Honest Purple Teaming: How to Design Exercises That Surface Real Gaps Instead of Confirming Assumptions
The phrase "purple team exercise" now appears in security budgets, board presentations, and vendor pitches with enough frequency that it has begun to lose meaning. In theory, purple teaming represents one of the most valuable practices available to a mature security organization: a structured collaboration between offensive and defensive practitioners designed to test detection and response capabilities against realistic attack scenarios. In practice, many exercises devolve into scripted performances that confirm existing assumptions, generate polished reports with predictable findings, and leave both teams feeling validated rather than challenged.
This is not a criticism of the concept—it is a criticism of how the concept is commonly implemented. When purple teaming works, it is genuinely among the highest-return activities a security team can undertake. The question is what separates exercises that drive real improvement from those that produce theater.
The Structural Problems That Undermine Most Purple Team Engagements
Before examining what good looks like, it is worth diagnosing why so many exercises fall short. Three failure modes recur consistently across organizations of varying size and maturity.
The Detection Confirmation Trap Many purple team scenarios are designed around techniques the blue team already knows how to detect. This happens partly because scenario selection defaults to well-documented attack patterns, and partly because blue team leads, consciously or not, shape the exercise toward their existing coverage. The result is a session that validates what works rather than exposing what does not. A purple team exercise that never produces a missed detection has almost certainly been designed incorrectly.
The Attendance Problem Purple teaming requires genuine, real-time collaboration between red and blue practitioners. When exercises are run as sequential handoffs—red team attacks, blue team reviews the results afterward—the collaborative learning loop breaks down. The blue team loses the opportunity to observe technique execution in context, and the red team loses the feedback that would allow them to adapt their approach based on what the defensive tooling actually sees.
The Reporting Disconnect Exercise findings frequently fail to translate into remediation action because the output is structured as a narrative report rather than an operational backlog. Security leadership reads the executive summary, files the document, and the specific detection gaps identified during the exercise remain unaddressed six months later because there is no mechanism connecting findings to engineering work.
Designing Scenarios That Challenge Rather Than Confirm
Effective scenario design begins with threat intelligence, not tool capability. The question driving scenario selection should be: what techniques are threat actors targeting organizations in our sector actively using, and which of those techniques do we have the least confidence in detecting?
For US-based organizations, sector-specific threat intelligence is available through ISACs (Information Sharing and Analysis Centers) and FBI and CISA advisories. Starting with this material grounds your scenario design in actual adversary behavior rather than generic attack frameworks.
Once you have identified a technique cluster—credential dumping, kerberoasting, and pass-the-hash are a common starting point for Active Directory environments—build scenarios that chain techniques together in the sequence an attacker would realistically use them. Single-technique tests have limited value; what matters is whether your detection and response capability holds up across a multi-stage attack sequence.
Critically, build in at least two scenarios per engagement where you have low confidence in your detection coverage. These are uncomfortable to run because they frequently result in the blue team missing the activity entirely. That discomfort is the point. Exercises that only test what you know you can detect are not exercises—they are demonstrations.
Establishing Rules of Engagement That Keep Both Teams Honest
The rules of engagement document is where most of the behavioral incentives of a purple team exercise are set. A poorly written ROE creates conditions for the detection confirmation trap and the attendance problem simultaneously.
Several specific provisions improve exercise integrity.
Require real-time blue team observation. Red team operators should execute techniques with a blue team analyst watching alongside them—not reviewing logs afterward, but observing the execution environment and the SIEM simultaneously. This surfaces the gap between what an attacker does and what the detection layer sees, in real time.
Prohibit technique telegraphing. The red team should not announce which specific technique they are about to execute before executing it. Giving the blue team advance notice transforms a detection test into a confirmation test. The ROE should specify that technique selection remains with the red team throughout the exercise, with the blue team notified of the general scenario context but not the specific execution path.
Define a "stop and discuss" protocol. When a technique executes without generating an alert, the exercise should pause for a structured discussion before moving to the next technique. This is where the collaborative learning actually happens. Document what the blue team expected to see, what the red team observed in the detection tooling, and what the gap reveals about the detection logic.
Include a mandatory missed-detection threshold. If an engagement concludes without any missed detections, the red team lead should document explicitly why every technique was detected. This creates accountability for scenario selection and prevents exercises from drifting toward only testing covered ground.
Executing the Engagement Without Losing Momentum
Purple team exercises have a tendency to stall in the planning phase. Scenario design expands, scheduling conflicts multiply, and the engagement that was supposed to happen in Q1 becomes a Q3 discussion. Maintaining momentum requires constraining scope deliberately.
A focused two-day exercise covering four to six technique chains produces more actionable output than a sprawling two-week engagement that attempts comprehensive coverage. Prioritize depth over breadth. It is more valuable to thoroughly understand why a specific lateral movement technique went undetected than to superficially test twenty techniques and document partial findings on all of them.
For organizations without dedicated red team staff, external partners can fill the offensive role. When engaging external practitioners, ensure the ROE explicitly requires knowledge transfer during execution—not just a findings report afterward. The collaborative observation model requires the external team to operate transparently rather than in isolation.
Translating Findings into Operational Change
The output of a purple team exercise should not be a PDF. It should be a structured set of detection engineering tasks, each tied to a specific technique, a specific gap in the detection logic, and a specific remediation action.
For each missed detection, document the following: the technique executed, the data source that should have generated relevant telemetry, why the existing detection rule failed to fire or did not exist, and the specific engineering change required to address the gap. This format maps directly to a security engineering backlog and creates accountability for follow-through.
Schedule a validation run thirty to sixty days after the primary exercise to confirm that remediation actions were implemented and that the previously missed techniques now generate appropriate alerts. Without this validation step, the exercise produces findings that age without resolution.
Purple teaming done honestly is uncomfortable. It reveals gaps that nobody wants to report upward. But that discomfort is precisely what distinguishes a program that improves from one that merely appears to.
