It refers to domains where only subdomains are active and the apex (root) domain does not serve any content or DNS response. This behavior is often used by threat actors to hide malicious activity within subdomains, making detection harder while keeping the main domain seemingly benign.
Three questions every analyst asks before acting on this signal.
It refers to domains where only subdomains are active and the apex (root) domain does not serve any content or DNS response. This behavior is often used by threat actors to hide malicious activity within subdomains, making detection harder while keeping the main domain seemingly benign.
Because legitimate domains typically maintain active root-level records for branding, mail, or redirection purposes. When only subdomains are active, it often indicates evasive infrastructure — such as phishing or C2 operations that leverage subdomain generation or dynamic DNS services.
By monitoring patterns where the root domain has no recent DNS resolution or HTTP response, while multiple subdomains remain active. Correlating this behavior with other indicators (like new SSL certificates or fast-flux subdomain patterns) strengthens malicious attribution.
A realistic shape of the entry the engine appends to the risk_signals array when this signal fires. Evidence keys are subgroup-default; per-signal overrides documented in the API reference.
{
"slug": "ip_only_serve_on_subdomain",
"name": "Subdomain-Only Active Domain",
"group": "dns_history",
"subgroup": "domain_lifecycle",
"direction": "malicious",
"evidence": {
"first_seen_days_ago": 4,
"activation_event": "newly_resolved",
"dormancy_days_before": 0,
"registered_days_ago": 7
}
}4 other signals share the same subgroup. They detect related behaviors and often co-fire on the same IOC.
It refers to a domain that previously maintained a clean reputation and was considered safe, but has later been repurpos…
It indicates that the domain has recently become active for the first time, either by starting to resolve in DNS or by r…
It indicates that one or more subdomains under a given domain have recently become active or resolvable in DNS. This pat…
It indicates that the domain has started resolving to a new IP address for the first time. This event often marks a chan…
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