An attacker signs in with a valid account. Using PowerShell and a remote management tool already approved on the network, they explore file servers and copy data out in small batches. The SIEM collects every log. The login succeeded, the tools are legitimate, and no single transfer crosses a threshold. No rule fires.<\/p>\n
The SIEM did not fail here. The logs were there. What was missing was detection logic that described this particular combination of actions. Collecting security data does not guarantee that every meaningful threat will be detected.<\/p>\n
That gap sits at the heart of rule-based SIEM limitations. A detection rule encodes a threat that someone already understood. When attackers introduce a new technique or change their behaviour, existing rules may not recognize it. A sound detection strategy therefore needs to cover both known attack patterns and suspicious behaviour that has not yet been documented.<\/p>\n