I received a lot of DMs after D2D and interview post, and one of the thing was Detection Engineering. I am trying to explain it in a very nutshell simple manner.
Detection engineering is basically the "ART" (notice the "") of writing rules that turn raw telemetry(let's say JSON) into an alert a human actually needs to look at. That's just it in one line.
The hard part isn't the concept, it's getting the rule specific enough(parameter wise, consider it as a broad variation of if-else statements) to catch real bad behavior without wasting your SOC in FPs.
On D2D the actual pipeline looks like:
Telemetry source (Sysmon, EDR agent, firewall logs)
↓
Log ingestion (Splunk, ELK, Sentinel, whatever SIEM)
↓
Detection rule (Sigma, KQL, SPL: the logic itself)
↓
Alert fires → analyst triages
An example could be suppose you want to detect a process masquerading as a legit binary, like malware naming itself svchost.exe but running from a weird path. Your telemetry source is Sysmon Event ID 1 (process creation). The field you actually care about is the image path versus the process name. A real svchost.exe runs from C:\Windows\System32. If Sysmon shows svchost.exe launching from AppData or Temp, that's your sign/signal.
A basic Sigma rule for that logic looks roughly like:
detection:
selection:
Image|endswith: '\svchost.exe'
Image|contains:
- '\AppData\'
- '\Temp\'
condition: selection
That's the whole idea. You're not detecting malware. You're detecting a specific, narrow behavior that legit software/process almost never does, so when it gets detected/fires/alert generated, it's actually worth an analyst's time and efforts.
The skill that separates a good detection engineer from someone who just copies rules off GitHub is knowing which fields actually matter for a given technique, and tuning out all the noise before it ever reaches the SOC queue. That tuning is 80% of the actual job. Writing the rule is the easy 20%.
If you're starting out, the best exercise is picking one MITRE ATT&CK technique, generating it yourself in a lab (Atomic Red Team is good for this), capturing the Sysmon/EDR telemetry it produces, and writing your own rule against real data instead of just reading someone else's.
What technique are you trying to build detection for right now? Happy to help work through the telemetry logic if you're stuck on it.
