--- name: detecting-ransomware-precursors-in-network-29925505b829 description: 'Detects early-stage ransomware indicators in network traffic before encryption begins, including initial access broker activity, command-and-control beaconing, credential harvesting, reconnaissance scanning, and staging behavior. Uses network detection tools (Zeek, Suricata, Arkime), SIEM correlation rules, and threat intelligence feeds to identify ransomware precursor patterns such as Cobalt Strike beacons, Mimikatz network signatures, and RDP brute-force attempts. Activates for requests involving pre-ransomware detection, network-based ransomware indicators, or early warning ransomware monitoring. ' domain: cybersecurity subdomain: ransomware-defense tags: - ransomware - detection - network-security - incident-response - defense version: 1.0.0 author: mahipal license: Apache-2.0 nist_csf: - PR.DS-11 - RS.MA-01 - RC.RP-01 - PR.IR-01 mitre_attack: - T1078 - T1190 - T1059 - T1003 - T1110 mitre_f3: version: '1.1' tactics: - initial-access - positioning - monetization techniques: - id: T1110 name: Brute Force tactic: initial-access source: attack - id: T1219 name: Remote Access Tools tactic: positioning source: attack - id: T1650 name: Acquire Access tactic: resource-development source: attack - id: F1018 name: Convert to Cryptocurrency tactic: monetization source: f3 --- # Detecting Ransomware Precursors in Network Traffic ## When to Use - Building detection rules for pre-ransomware network activity (the average time from Cobalt Strike deployment to encryption is 17 minutes) - Monitoring for initial access broker (IAB) indicators that precede ransomware deployment - Creating SIEM correlation rules that chain multiple precursor events into high-confidence alerts - Tuning network detection systems to distinguish ransomware staging from normal administrative activity - Investigating suspicious network patterns that may indicate ransomware operators have established a foothold **Do not use** for post-encryption response (see recovering-from-ransomware-attack). This skill focuses on the pre-encryption detection window where containment can prevent data loss. ## Prerequisites - Network detection platform (Zeek/Bro, Suricata, or Arkime/Moloch) deployed on network TAP or SPAN ports - SIEM platform (Splunk, Elastic Security, Microsoft Sentinel, or QRadar) ingesting network logs - Threat intelligence feeds covering ransomware IOCs (CISA, abuse.ch, OTX, MISP) - Network flow data (NetFlow/IPFIX) from core routers and firewalls - DNS query logging from internal resolvers - Full packet capture capability for incident investigation ## Workflow ### Step 1: Identify Ransomware Kill Chain Phases in Network Traffic Map network-observable indicators to each pre-encryption phase: | Kill Chain Phase | Network Indicators | Detection Source | |------------------|--------------------|------------------| | Initial Access | RDP brute force, VPN credential stuffing, phishing callback | Firewall logs, IDS, proxy logs | | C2 Establishment | Cobalt Strike beacons (HTTPS/DNS), Sliver/Brute Ratel callbacks | Zeek SSL/HTTP logs, DNS logs | | Credential Harvesting | NTLM relay, Kerberoasting, DCSync traffic | Zeek Kerberos/NTLM logs, DC logs | | Reconnaissance | Internal port scanning, AD enumeration (LDAP/SMB) | Zeek conn.log, flow data | | Lateral Movement | PsExec/WMI/WinRM traffic, RDP pivoting, SMB file copies | Zeek SMB/DCE-RPC logs | | Staging | Data aggregation, archive creation, cloud upload prep | Proxy logs, DNS logs, DLP | ### Step 2: Deploy Network Detection Rules **Suricata rules for common ransomware precursors:** ```yaml # Cobalt Strike default HTTPS beacon profile detection alert tls $HOME_NET any -> $EXTERNAL_NET any (msg:"RANSOMWARE PRECURSOR - Cobalt Strike Default TLS Certificate"; tls.cert_subject; content:"Major Cobalt Strike"; sid:3000001; rev:1;) # Cobalt Strike DNS beacon alert dns $HOME_NET any -> any 53 (msg:"RANSOMWARE PRECURSOR - Cobalt Strike DNS Beacon Pattern"; dns.query; pcre:"/^[a-z0-9]{3}\.