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Upgrade to ProDetect Ransomware-Affiliate Custom Exfiltration Tooling (StealBit & Exmatter) in Sumo Logic CSE
Ransomware affiliates increasingly deploy purpose-built exfiltration utilities instead of general-purpose tools like rclone, separating the data-theft channel from the encryption payload's C2 infrastructure. StealBit, distributed by LockBit affiliates, is a standalone binary (originally HTTP/HTTPS-based, later versions moved to a raw multi-threaded TCP protocol) that is dropped with a randomized hex/GUID filename into ProgramData, AppData\Local\Temp, or Users\Public, then run with no command-line arguments. It enumerates local and mapped drives, filters for high-value file types (databases, documents, spreadsheets, credential stores), and spawns dozens of concurrent upload threads to a single hardcoded external host to maximize throughput before the encryptor executes. Exmatter, used by BlackMatter/Noberus, BlackCat/ALPHV, and BlackByte affiliates, is a .NET utility that prioritizes specific extensions (.sql, .mdf, .bak, .pdf, .doc/x, .xls/x, .rdp, .kdbx) and exfiltrates over SFTP, FTPS, or WebDAV to attacker-controlled infrastructure using credentials embedded in its configuration; several observed samples overwrite or truncate a subset of already-uploaded source files with random data immediately after a successful transfer, an anti-recovery and extra-leverage behavior distinct from the ransomware's own encryption routine. Both tools are typically staged and executed in the hours immediately preceding encryption, making the exfiltration phase a high-value, narrow detection window before impact.
MITRE ATT&CK
- Tactic
- Exfiltration
Sumo Detection Query
(_sourceCategory="windows/sysmon" OR _sourceCategory="endpoint/windows/sysmon") EventCode=1
(Image matches "*\\ProgramData\\*" OR Image matches "*\\AppData\\Local\\Temp\\*" OR Image matches "*\\Users\\Public\\*")
CommandLine=""
| where Image matches "*[0-9a-fA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F]*.exe"
| eval Signal="SuspiciousLoaderExec", RiskScore=75
| fields _messagetime, ComputerName, User, Image, CommandLine, Signal, RiskScore
| union (
(_sourceCategory="windows/sysmon" OR _sourceCategory="endpoint/windows/sysmon") EventCode=3
(DestinationPort=443 OR DestinationPort=21 OR DestinationPort=990 OR DestinationPort=22)
| timeslice 10m
| count AS ConnectionCount BY ComputerName, User, Image, DestinationIp, DestinationPort, _timeslice
| where ConnectionCount>=20
| eval Signal="HighFanoutExfilConnections", RiskScore=85
| fields _timeslice, ComputerName, User, Image, DestinationIp, DestinationPort, ConnectionCount, Signal, RiskScore
)
| sort by RiskScore descSumo Logic search combining Sysmon process creation (EventCode=1) for randomly-named, argument-less loaders dropped in common staging directories with Sysmon network connection (EventCode=3) events showing high fan-out to a single destination on FTPS/SFTP/HTTPS ports within a 10-minute timeslice, matching the StealBit/Exmatter exfiltration pattern.
Data Sources
Required Tables
False Positives & Tuning
- Installer temp binaries that momentarily match the random-name pattern but show no subsequent network fan-out — suppress by requiring correlation with the HighFanoutExfilConnections signal before alerting
- Backup jobs producing regular connection bursts to a known offsite IP — maintain a Sumo Logic lookup table of authorized backup destination IPs and exclude matches from DestinationIp
Other platforms for THREAT-Ransomware-AffiliateExfilTooling
Testing Methodology
Validate this detection against 2 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 1Simulate StealBit-Style Multi-Threaded Exfil Fan-Out
Expected signal: Sysmon Event ID 1 for a randomly-named executable created in ProgramData; Sysmon Event ID 3 showing 20+ outbound connections to the test endpoint on port 443 within a short window.
- Test 2Simulate Exmatter-Style Staging and Post-Upload File Corruption
Expected signal: Sysmon Event ID 11 for 60 file creations matching the .pdf extension within a short window; Sysmon Event ID 3 for the outbound SFTP connection on port 22; a second Event ID 11/2 for the modification of staged_1.pdf within minutes of the SFTP connection.
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