{ "hunt": { "meta": { "tlp": "clear", "hunt": { "handoff": "promote-to-detection", "trigger": "intel-report", "methodology": "model-assisted", "applicability": "campaign-specific", "justification": "Mallox ransomware affiliates target database infrastructure to maximize leverage for extortion. Detecting the PureCrypter loader's heavy anti-analysis logic and persistence allows intervention before the destructive encryption phase begins." }, "name": "PureCrypter evasion and Mallox ransomware execution", "type": "investigation", "labels": [ "hunt", "attack.t1497.001", "attack.t1562.001", "attack.t1129", "attack.t1547.001", "attack.t1486", "attack.t1047" ], "series": { "slug": "mallox-ransomware-affiliate-leverages-purecrypter-in-mssql-exploitation", "index": 2, "title": "Mallox ransomware affiliate leverages PureCrypter in MSSQL exploitation", "total": 2 }, "related": [ { "hunt": "mssql-bruteforce-and-exploitation", "reason": "This hunt picks up after the exploitation of the SQL server to deploy the loader.", "relation": "follows" }, { "hunt": "mallox-mssql-exploitation-initial-delivery", "relation": "follows" } ], "targets": { "hunter": { "name": "Hunt agent", "agent": true }, "analyst": { "name": "Tier-2 analyst", "role": "analyst" }, "endpoint": { "name": "Endpoint telemetry (hb_ surfaces)", "category": "endpoint", "telemetry": [ "endpoint" ] } }, "analysis": "While static rules might alert on 'Ydxhjxwf.exe', they are easily bypassed. This hunt looks for the loader's immutable logic\u2014WMI hardware queries, specific sandbox-evasion usernames, and stack-counted rare binaries in profile paths\u2014correlating three distinct surfaces into one high-fidelity verdict.", "coverage": [ { "stage": "loader-evasion-and-anti-analysis", "steps": [ "purecrypter-evasion-checks", "defender-exclusion-tampering" ], "status": "covered" }, { "stage": "persistence-run-key", "steps": [ "run-key-persistence" ], "status": "covered" }, { "stage": "mallox-ransomware-execution", "steps": [ "rare-profile-binaries" ], "status": "covered" }, { "stage": "sql-brute-force-access", "reason": "Belongs to another part of the 'Mallox ransomware affiliate leverages PureCrypter in MSSQL exploitation' series.", "status": "out_of_scope" }, { "stage": "sql-server-exploitation", "reason": "Belongs to another part of the 'Mallox ransomware affiliate leverages PureCrypter in MSSQL exploitation' series.", "status": "out_of_scope" }, { "stage": "initial-payload-delivery", "reason": "Belongs to another part of the 'Mallox ransomware affiliate leverages PureCrypter in MSSQL exploitation' series.", "status": "out_of_scope" } ], "scenario": { "stages": [ { "name": "MS-SQL Brute Force", "slug": "sql-brute-force-access", "tactic": "initial-access", "techniques": [ "T1110", "T1190" ], "observables": [ "Brute-force attempts against 'sa' account", "Source IP address in AS208091 (XHost Internet Solution)", "Approximately 320 authentication attempts per minute", "Targeting MS-SQL port (1433)" ] }, { "name": "MS-SQL Feature Exploitation", "slug": "sql-server-exploitation", "tactic": "execution", "techniques": [ "T1059.003" ], "observables": [ "Enabling 'TRUSTWORTHY' database parameter", "Enabling 'clr enabled' parameter", "Creating assembly named 'shell' (SqlShell DLL)", "Creating stored procedure 'cmd_exec'", "Enabling 'xp_cmdshell' configuration", "Enabling 'Ole Automation Procedures'", "Use of 'sp_oacreate' to create 'wscript.shell' OLE object", "Application name 'vYMiFrYR' in SQL connection logs" ] }, { "name": "PowerShell Downloader and WMIC Execution", "slug": "initial-payload-delivery", "tactic": "execution", "techniques": [ "T1059.001", "T1047" ], "observables": [ "echo and redirect used to create PowerShell script", "PowerShell script saved to C:\\ProgramData", "WMIC used to execute downloaded binary", "Downloading multimedia-themed files (e.g., .mp4, .wav, .pdf) containing encrypted payloads" ] }, { "name": "PureCrypter Anti-Analysis and Evasion", "slug": "loader-evasion-and-anti-analysis", "tactic": "defense-evasion", "techniques": [ "T1497.001", "T1562.001", "T1129" ], "observables": [ "WMI query 'select * from Win32_BIOS' to check for VMWare, Virtual, AMI, or Xen", "WMI query 'select * from Win32_ComputerSystem' to check for Microsoft or VMWare", "Process search for 'SbieDll.dll'", "Monitor size check for 1440x900", "Username check for 'john', 'anna', or 'xxxxxxxx'", "Execution of 'ipconfig /renew' and 'ipconfig /release' for network testing", "Patching 'EtwEventWrite' and 'AmsiScanBuffer' in memory", "Adding Windows Defender exclusions via 'MpPreference -Exclusion'" ] }, { "name": "Registry Run Key Persistence", "slug": "persistence-run-key", "tactic": "persistence", "techniques": [ "T1547.001" ], "observables": [ "Registry key addition in 'Software\\Microsoft\\Windows\\CurrentVersion\\Run\\'" ] }, { "name": "Mallox Ransomware Execution", "slug": "mallox-ransomware-execution", "tactic": "impact", "techniques": [ "T1486" ], "observables": [ "Ransomware executable named 'Ydxhjxwf.exe' in %appdata%", "Reflective code loading of stage 2 DLL", "Elevation of process privileges with 'SeDebugPrivilege'" ] } ], "summary": "An affiliate of Mallox ransomware targets internet-facing MS-SQL servers using brute-force attacks against the 'sa' account. Upon gaining access, the attacker exploits SQL features such as CLR assemblies and xp_cmdshell to deliver PureCrypter, a .NET loader that employs extensive anti-analysis and evasion techniques before executing the final Mallox ransomware payload." }, "severity": "high", "rationale": "Focus on high-value assets running SQL Server. The software inventory scoping step narrows the hunt to these servers, but leaving the scope_hosts parameter empty allows for a fleet-wide search if lateral movement is suspected.", "guardrails": { "claims": "no_unsupported", "evidence": "citation_required", "telemetry": "untrusted", "missing_data": "not_benign" }, "hypothesis": "An intruder is executing the PureCrypter loader on a compromised SQL server, performing heavy environment checks and establishing user-profile persistence before deploying the Mallox ransomware payload.", "parameters": { "scope_hosts": { "type": "list[host]", "default": [], "description": "Optional list of hostnames to scope the hunt (e.g., confirmed MSSQL servers)." }, "lookback_days": { "type": "number", "default": "14", "description": "Days of history to examine." }, "mallox_filename": { "from": { "ref": "https://blog.sekoia.io/mallox-ransomware-affiliate-leverages-purecrypter-in-microsoft-sql-exploitation-campaigns/", "kind": "article", "observed": "2024-05-02" }, "type": "string", "default": "Ydxhjxwf.exe", "description": "The specific ransomware filename observed in the report." }, "malicious_usernames": { "from": { "ref": "https://blog.sekoia.io/mallox-ransomware-affiliate-leverages-purecrypter-in-microsoft-sql-exploitation-campaigns/", "kind": "article", "observed": "2024-05-02" }, "type": "list[string]", "default": [ "john", "anna", "xxxxxxxx" ], "description": "Usernames checked by PureCrypter as part of anti-analysis; finding these in activity may indicate an evasion attempt." } }, "provenance": { "authors": [ { "org": "huntbase.io", "name": "Huntbase hunt generation" } ], "generated": { "by": "huntbase-hunt-generation", "from": "https://blog.sekoia.io/mallox-ransomware-affiliate-leverages-purecrypter-in-microsoft-sql-exploitation-campaigns/", "gates": [ "dry-run", "lint", "critic" ], "model": "hb_google/gemini-3-flash-preview" } }, "references": [ { "url": "https://blog.sekoia.io/mallox-ransomware-affiliate-leverages-purecrypter-in-microsoft-sql-exploitation-campaigns/", "name": "Mallox ransomware affiliate leverages PureCrypter in MSSQL exploitation" } ], "blind_spots": [ { "id": "missing-script-telemetry", "risk": "PureCrypter commonly uses PowerShell, but if a variant uses a different interpreter without script block logging, the Defender exclusion step will be silent.", "stage": "loader-evasion-and-anti-analysis", "question": "Was the exclusion or payload download