[a-z]{4,8}\./"; threshold:type both, track by_src, count 50, seconds 60; sid:3000002; rev:1;) # Mimikatz network signature (DCSync - DRS GetNCChanges) alert tcp $HOME_NET any -> $HOME_NET 135 (msg:"RANSOMWARE PRECURSOR - Possible DCSync/Mimikatz"; content:"|05 00 0b|"; offset:0; depth:3; content:"|e3 51 4d 2b 4b 47 15 d2|"; sid:3000003; rev:1;) # Internal network scanning (many connections, few bytes) alert tcp $HOME_NET any -> $HOME_NET any (msg:"RANSOMWARE PRECURSOR - Internal Port Scan"; flags:S; threshold:type both, track by_src, count 100, seconds 10; sid:3000004; rev:1;) # PsExec service installation over SMB alert tcp $HOME_NET any -> $HOME_NET 445 (msg:"RANSOMWARE PRECURSOR - PsExec Service Install"; content:"|ff|SMB"; content:"PSEXESVC"; nocase; sid:3000005; rev:1;) # RDP brute force from internal host (lateral movement) alert tcp $HOME_NET any -> $HOME_NET 3389 (msg:"RANSOMWARE PRECURSOR - Internal RDP Brute Force"; flow:to_server,established; threshold:type both, track by_src, count 20, seconds 60; sid:3000006; rev:1;) # Large SMB file transfer (data staging) alert tcp $HOME_NET any -> $HOME_NET 445 (msg:"RANSOMWARE PRECURSOR - Large SMB Transfer Possible Staging"; flow:to_server,established; dsize:>60000; threshold:type both, track by_src, count 100, seconds 300; sid:3000007; rev:1;) ``` **Zeek scripts for behavioral detection:** ```zeek # detect_ransomware_precursors.zeek # Detect high volume of failed SMB connections (credential testing) @load base/protocols/smb module RansomwarePrecursor; export { redef enum Notice::Type += { SMB_Brute_Force, Suspicious_Internal_Scan, Excessive_DNS_Queries, SMB_Admin_Share_Access, }; const smb_fail_threshold = 10 &redef; const scan_threshold = 50 &redef; const dns_query_threshold = 200 &redef; } global smb_fail_count: table[addr] of count &default=0 &create_expire=5min; global conn_count: table[addr] of set[addr] &create_expire=1min; event smb2_message(c: connection, hdr: SMB2::Header, is_orig: bool) { if (hdr$status != 0) { ++smb_fail_count[c$id$orig_h]; if (smb_fail_count[c$id$orig_h] >= smb_fail_threshold) { NOTICE([$note=SMB_Brute_Force, $msg=fmt("Host %s has %d failed SMB attempts", c$id$orig_h, smb_fail_count[c$id$orig_h]), $src=c$id$orig_h, $identifier=cat(c$id$orig_h)]); } } } event new_connection(c: connection) { if (c$id$orig_h in Site::local_nets && c$id$resp_h in Site::local_nets) { if (c$id$orig_h !in conn_count) conn_count[c$id$orig_h] = set(); add conn_count[c$id$orig_h][c$id$resp_h]; if (|conn_count[c$id$orig_h]| >= scan_threshold) { NOTICE([$note=Suspicious_Internal_Scan, $msg=fmt("Host %s connected to %d internal hosts in 1 min", c$id$orig_h, |conn_count[c$id$orig_h]|), $src=c$id$orig_h, $identifier=cat(c$id$orig_h)]); } } } ``` ### Step 3: Create SIEM Correlation Rules **Splunk correlation for ransomware precursor chain:** ```spl | tstats count FROM datamodel=Network_Traffic WHERE earliest=-24h All_Traffic.dest_port IN (445, 135, 139, 3389, 5985, 5986) AND All_Traffic.src_ip IN 10.0.0.0/8 AND All_Traffic.dest_ip IN 10.0.0.0/8 BY All_Traffic.src_ip, All_Traffic.dest_port, _time span=1h | stats dc(All_Traffic.dest_port) as port_count, values(All_Traffic.dest_port) as ports, count as total_conns BY All_Traffic.src_ip | where port_count >= 3 AND total_conns > 50 | rename All_Traffic.src_ip as src_ip | lookup threat_intel_ioc ip as src_ip OUTPUT threat_type | eval risk_score = case( port_count >= 5 AND total_conns > 200, "CRITICAL", port_count >= 3 AND total_conns > 50, "HIGH", 1=1, "MEDIUM") | table src_ip, ports, port_count, total_conns, risk_score, threat_type ``` **Microsoft Sentinel KQL - Ransomware precursor correlation:** ```kql let timeframe = 24h; let RDPBruteForce = SecurityEvent | where TimeGenerated > ago(timeframe) | where EventID == 4625 | where LogonType == 10 | summarize FailedRDP = count() by TargetAccount, IpAddress, bin(TimeGenerated, 1h) | where FailedRDP > 10; let SuspiciousSMB = SecurityEvent | where TimeGenerated > ago(timeframe) | where EventID == 5145 | where ShareName has "ADMIN$" or ShareName has "C$" or ShareName has "IPC$" | summarize AdminShareAccess = count() by