Block Active Exfiltration Pathways

ContainmentP130 min
📤 Data Exfiltration🔒 Ransomware👤 Insider Threat
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Immediately block all identified exfiltration channels to stop ongoing data loss. Implement blocks at multiple layers (endpoint, proxy, firewall, DNS) to ensure no fallback path remains.

Actions

  1. 1.Block exfiltration destination IPs and domains on the perimeter firewall: add to deny list and verify with `show access-list` or equivalent. Confirm blocks are applied to all egress points.
  2. 2.Add exfiltration domains to the DNS sinkhole/blackhole: update the DNS resolver block list or RPZ zone. Verify resolution fails: `nslookup exfil-domain.com` should return NXDOMAIN or sinkhole IP.
  3. 3.Block cloud storage sync tools at the proxy level: create URL category blocks for file-sharing domains (mega.nz, rclone endpoints, transfer.sh). Apply SSL inspection to detect HTTPS-based exfiltration.
  4. 4.On the endpoint, use EDR application blocking to kill and prevent execution of rclone.exe, megasync.exe, and other identified exfil tools: CrowdStrike IOA exclusion or Defender ASR rule.
  5. 5.If DNS tunneling is suspected, restrict DNS to internal resolvers only and block direct outbound UDP/TCP 53 at the firewall: `iptables -A OUTPUT -p udp --dport 53 -j DROP` (except resolver IPs).

Queries

CommonSecurityLog | where TimeGenerated > ago(1h) | where DestinationIP in ("EXFIL_IP1","EXFIL_IP2") or DestinationHostName in ("exfil-domain.com") | summarize BlockedCount=count() by DeviceAction, SourceIP, DestinationIP | where DeviceAction == "blocked"
DnsEvents | where TimeGenerated > ago(1h) | where Name has "exfil-domain.com" | summarize QueryCount=count() by ClientIP, Name, QueryType | order by QueryCount desc
index=proxy action=denied dest_host IN ("mega.nz","transfer.sh","file.io","rclone.*") | stats count by src_ip, dest_host, action | sort -count

Notes

  • Implement blocks at multiple layers simultaneously -- attackers with active access will try fallback exfiltration methods within minutes of a single channel being blocked.
  • Monitor for new outbound connections from the staging host immediately after blocks are applied. The attacker may attempt to switch to a different exfiltration method.