--- 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\u2014\ correlating three distinct surfaces into one high-fidelity verdict." blind_spots: - id: missing-script-telemetry question: Was the exclusion or payload download performed via an obfuscated VBScript or JScript? requires: hb_script_activity for non-PowerShell interpreters 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 - id: reflective-loading-blindspot question: Can we see the reflective loading of the stage 2 DLL or the final payload? requires: hb_module_activity 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 coverage: - stage: loader-evasion-and-anti-analysis status: covered steps: - purecrypter-evasion-checks - defender-exclusion-tampering - stage: persistence-run-key status: covered steps: - run-key-persistence - stage: mallox-ransomware-execution status: covered steps: - rare-profile-binaries - reason: Belongs to another part of the 'Mallox ransomware affiliate leverages PureCrypter in MSSQL exploitation' series. stage: sql-brute-force-access status: out_of_scope - reason: Belongs to another part of the 'Mallox ransomware affiliate leverages PureCrypter in MSSQL exploitation' series. stage: sql-server-exploitation status: out_of_scope - reason: Belongs to another part of the 'Mallox ransomware affiliate leverages PureCrypter in MSSQL exploitation' series. stage: initial-payload-delivery status: out_of_scope guardrails: claims: no_unsupported evidence: citation_required missing_data: not_benign telemetry: untrusted hunt: applicability: campaign-specific handoff: promote-to-detection 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. methodology: model-assisted trigger: intel-report 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. labels: - hunt - attack.t1497.001 - attack.t1562.001 - attack.t1129 - attack.t1547.001 - attack.t1486 - attack.t1047 name: PureCrypter evasion and Mallox ransomware execution parameters: lookback_days: default: '14' description: Days of history to examine. type: number malicious_usernames: default: - john - anna - xxxxxxxx description: Usernames checked by PureCrypter as part of anti-analysis; finding these in activity may indicate an evasion attempt. from: kind: article observed: '2024-05-02' ref: https://blog.sekoia.io/mallox-ransomware-affiliate-leverages-purecrypter-in-microsoft-sql-exploitation-campaigns/ type: list[string] mallox_filename: default: Ydxhjxwf.exe description: The specific ransomware filename observed in the report. from: kind: article observed: '2024-05-02' ref: https://blog.sekoia.io/mallox-ransomware-affiliate-leverages-purecrypter-in-microsoft-sql-exploitation-campaigns/ type: string scope_hosts: default: [] description: Optional list of hostnames to scope the hunt (e.g., confirmed MSSQL servers). type: list[host] provenance: authors: - name: Huntbase hunt generation org: huntbase.io 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 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. references: - name: Mallox ransomware affiliate leverages PureCrypter in MSSQL exploitation url: https://blog.sekoia.io/mallox-ransomware-affiliate-leverages-purecrypter-in-microsoft-sql-exploitation-campaigns/ 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 scenario: stages: - name: MS-SQL Brute Force 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) slug: sql-brute-force-access tactic: initial-access techniques: - T1110 - T1190 - name: MS-SQL Feature Exploitation 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 slug: sql-server-exploitation tactic: execution techniques: - T1059.003 - name: PowerShell Downloader and WMIC Execution 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 slug: initial-payload-delivery tactic: execution techniques: - T1059.001 - T1047 - name: PureCrypter Anti-Analysis and Evasion 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' slug: loader-evasion-and-anti-analysis tactic: defense-evasion techniques: - T1497.001 - T1562.001 - T1129 - name: Registry Run Key Persistence observables: - Registry key addition in 'Software\Microsoft\Windows\CurrentVersion\Run\' slug: persistence-run-key tactic: persistence techniques: - T1547.001 - name: Mallox Ransomware Execution observables: - Ransomware executable named 'Ydxhjxwf.exe' in %appdata% - Reflective code loading of stage 2 DLL - Elevation of process privileges with 'SeDebugPrivilege' slug: mallox-ransomware-execution tactic: impact techniques: - T1486 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. series: index: 2 slug: mallox-ransomware-affiliate-leverages-purecrypter-in-mssql-exploitation title: Mallox ransomware affiliate leverages PureCrypter in MSSQL exploitation total: 2 severity: high targets: analyst: name: Tier-2 analyst role: analyst endpoint: category: endpoint name: Endpoint telemetry (hb_ surfaces) telemetry: - endpoint hunter: agent: true name: Hunt agent tlp: clear type: investigation --- # PureCrypter evasion and Mallox ransomware execution 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. ## scope-mssql-servers Focus the hunt on hosts with Microsoft SQL Server installed, as they are the primary targets of this campaign. ```sqlite target=endpoint role=scoping ~~~yaml expected: A list of hostnames likely hosting SQL Server. If empty, the hunt runs across the full estate. reads: - device_hostname - package_name - vendor_name - asset_scope silence: not_evidence_of_absence source: hb_software_inventory verified: dry-run verified_at: '2026-09-17' ~~~ 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' ``` ## parallel-telemetry-gathering parallel: - → purecrypter-evasion-checks - → run-key-persistence - → defender-exclusion-tampering - → rare-profile-binaries join: → triage-agent ## purecrypter-evasion-checks Find process execution matching the loader's environment checks (WMI for BIOS/System) and the specific usernames it exits for. ```sqlite target=endpoint role=detection-candidate params=(scope_hosts=scope_hosts, malicious_usernames=malicious_usernames, lookback_days=lookback_days) ~~~yaml expected: Processes querying hardware identifiers or matching a known sandbox username. Finding BIOS/System WMI queries paired with ipconfig resets is highly indicative. reads: - device_hostname - process_cmd_line - user_name - time silence: not_evidence_of_absence source: hb_process_activity verified: dry-run verified_at: '2026-09-17' ~~~ 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') ``` ## run-key-persistence Identify the registry entry established by the loader to ensure survival after reboots. ```sqlite target=endpoint role=enrichment params=(scope_hosts=scope_hosts, lookback_days=lookback_days) ~~~yaml expected: A Run key pointing to a binary in a user-writable path. Normal applications usually install to Program Files. reads: - device_hostname - reg_target - reg_value_data - time silence: not_evidence_of_absence source: hb_registry_activity verified: dry-run verified_at: '2026-09-17' ~~~ 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') ``` ## defender-exclusion-tampering Find the PowerShell commands used to suppress Defender alerts for the ransomware binary. ```sqlite target=endpoint role=enrichment params=(scope_hosts=scope_hosts, lookback_days=lookback_days) ~~~yaml expected: Script blocks adding the loader or payload path to MpPreference exclusions. reads: - device_hostname - script_content - actor_user_name - time silence: not_evidence_of_absence source: hb_script_activity verified: dry-run verified_at: '2026-09-17' ~~~ 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') ``` ## rare-profile-binaries Stack-count processes running from AppData to highlight the Mallox binary against fleet background noise. ```sqlite target=endpoint role=baseline params=(scope_hosts=scope_hosts, mallox_filename=mallox_filename, lookback_days=lookback_days) ~~~yaml baseline: compare: first_seen window: '{{lookback_days}}d' expected: Binaries seen on only one or two hosts, specifically matching the reported Mallox filename or running from unusual AppData subdirectories. prevalence: by: device_hostname key: - process_path rare_below: 3 reads: - process_path - device_hostname - time - process_name silence: not_evidence_of_absence source: hb_process_activity verified: dry-run verified_at: '2026-09-17' ~~~ 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 ``` ## triage-agent ```agent target=hunter cite: required context: - purecrypter-evasion-checks - run-key-persistence - defender-exclusion-tampering - rare-profile-binaries max_iterations: 4 objective: 'Determine if any host exhibits the PureCrypter behavior chain: environment sensing followed by persistence and execution of a rare binary in AppData.' success_criteria: A detailed verdict citing process paths, registry keys, and specific WMI queries. tools: - endpoint ``` ## routing-decision if~: "the triage verdict is malicious for at least one host and confirms ransomware execution indicators" (confidence: high, judge=hunter) then: → isolate-host indeterminate: → analyst-review unavailable: → analyst-review (blind_spot: missing-script-telemetry) else: → close-out ## isolate-host ```action target=endpoint ~~~yaml approval: required ~~~ Isolate the host immediately via EDR/Identity control. Collect the rare binary from the identified AppData path for forensic analysis. ``` → analyst-review ## analyst-review ```manual target=analyst Verify the rare process activity and check for signs of volume shadow copy deletion or mass file encryption on the identified hosts. ``` → end ## close-out ```manual target=analyst Log the hosts examined and confirm no PureCrypter/Mallox indicators were found. Retain the scoping results for the next monthly run. ``` → end