performed via an obfuscated VBScript or JScript?", "requires": "hb_script_activity for non-PowerShell interpreters" }, { "id": "reflective-loading-blindspot", "risk": "Since reflective loading occurs in memory, file activity will not capture the transition. We rely on process monitoring of the initial loader and the prevalence of the resulting process.", "stage": "mallox-ransomware-execution", "question": "Can we see the reflective loading of the stage 2 DLL or the final payload?", "requires": "hb_module_activity" } ] }, "name": "PureCrypter evasion and Mallox ransomware execution", "description": "This hunt focuses on the behavioral indicators of the PureCrypter loader and the Mallox ransomware it drops. It identifies unique defense evasion techniques, such as WMI-based BIOS and manufacturer checks, screen size validation, and network resets. It then corroborates these with registry-based persistence in user profile Run keys and stack-counts rare binaries running from AppData. This multi-surface approach ensures visibility even if the final ransomware filenames rotate." }, "nodes": [ { "id": "hypothesis", "type": "hypothesis", "label": "Hypothesis", "config": { "tags": [], "series": { "slug": "mallox-ransomware-affiliate-leverages-purecrypter-in-mssql-exploitation", "index": 2, "title": "Mallox ransomware affiliate leverages PureCrypter in MSSQL exploitation", "total": 2 }, "coverage": [ { "stage": "loader-evasion-and-anti-analysis", "steps": [ "purecrypter-evasion-checks", "defender-exclusion-tampering" ], "status": "covered" }, { "stage": "persistence-run-key", "steps": [ "run-key-persistence" ], "status": "covered" }, { "stage": "mallox-ransomware-execution", "steps": [ "rare-profile-binaries" ], "status": "covered" }, { "stage": "sql-brute-force-access", "reason": "Belongs to another part of the 'Mallox ransomware affiliate leverages PureCrypter in MSSQL exploitation' series.", "status": "out_of_scope" }, { "stage": "sql-server-exploitation", "reason": "Belongs to another part of the 'Mallox ransomware affiliate leverages PureCrypter in MSSQL exploitation' series.", "status": "out_of_scope" }, { "stage": "initial-payload-delivery", "reason": "Belongs to another part of the 'Mallox ransomware affiliate leverages PureCrypter in MSSQL exploitation' series.", "status": "out_of_scope" } ], "rationale": "An intruder is executing the PureCrypter loader on a compromised SQL server, performing heavy environment checks and establishing user-profile persistence before deploying the Mallox ransomware payload.", "blind_spots": [ { "id": "missing-script-telemetry", "risk": "PureCrypter commonly uses PowerShell, but if a variant uses a different interpreter without script block logging, the Defender exclusion step will be silent.", "stage": "loader-evasion-and-anti-analysis", "question": "Was the exclusion or payload download performed via an obfuscated VBScript or JScript?", "requires": "hb_script_activity for non-PowerShell interpreters" }, { "id": "reflective-loading-blindspot", "risk": "Since reflective loading occurs in memory, file activity will not capture the transition. We rely on process monitoring of the initial loader and the prevalence of the resulting process.", "stage": "mallox-ransomware-execution", "question": "Can we see the reflective loading of the stage 2 DLL or the final payload?", "requires": "hb_module_activity" } ], "scoping_notes": "Focus on high-value assets running SQL Server. The software inventory scoping step narrows the hunt to these servers, but leaving the scope_hosts parameter empty allows for a fleet-wide search if lateral movement is suspected.", "beyond_detection": "While static rules might alert on 'Ydxhjxwf.exe', they are easily bypassed. This hunt looks for the loader's immutable logic\u2014WMI hardware queries, specific sandbox-evasion usernames, and stack-counted rare binaries in profile paths\u2014correlating three distinct surfaces into one high-fidelity verdict." } }, { "id": "scope-mssql-servers", "type": "query", "label": "Identify