SubjectUserName, IpAddress, bin(TimeGenerated, 1h) | where AdminShareAccess > 5; let ServiceInstalls = SecurityEvent | where TimeGenerated > ago(timeframe) | where EventID == 7045 | where ServiceName has_any ("PSEXESVC", "meterpreter", "beacon"); RDPBruteForce | join kind=inner SuspiciousSMB on IpAddress | project TimeGenerated, IpAddress, TargetAccount, FailedRDP, SubjectUserName, AdminShareAccess | extend AlertTitle = "Ransomware Precursor: RDP Brute Force + Admin Share Access" ``` ### Step 4: Integrate Threat Intelligence Configure automated IOC feeds for known ransomware infrastructure: ```bash # Download and update ransomware C2 blocklists # abuse.ch Feodo Tracker (Cobalt Strike, TrickBot, BazarLoader C2s) curl -s https://feodotracker.abuse.ch/downloads/ipblocklist.csv | \ grep -v "^#" | cut -d, -f2 > /opt/threat-intel/feodo_ips.txt # abuse.ch URLhaus (malware distribution URLs) curl -s https://urlhaus.abuse.ch/downloads/csv_recent/ | \ grep -v "^#" | cut -d, -f3 > /opt/threat-intel/urlhaus_urls.txt # abuse.ch ThreatFox (ransomware IOCs) curl -s https://threatfox.abuse.ch/export/csv/recent/ | \ grep -i "ransomware" | cut -d, -f3 > /opt/threat-intel/ransomware_iocs.txt # CISA Known Exploited Vulnerabilities (initial access vectors) curl -s https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json | \ python3 -c "import json,sys; data=json.load(sys.stdin); [print(v['cveID'],v['vendorProject'],v['product']) for v in data['vulnerabilities'] if 'ransomware' in v.get('knownRansomwareCampaignUse','').lower()]" ``` ### Step 5: Establish Alert Triage and Escalation Define triage procedures based on precursor confidence level: | Alert Type | Confidence | Response Time | Action | |------------|-----------|---------------|--------| | Confirmed Cobalt Strike beacon | High | 15 minutes | Isolate host immediately, trigger IR | | DCSync/Kerberoasting from non-DC | High | 15 minutes | Disable account, isolate host, trigger IR | | Internal port scan + admin share access | Medium-High | 30 minutes | Investigate source host, check EDR telemetry | | RDP brute force from internal host | Medium | 1 hour | Verify if legitimate admin activity, check host | | Unusual DNS query volume | Low-Medium | 4 hours | Check for DNS tunneling, correlate with other alerts | ## Key Concepts | Term | Definition | |------|------------| | **Ransomware Precursor** | Network activity that precedes ransomware encryption, including C2 communication, lateral movement, and data staging | | **Dwell Time** | Time between initial compromise and ransomware deployment, averaging 21 days but sometimes as short as 17 minutes | | **Initial Access Broker (IAB)** | Threat actors who sell compromised network access to ransomware operators on dark web markets | | **Beaconing** | Periodic C2 callbacks from implants (Cobalt Strike, Sliver) that can be detected by analyzing connection timing patterns | | **Kerberoasting** | Credential harvesting technique requesting Kerberos service tickets for offline cracking, detectable via unusual TGS-REQ patterns | | **DCSync** | Technique using Directory Replication Service to extract password hashes from domain controllers, critical ransomware precursor | ## Tools & Systems - **Zeek (formerly Bro)**: Network analysis framework generating structured logs for SMB, Kerberos, DNS, HTTP, and TLS connections - **Suricata**: High-performance IDS/IPS with protocol analysis and multi-threading support for ransomware signature detection - **Arkime (formerly Moloch)**: Full packet capture and search platform for deep forensic investigation of network events - **RITA (Real Intelligence Threat Analytics)**: Open-source tool for detecting beaconing, DNS tunneling, and long connections in Zeek logs - **AC-Hunter**: Network threat hunting platform from Active Countermeasures for beacon detection and C2 identification ## Common Scenarios ### Scenario: Detecting LockBit Precursors in a Manufacturing Network **Context**: A manufacturing company's SOC receives an alert for unusual SMB traffic from a workstation (10.1.5.42) in the engineering department. The workstation