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45 changes: 45 additions & 0 deletions detection-rules/link_single_file_share_unkown_sender.yml
Original file line number Diff line number Diff line change
@@ -0,0 +1,45 @@
name: "Link: Single file sharing link with minimal content from unknown sender"
description: "Detects messages containing a single link to a free file hosting service with minimal body text from senders with limited history or recent contact patterns. The rule identifies potential malicious file sharing by analyzing link density, content brevity, and sender trust signals."
type: "rule"
severity: "high"
source: |
type.inbound
and length(body.current_thread.text) < 1000
and strings.icount(body.current_thread.text, "\n") < 20
// there are few links
and length(body.current_thread.links) < 10
// contains a link to free_file_host
and any(body.current_thread.links,
.href_url.domain.domain in $free_file_hosts
)
// is the only link to limewire
and length(filter(body.current_thread.links,
.href_url.domain.domain in $free_file_hosts
)
) == 1
and length(body.previous_threads) == 0
// negate highly trusted sender domains unless they fail DMARC authentication
and (
(
sender.email.domain.root_domain in $high_trust_sender_root_domains
and not headers.auth_summary.dmarc.pass
)
or sender.email.domain.root_domain not in $high_trust_sender_root_domains
)
and (
profile.by_sender_email().prevalence == "new"
or profile.by_sender_email().days_since.last_contact > 60
)
tags:
- "Attack surface reduction"
attack_types:
- "Malware/Ransomware"
- "Credential Phishing"
tactics_and_techniques:
- "Free file host"
- "Social engineering"
detection_methods:
- "Content analysis"
- "Sender analysis"
- "URL analysis"
id: "e560a504-23e3-5371-b71a-a8a694a359a6"
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