candidate SQL servers", "config": { "dsl": "sqlite", "role": "scoping", "source": "endpoint", "content": "SELECT DISTINCT device_hostname FROM hb_software_inventory WHERE (LOWER(package_name) LIKE '%sql%server%' OR LOWER(vendor_name) LIKE '%microsoft%') AND asset_scope = 'endpoint'", "surface": "hb_software_inventory", "description": "Focus the hunt on hosts with Microsoft SQL Server installed, as they are the primary targets of this campaign.", "expected_signal": "A list of hostnames likely hosting SQL Server. If empty, the hunt runs across the full estate." }, "parents": [ { "id": "hypothesis" } ], "primitive_config": { "dsl": "sqlite", "role": "scoping", "label": "Identify candidate SQL servers", "reads": [ "device_hostname", "package_name", "vendor_name", "asset_scope" ], "source": "hb_software_inventory", "target": "endpoint", "content": "SELECT DISTINCT device_hostname FROM hb_software_inventory WHERE (LOWER(package_name) LIKE '%sql%server%' OR LOWER(vendor_name) LIKE '%microsoft%') AND asset_scope = 'endpoint'", "silence": "not_evidence_of_absence", "expected": "A list of hostnames likely hosting SQL Server. If empty, the hunt runs across the full estate.", "verified": "dry-run", "verified_at": "2026-09-17" } }, { "id": "purecrypter-evasion-checks", "type": "query", "label": "Anti-analysis behavior and WMI checks", "config": { "dsl": "sqlite", "role": "detection-candidate", "source": "endpoint", "content": "SELECT device_hostname, process_cmd_line, user_name, time FROM hb_process_activity WHERE ('{{scope_hosts}}' = '' OR instr(',' || '{{scope_hosts}}' || ',', ',' || device_hostname || ',') > 0) AND (LOWER(process_cmd_line) LIKE '%win32_bios%' OR LOWER(process_cmd_line) LIKE '%win32_computersystem%' OR instr(',' || '{{malicious_usernames}}' || ',', ',' || LOWER(user_name) || ',') > 0 OR LOWER(process_cmd_line) LIKE '%ipconfig%renew%' OR LOWER(process_cmd_line) LIKE '%ipconfig%release%') AND time >= datetime('now', '-{{lookback_days}} days')", "surface": "hb_process_activity", "description": "Find process execution matching the loader's environment checks (WMI for BIOS/System) and the specific usernames it exits for.", "expected_signal": "Processes querying hardware identifiers or matching a known sandbox username. Finding BIOS/System WMI queries paired with ipconfig resets is highly indicative." }, "parents": [ { "id": "scope-mssql-servers" } ], "primitive_config": { "dsl": "sqlite", "role": "detection-candidate", "label": "Anti-analysis behavior and WMI checks", "reads": [ "device_hostname", "process_cmd_line", "user_name", "time" ], "source": "hb_process_activity", "target": "endpoint", "content": "SELECT device_hostname, process_cmd_line, user_name, time FROM hb_process_activity WHERE ('{{scope_hosts}}' = '' OR instr(',' || '{{scope_hosts}}' || ',', ',' || device_hostname || ',') > 0) AND (LOWER(process_cmd_line) LIKE '%win32_bios%' OR LOWER(process_cmd_line) LIKE '%win32_computersystem%' OR instr(',' || '{{malicious_usernames}}' || ',', ',' || LOWER(user_name) || ',') > 0 OR LOWER(process_cmd_line) LIKE '%ipconfig%renew%' OR LOWER(process_cmd_line) LIKE '%ipconfig%release%') AND time >= datetime('now', '-{{lookback_days}} days')", "silence": "not_evidence_of_absence", "expected": "Processes querying hardware identifiers or matching a known sandbox username. Finding BIOS/System WMI queries paired with ipconfig resets is highly indicative.", "verified": "dry-run", "verified_at": "2026-09-17" } }, { "id": "run-key-persistence", "type": "query", "label": "Persistence in user Run key", "config": { "dsl": "sqlite", "role": "enrichment", "source": "endpoint", "content": "SELECT device_hostname, reg_target, reg_value_data, time FROM hb_registry_activity WHERE ('{{scope_hosts}}' = '' OR instr(',' || '{{scope_hosts}}' || ',', ',' || device_hostname || ',') > 0) AND LOWER(reg_target) LIKE '%software\\microsoft\\windows\\currentversion\\run%' AND (LOWER(reg_value_data) LIKE '%\\appdata\\local\\%' OR LOWER(reg_value_data) LIKE '%\\appdata\\roaming\\%') AND time >= datetime('now', '-{{lookback_days}} days')", "surface": "hb_registry_activity", "description": "Identify the registry entry established by the loader to ensure survival after reboots.", "expected_signal": "A Run key pointing to a binary in a user-writable path. Normal applications usually install to Program Files." }, "parents": [ { "id": "scope-mssql-servers" } ], "primitive_config": { "dsl": "sqlite", "role": "enrichment", "label": "Persistence in user Run key", "reads": [ "device_hostname", "reg_target", "reg_value_data", "time" ], "source": "hb_registry_activity", "target": "endpoint", "content": "SELECT device_hostname, reg_target, reg_value_data, time FROM hb_registry_activity WHERE ('{{scope_hosts}}' = '' OR instr(',' || '{{scope_hosts}}' || ',', ',' || device_hostname || ',') > 0) AND LOWER(reg_target) LIKE '%software\\microsoft\\windows\\currentversion\\run%' AND (LOWER(reg_value_data) LIKE '%\\appdata\\local\\%' OR LOWER(reg_value_data) LIKE '%\\appdata\\roaming\\%') AND time >= datetime('now', '-{{lookback_days}} days')", "silence": "not_evidence_of_absence", "expected": "A Run key pointing to a binary in a user-writable path. Normal applications usually install to Program Files.", "verified": "dry-run", "verified_at": "2026-09-17" } }, { "id": "defender-exclusion-tampering", "type": "query", "label": "Windows Defender exclusion activity", "config": { "dsl": "sqlite", "role": "enrichment", "source": "endpoint", "content": "SELECT device_hostname, script_content, actor_user_name, time FROM hb_script_activity WHERE ('{{scope_hosts}}' = '' OR instr(',' || '{{scope_hosts}}' || ',', ',' || device_hostname || ',') > 0) AND (LOWER(script_content) LIKE '%mppreference%' AND LOWER(script_content) LIKE '%-exclusion%') AND time >= datetime('now', '-{{lookback_days}} days')", "surface": "hb_script_activity", "description": "Find the PowerShell commands used to suppress Defender alerts for the ransomware binary.", "expected_signal": "Script blocks adding the loader or payload path to MpPreference exclusions." }, "parents": [ { "id": "scope-mssql-servers" } ], "primitive_config": { "dsl": "sqlite", "role": "enrichment", "label": "Windows Defender exclusion activity", "reads": [ "device_hostname", "script_content", "actor_user_name", "time" ], "source": "hb_script_activity", "target": "endpoint", "content": "SELECT device_hostname, script_content, actor_user_name, time FROM hb_script_activity WHERE ('{{scope_hosts}}' = '' OR instr(',' || '{{scope_hosts}}' || ',', ',' || device_hostname || ',') > 0) AND (LOWER(script_content) LIKE '%mppreference%' AND LOWER(script_content) LIKE '%-exclusion%') AND time >= datetime('now', '-{{lookback_days}} days')", "silence": "not_evidence_of_absence", "expected": "Script blocks adding the loader or payload path to MpPreference exclusions.", "verified": "dry-run", "verified_at": "2026-09-17" } }, { "id": "rare-profile-binaries", "type": "query", "label": "Rare executables in user profile paths", "config": { "dsl": "sqlite", "role": "baseline", "source": "endpoint", "content": "SELECT LOWER(process_path) as path, COUNT(DISTINCT device_hostname) as hosts, COUNT(*) as runs, MIN(time) as first_seen FROM hb_process_activity WHERE ('{{scope_hosts}}' = '' OR instr(',' || '{{scope_hosts}}' || ',', ',' || device_hostname || ',') > 0) AND (LOWER(process_name) = LOWER('{{mallox_filename}}') OR (LOWER(process_path) LIKE '%\\appdata\\%' AND LOWER(process_path) LIKE '%.exe')) AND time >= datetime('now', '-{{lookback_days}} days') GROUP BY 1 HAVING hosts <= 3 ORDER BY hosts ASC", "surface": "hb_process_activity", "description": "Stack-count processes running from AppData to highlight the Mallox binary against fleet background noise.", "expected_signal": "Binaries seen on only one or two hosts, specifically matching the reported Mallox filename or running from unusual AppData subdirectories." }, "parents": [ { "id": "scope-mssql-servers" } ], "primitive_config": { "dsl": "sqlite", "role": "baseline", "label": "Rare executables in user profile