connected to 47 internal hosts on port 445 within 5 minutes at 2:00 AM. **Approach**: 1. Zeek conn.log analysis shows 10.1.5.42 initiated connections to 47 unique internal IPs on port 445, 135, and 3389 between 01:55-02:05 2. Zeek ssl.log reveals an outbound HTTPS connection to 185.x.x.x every 60 seconds with consistent 48-byte payloads (Cobalt Strike beacon pattern) 3. RITA beacon analysis confirms high beacon score (0.96) for the external IP with 60-second jitter 4. Zeek kerberos.log shows TGS-REQ for multiple SPN accounts from 10.1.5.42 (Kerberoasting) 5. SMB tree_connect events show access to ADMIN$ shares on 12 hosts (lateral movement staging) 6. Containment: Host isolated, credentials for engineering user reset, blocking rule for C2 IP deployed 7. Full IR initiated before ransomware deployment could begin **Pitfalls**: - Dismissing internal port scans as vulnerability scanner activity without verifying the source is an authorized scanner - Not correlating individual low-severity alerts (DNS anomaly + SMB access + failed logins) into a high-severity chain - Setting detection thresholds too high to avoid false positives, missing low-and-slow reconnaissance - Ignoring encrypted traffic analysis (JA3/JA4 fingerprinting) that can identify Cobalt Strike even in TLS tunnels ## Output Format ``` ## Ransomware Precursor Detection Alert **Alert ID**: [SIEM-generated ID] **Detection Time**: [Timestamp] **Source Host**: [IP / Hostname] **Confidence**: [High / Medium / Low] **Kill Chain Phase**: [Initial Access / C2 / Credential Harvest / Recon / Lateral Movement / Staging] ### Indicators Detected | Indicator | Source | Detail | MITRE ATT&CK | |-----------|--------|--------|--------------| | [Type] | [Zeek/Suricata/SIEM] | [Description] | [T-ID] | ### Correlation Chain 1. [Timestamp] - [Event 1] 2. [Timestamp] - [Event 2] 3. [Timestamp] - [Event 3] ### Recommended Actions - [ ] Isolate source host from network - [ ] Check EDR telemetry for host-based indicators - [ ] Reset credentials for affected user accounts - [ ] Block identified C2 infrastructure - [ ] Escalate to incident response team ``` --- Source attribution: costrict-plugins-repo Original project: https://github.com/costrict-plugins-repo/mukul975-anthropic-cybersecurity-skills-cybersecurity-skills/blob/1b344d155f00bae5cf27d8eba9508e8f5050d904/skills/detecting-ransomware-precursors-in-network/SKILL.md License: Apache-2.0 License information: https://www.apache.org/licenses/LICENSE-2.0 Original upstream instructions; downloaded from Mega AI Hub. ## Upstream license notice Apache License Version 2.0, January 2004 http://www.apache.org/licenses/ TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 1. Definitions. "License" shall mean the terms and conditions for use, reproduction, and distribution as defined by Sections 1 through 9 of this document. "Licensor" shall mean the copyright owner or entity authorized by the copyright owner that is granting the License. "Legal Entity" shall mean the union of the acting entity and all other entities that control, are controlled by, or are under common control with that entity. For the purposes of this definition, "control" means (i) the power, direct or indirect, to cause the direction or management of such entity, whether by contract or otherwise, or (ii) ownership of fifty percent (50%) or more of the outstanding shares, or (iii) beneficial ownership of such entity. "You" (or "Your") shall mean an individual or Legal Entity exercising permissions granted by this License. "Source" form shall mean the preferred form for making modifications, including but not limited to software source code, documentation source, and configuration files. "Object" form shall mean any form resulting from mechanical transformation or translation of a Source form, including but not limited to compiled object code, generated documentation, and conversions to other media types. "Work" shall mean the work of authorship, whether in Source or Object form, made available under the License, as indicated by a copyright notice that is included in or