Purple Teaming: What Happens When Red and Blue Finally Work Together

The assumption baked into most offensive security engagements is that the red team and the blue team should not talk. The red team attacks. The blue team defends. The simulation is realistic when neither side knows exactly what the other is doing. That structure makes sense for a full red team engagement designed to test whether your detection and response capabilities would catch a sophisticated adversary.

It is not the right structure for most organizations. Most organizations have not validated whether their detections work at all, and the answer to that question does not require eight weeks of covert adversary simulation. It requires sitting red and blue team members in the same room, running attack techniques one at a time, and watching together to see what fires.

That is purple teaming. It is less dramatic than a covert red team engagement, considerably cheaper, and often produces more actionable improvement in detection coverage.

What Purple Teaming Actually Is

A purple team exercise is a structured collaboration between offensive and defensive capabilities where the goal is not to simulate a realistic attack without being detected but to systematically validate and improve detective controls against specific attack techniques.

The name comes from mixing red (offensive) and blue (defensive), which is obvious to the point of being slightly embarrassing, but it describes the relationship accurately. Purple teaming is collaborative rather than adversarial. The red team member executes a specific technique, openly, while the blue team member watches the detection tooling and reports what they saw. The conversation is the point.

Did the endpoint detection tool fire on that? What did the alert look like? What context did it include? Would an analyst looking at this alert know what to do next? If nothing fired, why not? Is the log source configured? Is the detection rule actually active? Is it tuned so aggressively it would never fire on this behavior?

These questions get answered in an afternoon instead of after a debrief at the end of an eight-week engagement.

How It Differs from a Red Team Engagement

A covert red team engagement tests whether your detection and response capabilities work under conditions resembling a real attack. It is a valuable test, and it belongs later in a security program's maturity arc. The simulation is only meaningful if there are capabilities to test. An organization that has not validated its detection coverage has nothing worth testing covertly.

Purple teaming validates whether the coverage exists. It is the step before the red team exercise, not a replacement for it.

The difference in information density is significant. A red team engagement ends with a report that tells you which techniques went undetected. That is useful. A purple team session tells you, in real time, why a technique went undetected - what log data existed but was not collected, what rule existed but was incorrectly scoped, and what the detection gap actually is in enough detail to fix it the same week.

What a Session Actually Looks Like

Most purple team exercises are structured around a framework like MITRE ATT&CK, which documents adversary techniques in enough detail to operationalize them as discrete test cases. You pick a set of techniques relevant to your threat profile, typically techniques used by adversary groups that target your industry, and work through them methodically.

The session structure is straightforward. The red team executes a technique - say, credential dumping via LSASS memory access. Everyone watches the detection tooling. The blue team calls out what fired, what the alert contained, and whether they would have acted on it without the context provided by the session. The red team and blue team discuss what was missing or what was noise. Adjustments get logged. Move to the next technique.

In a two-day session, a small team can work through thirty to fifty techniques. A traditional red team engagement might cover some of those same techniques across eight weeks, and you get the gap list at the end rather than as you go.

What Good Coverage Actually Means

One thing purple team exercises consistently surface is the difference between a detection rule existing and a detection rule working. Organizations with mature SIEM deployments often have hundreds of detection rules. Many were written years ago against different log sources, tuned for conditions that no longer match the environment, or suppressed because they were generating noise and nobody got around to fixing the underlying issue.

A rule that fires correctly on the simulated technique, generates a useful alert with enough context for an analyst to triage it, and maps to a documented response procedure is a working detection. A rule that exists in the SIEM but is set to generate informational events with no alert is not a detection. Both show up the same way in a control inventory. They show up differently when you run the test.

Purple teaming also validates log coverage, which is frequently a bigger gap than detection rules. You cannot detect what you are not logging. Running an attack technique and finding no alert is sometimes a gap in the detection logic. More often it is a gap in log collection: the relevant Windows event log was not being forwarded, the EDR agent was not deployed on that class of host, or the network tap did not cover that segment.

Who Gets the Most Out of It

Purple teaming is most valuable for organizations that have deployed detection tooling but have not systematically validated it. If you have a SIEM with ingested log sources, an EDR platform, and some detection rules, but you have never confirmed that specific attack techniques actually generate alerts and those alerts are actually actionable, you have an untested program. Purple teaming answers that question.

It is also valuable when deploying new detection infrastructure. A purple team session run against a freshly deployed EDR platform tells you how it performs against real techniques in your specific environment before you depend on it to catch a real attacker.

What it is not suited for is organizations whose primary need is a realistic adversary simulation to validate mature detection and response capabilities. That is the red team engagement, and it remains the right tool for that specific question.

The Practical Case

Purple teaming does not require a large external engagement. An internal security team with some offensive tooling and a clear testing structure can run sessions against their own detections. External teams offer the advantage of bringing techniques the internal team is less familiar with and an outside perspective on what detection gaps look like from the attacker's point of view.

Either way, the output is specific: a list of tested techniques, which generated reliable alerts, which generated partial or noisy signals worth tuning, and which generated nothing and need new coverage. That list becomes the detection engineering backlog, prioritized by the techniques most relevant to your actual threat profile.

A security program that has validated its detection coverage through systematic testing is in a meaningfully different position than one that has deployed tooling and assumed it works. Purple teaming is the shortest path from one to the other.