Detect Web Service in Splunk
Adversaries may use an existing, legitimate external web service as a means for relaying data to/from a compromised system. Popular websites and cloud services such as Google Drive, OneDrive, Dropbox, Pastebin, GitHub, and Discord may act as C2 channels due to the high likelihood that hosts within a network already communicate with them. This provides cover in expected noise and takes advantage of SSL/TLS encryption offered by these providers. Use of web services also protects back-end C2 infrastructure from discovery through malware binary analysis while enabling operational resiliency through dynamic infrastructure changes.
MITRE ATT&CK
- Tactic
- Command and Control
- Technique
- T1102 Web Service
- Canonical reference
- https://attack.mitre.org/techniques/T1102/
SPL Detection Query
index=wineventlog sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode=3
| eval RemoteHostname=lower(DestinationHostname)
| where match(RemoteHostname, "(pastebin\.com|paste\.ee|ghostbin\.co|api\.github\.com|raw\.githubusercontent\.com|gist\.github\.com|graph\.microsoft\.com|onedrive\.live\.com|www\.googleapis\.com|drive\.google\.com|storage\.googleapis\.com|api\.dropboxapi\.com|content\.dropboxapi\.com|discord\.com|discordapp\.com|cdn\.discordapp\.com|api\.telegram\.org|firebaseio\.com|firebase\.googleapis\.com|gitee\.com|top4top\.io|api\.slack\.com)")
| eval ImageLower=lower(Image)
| where NOT match(ImageLower, "(chrome\.exe|firefox\.exe|msedge\.exe|iexplore\.exe|opera\.exe|brave\.exe|onedrive\.exe|googledrivesync\.exe|dropbox\.exe|slack\.exe|teams\.exe|discord\.exe)")
| eval SuspiciousProcess=if(match(ImageLower, "(powershell\.exe|pwsh\.exe|cmd\.exe|wscript\.exe|cscript\.exe|mshta\.exe|rundll32\.exe|regsvr32\.exe|certutil\.exe|bitsadmin\.exe|curl\.exe|wget\.exe)"), 1, 0)
| eval ScriptingProcess=if(match(ImageLower, "(python\.exe|python3\.exe|ruby\.exe|perl\.exe|node\.exe)"), 1, 0)
| eval OfficeParent=if(match(lower(ParentImage), "(winword\.exe|excel\.exe|powerpnt\.exe|outlook\.exe|acrobat\.exe|acrord32\.exe)"), 1, 0)
| eval RiskScore=SuspiciousProcess*3 + ScriptingProcess*2 + OfficeParent*4
| where RiskScore > 0
| table _time, host, User, Image, CommandLine, ParentImage, ParentCommandLine, DestinationHostname, DestinationIp, DestinationPort, SuspiciousProcess, ScriptingProcess, OfficeParent, RiskScore
| sort - RiskScore, - _timeDetects non-browser processes connecting to known web service platforms abused for C2 using Sysmon Event ID 3 (Network Connection). Excludes known legitimate applications and cloud sync clients. Assigns a risk score based on the initiating process type: office applications spawning web service connections score highest (4 points, indicating drive-by exploitation), LOLBins and scripting engines score 3 and 2 respectively. High-risk-score events should be immediately investigated for C2 infrastructure or payload staging.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Legitimate developer tools or CI/CD pipelines making API calls to GitHub, Firebase, or Google APIs
- IT management tools and monitoring agents that poll cloud APIs for configuration or telemetry upload
- Custom line-of-business applications built on cloud storage APIs
- PowerShell scripts used legitimately by administrators to upload logs or reports to cloud storage
- Antivirus or endpoint agents uploading telemetry to cloud-hosted collection endpoints
Other platforms for T1102
Testing Methodology
Validate this detection against 5 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1PowerShell Dead Drop Resolver via Pastebin
Expected signal: Sysmon Event ID 1: Process Create with Image=powershell.exe, CommandLine containing 'Net.WebClient' and 'pastebin.com'. Sysmon Event ID 3: Network Connection to pastebin.com on port 443. Sysmon Event ID 22: DNS query for pastebin.com. PowerShell ScriptBlock Log Event ID 4104 with the full command.
- Test 2Simulated OneDrive C2 Channel via Microsoft Graph API
Expected signal: Sysmon Event ID 1: Process Create with Image=powershell.exe, CommandLine containing 'Invoke-RestMethod' and 'graph.microsoft.com'. Sysmon Event ID 3: Network Connection to graph.microsoft.com on port 443. Sysmon Event ID 22: DNS query for graph.microsoft.com.
- Test 3Curl-based GitHub Raw Content Retrieval (Linux/macOS)
Expected signal: Syslog/auditd: execve syscall for curl with arguments containing raw.githubusercontent.com. Network connection to 185.199.x.x (GitHub CDN) on port 443. Linux audit log: SYSCALL record with comm=curl, SOCKADDR with dest IP. File creation at /tmp/df00tech-test-payload.txt.
- Test 4Discord Webhook C2 Simulation
Expected signal: Sysmon Event ID 1: Process Create with Image=powershell.exe, CommandLine containing 'discord.com' and 'Invoke-RestMethod'. Sysmon Event ID 3: Network Connection to discord.com port 443. Sysmon Event ID 22: DNS query for discord.com. The request will fail with HTTP 401/404 but the network telemetry will still be generated.
- Test 5Python-based Telegram Bot API C2 Simulation
Expected signal: Sysmon Event ID 1: Process Create with Image=python.exe, CommandLine containing 'api.telegram.org'. Sysmon Event ID 3: Network Connection to api.telegram.org port 443. Sysmon Event ID 22: DNS query for api.telegram.org. The request will return HTTP 401 (invalid token) but network telemetry is generated.
References (10)
- https://attack.mitre.org/techniques/T1102/
- https://www.broadcom.com/support/security-center/protection-bulletin/birdyclient-malware-leverages-microsoft-graph-api-for-c-c-communication
- https://www.welivesecurity.com/en/eset-research/evasivepanda-apt-group-uses-update-channels-of-legitimate-applications-for-cyberespionage/
- https://symantec-enterprise-blogs.security.com/threat-intelligence/daggerfly-apt-actor-macos
- https://unit42.paloaltonetworks.com/latrodectus-cybercrime-affiliate-activity/
- https://www.microsoft.com/en-us/security/blog/2021/05/28/breaking-down-nobelium-latest-early-stage-toolset/
- https://www.cybereason.com/blog/molerats-in-the-cloud-new-malware-arsenal-abuses-cloud-platforms-in-middle-east-espionage-campaign
- https://blog.talosintelligence.com/2018/08/rocke-champion-of-monero-miners.html
- https://hp.com/h20195/v2/getpdf.aspx/a00127091enw.pdf
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1102/T1102.md
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