attached to the work (an example is provided in the Appendix below). "Derivative Works" shall mean any work, whether in Source or Object form, that is based on (or derived from) the Work and for which the editorial revisions, annotations, elaborations, or other modifications represent, as a whole, an original work of authorship. For the purposes of this License, Derivative Works shall not include works that remain separable from, or merely link (or bind by name) to the interfaces of, the Work and Derivative Works thereof. "Contribution" shall mean any work of authorship, including the original version of the Work and any modifications or additions to that Work or Derivative Works thereof, that is intentionally submitted to the Licensor for inclusion in the Work by the copyright owner or by an individual or Legal Entity authorized to submit on behalf of the copyright owner. For the purposes of this definition, "submitted" means any form of electronic, verbal, or written communication sent to the Licensor or its representatives, including but not limited to communication on electronic mailing lists, source code control systems, and issue tracking systems that are managed by, or on behalf of, the Licensor for the purpose of discussing and improving the Work, but excluding communication that is conspicuously marked or otherwise designated in writing by the copyright owner as "Not a Contribution." "Contributor" shall mean Licensor and any individual or Legal Entity on behalf of whom a Contribution has been received by the Licensor and subsequently incorporated within the Work. 2. Grant of Copyright License. Subject to the terms and conditions of this License, each Contributor hereby grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare Derivative Works of, publicly display, publicly perform, sublicense, and distribute the Work and such Derivative Works in Source or Object form. 3. Grant of Patent License. Subject to the terms and conditions of this License, each Contributor hereby grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable (except as stated in this section) patent license to make, have made, use, offer to sell, sell, import, and otherwise transfer the Work, where such license applies only to those patent claims licensable by such Contributor that are necessarily infringed by their Contribution(s) alone or by combination of their Contribution(s) with the Work to which such Contribution(s) was submitted. If You institute patent litigation against any entity (including a cross-claim or counterclaim in a lawsuit) alleging that the Work or a Contribution incorporated within the Work constitutes direct or contributory patent infringement, then any patent licenses granted to You under this License for that Work shall terminate as of the date such litigation is filed. 4. Redistribution. You may reproduce and distribute copies of the Work or Derivative Works thereof in any medium, with or without modifications, and in Source or Object form, provided that You meet the following conditions: (a) You must give any other recipients of the Work or Derivative Works a copy of this License; and (b) You must cause any modified files to carry prominent notices stating that You changed the files; and (c) You must retain, in the Source form of any Derivative Works that You distribute, all copyright, patent, trademark, and attribution notices from the Source form of the Work, excluding those notices that do not pertain to any part of the Derivative Works; and (d) If the Work includes a "NOTICE" text file as part of its distribution, then any Derivative Works that You distribute must include a readable copy of the attribution notices contained within such NOTICE file, excluding any notices that do not pertain to any part of the Derivative Works, in at least one of the following places: within a NOTICE text file distributed as part of the Derivative Works; within the Source form or documentation, if provided along with the Derivative Works; or, within a display generated by the Derivative Works, if and wherever such third-party