paths", "reads": [ "process_path", "device_hostname", "time", "process_name" ], "source": "hb_process_activity", "target": "endpoint", "content": "SELECT LOWER(process_path) as path, COUNT(DISTINCT device_hostname) as hosts, COUNT(*) as runs, MIN(time) as first_seen FROM hb_process_activity WHERE ('{{scope_hosts}}' = '' OR instr(',' || '{{scope_hosts}}' || ',', ',' || device_hostname || ',') > 0) AND (LOWER(process_name) = LOWER('{{mallox_filename}}') OR (LOWER(process_path) LIKE '%\\appdata\\%' AND LOWER(process_path) LIKE '%.exe')) AND time >= datetime('now', '-{{lookback_days}} days') GROUP BY 1 HAVING hosts <= 3 ORDER BY hosts ASC", "silence": "not_evidence_of_absence", "baseline": { "window": "{{lookback_days}}d", "compare": "first_seen" }, "expected": "Binaries seen on only one or two hosts, specifically matching the reported Mallox filename or running from unusual AppData subdirectories.", "verified": "dry-run", "prevalence": { "by": "device_hostname", "key": [ "process_path" ], "rare_below": 3 }, "verified_at": "2026-09-17" } }, { "id": "triage-agent", "type": "analytic", "label": "Triaging PureCrypter and Mallox presence", "config": { "cite": "required", "tools": [ "endpoint" ], "context": [ "purecrypter-evasion-checks", "run-key-persistence", "defender-exclusion-tampering", "rare-profile-binaries" ], "objective": "Determine if any host exhibits the PureCrypter behavior chain: environment sensing followed by persistence and execution of a rare binary in AppData.", "description": "Analyze the correlation between anti-analysis behavior, persistence mechanisms, and rare binary execution.", "max_iterations": 4, "expected_signal": "A per-host verdict of malicious, suspicious, or benign.", "success_criteria": "A detailed verdict citing process paths, registry keys, and specific WMI queries." }, "parents": [ { "id": "purecrypter-evasion-checks", "kind": "merge" }, { "id": "run-key-persistence", "kind": "merge" }, { "id": "defender-exclusion-tampering", "kind": "merge" }, { "id": "rare-profile-binaries", "kind": "merge" } ] }, { "id": "routing-decision", "type": "checkpoint", "label": "Route based on verdict", "config": { "fuzzy": true, "judge": "hunter", "question": "the triage verdict is malicious for at least one host and confirms ransomware execution indicators", "condition": "the triage verdict is malicious for at least one host and confirms ransomware execution indicators", "blind_spot": "missing-script-telemetry", "confidence": "high", "description": "Decide whether to isolate the host or move to analyst review.", "checkpoint_type": "mandatory" }, "parents": [ { "id": "triage-agent" } ] }, { "id": "isolate-host", "type": "action", "label": "Isolate host", "config": { "target": "endpoint", "description": "Prevent further spread of ransomware by isolating the affected host.", "instructions": "Isolate the host immediately via EDR/Identity control. Collect the rare binary from the identified AppData path for forensic analysis.", "action_approval": "required" }, "parents": [ { "id": "routing-decision", "branch": "on_supports" } ] }, { "id": "analyst-review", "type": "task", "label": "Analyst confirmation and tuning", "config": { "assignee": "analyst", "description": "Conduct a manual review of the agent's findings to confirm the intrusion and tune future detections.", "instructions": "Verify the rare process activity and check for signs of volume shadow copy deletion or mass file encryption on the identified hosts." }, "parents": [ { "id": "routing-decision", "branch": "default" }, { "id": "routing-decision", "branch": "on_unavailable" }, { "id": "isolate-host" } ] }, { "id": "close-out", "type": "task", "label": "Close out hunt", "config": { "assignee": "analyst", "description": "Finalize the hunt when no malicious activity is identified.", "instructions": "Log the hosts examined and confirm no PureCrypter/Mallox indicators were found. Retain the scoping results for the next monthly run." }, "parents": [ { "id": "routing-decision", "branch": "on_refutes" } ] } ] }