generate the telemetry needed to improve defenses. Leadership must actively foster a blameless culture where the focus is on fixing systemic gaps, not assigning fault.

Tool Silos & Visibility Gaps: Practitioners warn against focusing on trendy tools without ensuring the underlying data is available. A common example is writing custom Yara rules only to find you cannot execute them across your environment, or that the necessary memory artifacts aren't being collected. Avoid frustration by prioritizing foundational SIEM and EDR telemetry first. Ensure the data flows before investing heavily in advanced analytic tools that depend on it.

A prime example of this is Yara. While it’s an incredibly valuable project... many engineers don’t realize that executing custom Yara rules across an entire environment is often not possible until they attempt to do it.

FAQ

Is purple teaming the same as a penetration test or red team engagement? No. These are complementary exercises with different goals. A penetration test finds vulnerabilities to patch. A red team engagement simulates a real attacker to test detection and response covertly. Purple teaming is a collaborative, open exercise focused on testing and tuning specific detection rules in real-time within your SIEM and EDR.

When should a company start a purple team program? You can begin as soon as you have a functioning detection stack, a SIEM processing logs and an EDR deployed on endpoints. You don't need a large team; a single scheduled exercise testing a handful of common MITRE ATT&CK techniques is a strong starting point.

How often should purple team exercises run? Annual exercises are insufficient given the pace of threat evolution. The goal should be to progress toward continuous testing, where techniques are validated on a weekly or bi-weekly cadence, often aided by automation for repetitive tasks.

What are the prerequisites for effective purple teaming? The core prerequisites are centralized logging (logs from endpoints, network, auth), a working SIEM/EDR processing data in near-real-time, and detection engineering capacity (someone who can write and tune detection rules).

How do we track progress over time? Use a dedicated tool like VECTR (which offers a free community version) to log test cases, map results to MITRE ATT&CK techniques, generate coverage heatmaps, and track improvements across assessment cycles for executive reporting.

What's the biggest mistake teams make when starting? Attempting overly complex, multi-stage "exercises" without first mastering atomic, technique-level testing. Sources advise starting with simple, repeatable test cases using frameworks like Atomic Red Team to build foundational skills and processes before scaling up.

Bottom Line

Building an in-house purple team is a strategic investment that transforms security from a siloed, reactive function into a collaborative, proactive system. Grounded in the real-time feedback loop between attack simulation (penetration testing tools) and defensive observation (SIEM/EDR), it provides measurable, continuous improvement. Success hinges on integrating people and processes, starting with atomic tests in a controlled lab, systematically measuring coverage with metrics like ATT&CK coverage percentage, and relentlessly focusing on closing the specific gaps that real attackers would exploit. The ultimate outcome is not just a set of tuned alerts, but a demonstrably more resilient security posture that can confidently answer the critical question: "Do our detections actually work?"