notices normally appear. The contents of the NOTICE file are for informational purposes only and do not modify the License. You may add Your own attribution notices within Derivative Works that You distribute, alongside or as an addendum to the NOTICE text from the Work, provided that such additional attribution notices cannot be construed as modifying the License. You may add Your own copyright statement to Your modifications and may provide additional or different license terms and conditions for use, reproduction, or distribution of Your modifications, or for any such Derivative Works as a whole, provided Your use, reproduction, and distribution of the Work otherwise complies with the conditions stated in this License. 5. Submission of Contributions. Unless You explicitly state otherwise, any Contribution intentionally submitted for inclusion in the Work by You to the Licensor shall be under the terms and conditions of this License, without any additional terms or conditions. Notwithstanding the above, nothing herein shall supersede or modify the terms of any separate license agreement you may have executed with Licensor regarding such Contributions. 6. Trademarks. This License does not grant permission to use the trade names, trademarks, service marks, or product names of the Licensor, except as required for reasonable and customary use in describing the origin of the Work and reproducing the content of the NOTICE file. 7. Disclaimer of Warranty. Unless required by applicable law or agreed to in writing, Licensor provides the Work (and each Contributor provides its Contributions) on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. You are solely responsible for determining the appropriateness of using or redistributing the Work and assume any risks associated with Your exercise of permissions under this License. 8. Limitation of Liability. In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall any Contributor be liable to You for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising as a result of this License or out of the use or inability to use the Work (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if such Contributor has been advised of the possibility of such damages. 9. Accepting Warranty or Additional Liability. While redistributing the Work or Derivative Works thereof, You may choose to offer, and charge a fee for, acceptance of support, warranty, indemnity, or other liability obligations and/or rights consistent with this License. However, in accepting such obligations, You may act only on Your own behalf and on Your sole responsibility, not on behalf of any other Contributor, and only if You agree to indemnify, defend, and hold each Contributor harmless for any liability incurred by, or claims asserted against, such Contributor by reason of your accepting any such warranty or additional liability. END OF TERMS AND CONDITIONS APPENDIX: How to apply the Apache License to your work. To apply the Apache License to your work, attach the following boilerplate notice, with the fields enclosed by brackets "[]" replaced with your own identifying information. (Don't include the brackets!) The text should be enclosed in the appropriate comment syntax for the file format. Please do not remove or change the license header comment from a contributed file except when necessary. Copyright 2026 mukul975 Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. # Mega AI Hub resource metadata Creator / publisher: costrict-plugins-repo Original project: https://github.com/costrict-plugins-repo/mukul975-anthropic-cybersecurity-skills-cybersecurity-skills/blob/1b344d155f00bae5cf27d8eba9508e8f5050d904/skills/detecting-ransomware-precursors-in-network/SKILL.md Attribution basis: Source repository record Fields of work: Development & Engineering Roles: Security Engineer Specialties: Specialty not specified Tools: Arkime, Siem, Suricata, Zeek Country applicability: Country not specified Classification basis: Source catalog labels Instruction SHA-256: ee40d28ece0bef4d82095ab83fe53344d7f19cad33d5ca5f222823e588a9d249