Purple Teaming Explained: Red and Blue Working as One

Purple teaming is a security exercise where your attackers and your defenders work the same test together, in real time. Nobody waits weeks to compare notes. The red team runs an attack technique. The blue team watches its own tools try to catch it. Both sides fix the gap on the spot. For a UK business trying to get real value from a security testing budget, that live feedback loop often beats a covert red team report that lands on a Friday.

What is purple teaming in cyber security?

Purple teaming brings red team attackers and blue team defenders into the same exercise, sharing what they see as the test happens. Rather than one side testing the other in secret, both teams treat the engagement as a shared learning exercise.

The name comes from mixing red and blue: offence and defence working as one function instead of two. MITRE maintains ATT&CK, the widely used framework of real-world adversary techniques. It treats purple teaming as a practical way to map specific attacker behaviour against what your monitoring actually catches, technique by technique.

That matters because a report that says “we got in” tells you less than a session that shows exactly which alert should have fired, and didn’t.

Purple team vs red team vs blue team: what actually differs

These three terms get used loosely, so it helps to separate them by what each one is trying to achieve.

A standard penetration test or red team engagement checks whether an attacker can get in. Purple teaming checks something different: whether your detection and response actually work once someone tries. Both questions are worth answering, but they are not the same question.

How a purple team exercise actually runs

Most purple team engagements follow a similar rhythm, built around specific techniques rather than a single end-to-end attack story.

1. Scope and threat profile. The team picks techniques relevant to your sector, often mapped to MITRE ATT&CK, based on how attackers actually target businesses like yours.
2. Execute one technique. The red side runs it against the live environment, for example a specific credential dumping method or a lateral movement trick.
3. Watch it land. The blue side checks its SIEM, EDR and logs in real time for any alert, and reports honestly if nothing fired.
4. Fix it together. Both teams discuss the gap immediately and tune a detection rule, alert threshold or logging setting.
5. Re-run and confirm. The same technique runs again to prove the fix actually works, not just that it should.

Then the exercise moves to the next technique on the list. A single day can work through several, since nobody is wasting time staying hidden.

Why the NCSC says purple teaming often beats red teaming on value

The UK’s National Cyber Security Centre has made a point that is easy to miss. Covert testing has a real cost, and that cost is coverage. In a blog on SOC metrics, the NCSC notes that “the covert nature of red teaming can more accurately mimic a real attack.” But it adds that purple teaming “can often provide better value to a SOC.” The time otherwise spent staying hidden gets redirected into testing more attack paths instead.

That is a useful, slightly uncomfortable point for anyone who assumes secrecy is always the gold standard. A red team engagement answers one question: would we have noticed a real attacker? A purple team exercise answers a broader one. How many of the ways a real attacker could get in do we actually detect? Nobody has to burn hours evading your SOC first, so the test covers far more ground.

Neither replaces the other outright. A fully covert red team still has a place, particularly when leadership needs an honest answer about whether staff would notice anything at all. But if the goal is building detection capability rather than testing whether people notice, purple teaming usually gets there faster.

Purple teaming in regulated UK and EU sectors

Financial services firms will already recognise the shape of this from regulation. CREST built STAR-FS with the Bank of England, the Prudential Regulation Authority and the Financial Conduct Authority. It extends the intelligence-led approach used in the Bank’s CBEST framework to a wider range of firms. The overhead is lower than a full CBEST engagement.

Across the EU, the European Central Bank runs a similar approach through TIBER-EU. Its dedicated purple teaming guidance, first published in 2022 and updated since, sets out how the approach fits into the closure phase of a TIBER-EU engagement. That way, the blue team gets structured value from a test that would otherwise stay entirely covert. More than twenty European jurisdictions now run some version of TIBER-EU.

You do not need to be a bank to borrow the idea. These frameworks just formalise what any business can do on a smaller scale. Build detection improvement into the test itself. Do not leave it as an afterthought in a PDF.

Common mistakes that undermine a purple team exercise

Treating it as a red team with an audience. Some providers run the same covert playbook and simply narrate it afterwards. That skips the entire value: the live tuning has to happen technique by technique, not in a wash-up meeting once everything is finished.

Skipping the threat profile. A generic list of MITRE ATT&CK techniques, borrowed from another client’s engagement, tests less relevant ground. A list built around your actual sector works harder, whether that means business email compromise for a professional services firm or point-of-sale malware for a retailer.

No one owning the fixes afterwards. The exercise itself is only half the value. Someone needs to actually implement the detection rules, alert thresholds and logging changes identified on the day. Otherwise the gaps get written down twice and closed never.

Running it once and stopping. Detection coverage decays as your infrastructure, staff and tooling change. A single exercise is a snapshot, not a standing guarantee that the same techniques will still be caught a year later.

Does your business need purple teaming, or a standard penetration test?

If you have never had an external test at all, start there. A straightforward penetration test or vulnerability assessment finds the open doors before anyone argues about how well your SOC would spot someone walking through them.

Purple teaming earns its keep once you already have monitoring in place. That could be an in-house SOC, a managed detection service, or an EDR platform someone is actually watching. At that point, the question worth paying for shifts. It moves from “can they get in” to “would we catch it.” A collaborative exercise answers that far more directly than a report written after the fact.

Aardwolf Security scopes penetration tests and red team engagements around exactly this kind of decision. We match the exercise to what a business is actually trying to learn, rather than defaulting to whichever test sounds most impressive. If you are weighing up which approach fits your setup, it is worth a conversation before you commission anything.

Frequently asked questions

Is purple teaming the same as a red team engagement?
No. A red team engagement is typically covert, testing whether an attack succeeds without your defenders’ knowledge. Purple teaming is deliberately transparent, with both sides collaborating throughout so the defensive team learns from every step.

How long does a purple team exercise take?
It depends on how many attacker techniques are in scope. Most engagements run from a few days to a couple of weeks. Each technique has to be executed, observed, tuned and re-tested before the team moves to the next one.

Do you need to run a red team test first?
Not necessarily. Some organisations run purple teaming first to build baseline detection coverage. They commission a covert red team later, to confirm those defences hold up under a genuinely blind test.

What does purple teaming cost compared with a penetration test?
Pricing depends heavily on scope and the number of techniques covered. Expect it to sit closer to a red team engagement than a standard vulnerability scan. It needs experienced people on both the offensive and defensive side for the full session.

What tools do purple teams use?
Most exercises are structured around the MITRE ATT&CK framework to select techniques. Alongside that sits whatever SIEM, EDR or logging platform the blue team already runs, so the test reflects real detection capability rather than a lab environment.