EncystPHP: Waffe des FreePBX-Web-Shells für dauerhafte Administratorenkompromittierung

Ruslan Mikhalov Leiter der Bedrohungsforschung bei SOC Prime

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EncystPHP: Waffe des FreePBX-Web-Shells für dauerhafte Administratorenkompromittierung

Detection stack

AIDR
Alert
ETL
Query

Bedrohungsbericht
Angriffsablauf
Erkennungen
Simulationen

Zusammenfassung

FortiGuard Labs berichtet über eine PHP-Web-Shell namens EncystPHP die auf exponierten FreePBX-Instanzen durch Ausnutzung von CVE-2025-64328eingesetzt wird. Das Implantat ermöglicht die Ausführung von Remote-Kommandos, bietet privilegierte Benutzerkonten und setzt durch Cron-Jobs und nachfolgende Dropper eine mehrschichtige Persistenz. Die Aktivität wird mit der INJ3CTOR3-Crew in Verbindung gebracht und scheint auf Telekommunikationsumgebungen abzuzielen. Veröffentlichte Indikatoren umfassen bösartige IPs, Domains, URLs und mehrere feindliche Dateipfade.

Untersuchung

Ermittler verfolgten den ersten Zugang auf eine nach Authentifizierung auftretende Kommando-Injektionsschwachstelle im FreePBX Endpoint Manager zurück. Nach erfolgreicher Ausnutzung zieht der Betreiber einen Dropper von 45.234.176.202, lockert die Berechtigungen für wichtige PHP-Komponenten, extrahiert Datenbankanmeldedaten, erstellt ein Root-Konto und fügt einen vom Angreifer kontrollierten SSH-Key hinzu. Die Persistenz wird durch Cron-Einträge verstärkt, die wiederholt zusätzliche Dropper abrufen und Artefakte aktualisieren. EncystPHP gibt sich auch als legitime FreePBX-Dateien aus und manipliert Zeitstempel, um die Sichtbarkeit während der routinemäßigen Überprüfung zu reduzieren.

Abmilderung

Patchen Sie den FreePBX Endpoint Manager, um CVE-2025-64328 (und alle damit verbundenen Fixes) so schnell wie möglich zu adressieren. Suchen Sie nach unautorisierten Web-Shell-Dateien, verdächtigen Cron-Planungen und neu erstellten privilegierten lokalen Benutzern. Blockieren Sie ausgehenden HTTP-Verkehr zu bekannten bösartigen Infrastrukturen und erzwingen Sie strenge, minimal notwendige Berechtigungen auf webbasierten Verzeichnissen und PHP-Ressourcen.

Reaktion

Bei Erkennung isolieren Sie den betroffenen PBX-Server, entfernen EncystPHP-Artefakte, löschen unautorisierte Cron-Jobs und setzen lokale Konten und SSH-Schlüssel zurück. Überprüfen Sie Protokolle und Konfigurations-Backups, um Änderungen zu erfassen, und wenden Sie aktuelle Sicherheitsupdates an. Härten Sie die Webschnittstelle. Stellen Sie sicher, dass keine sekundären Dropper oder Persistenzmechanismen verbleiben, bevor Sie den normalen Telefoniebetrieb wiederherstellen.

graph TB %% Class Definitions classDef action fill:#99ccff classDef tool fill:#ffcc99 classDef file fill:#ccffcc classDef process fill:#ffeb99 %% Nodes initial_access[„Action – T1190 Exploit Public-Facing Application Ausnutzung des FreePBX Endpoint-Managers CVE-2025-64328“] class initial_access action tool_wget[„Tool – Name: wget Description: Herunterladen von Dateien über HTTP“] class tool_wget tool process_shell[„Process – T1059.004 Command and Scripting Interpreter: Unix Shell Base64-dekodierte Bash-Skripte c, k.php, test.sh“] class process_shell process file_c[„File – c (Bash-Skript)“] class file_c file file_kphp[„File – k.php (PHP-Dropper)“] class file_kphp file file_testsh[„File – test.sh (Bash-Skript)“] class file_testsh file credential_access[„Action – T1003 OS Credential Dumping Datenbank-Zugangsdaten aus /etc/freepbx.conf gesammelt“] class credential_access action file_freepbxconf[„File – /etc/freepbx.conf“] class file_freepbxconf file priv_esc_exploit[„Action – T1068 Exploitation for Privilege Escalation“] class priv_esc_exploit action account_create[„Action – T1136.001 Create Account: Local Account Root-Benutzer newfpbx mit vordefiniertem Passwort-Hash erstellt“] class account_create action persistence_webshell[„Action – T1505.003 Server Software Component: Web Shell EncystPHP als ajax.php und config.php getarnt bereitgestellt“] class persistence_webshell action file_ajaxphp[„File – ajax.php (Webshell)“] class file_ajaxphp file file_configphp[„File – config.php (Webshell)“] class file_configphp file persistence_cron[„Action – T1053.003 Scheduled Task/Job: Cron Cron-Jobs installiert, um k.php jede Minute herunterzuladen und auszuführen“] class persistence_cron action defense_perm_mod[„Action – T1222.002 File and Directory Permissions Modification: Linux Dateiberechtigungen auf 000 gesetzt und Zeitstempel manipuliert“] class defense_perm_mod action defense_masquerade[„Action – T1036.005 Masquerading Shells in legitim aussehenden Verzeichnissen platziert“] class defense_masquerade action defense_indicator_removal[„Action – T1070.004 File Deletion and T1070.006 Timestomp Logs, Cron-Einträge gelöscht und Zeitstempel angepasst“] class defense_indicator_removal action lateral_movement_ssh[„Action – T1021.004 Remote Services: SSH and T1098.004 SSH Authorized Keys Öffentlicher Angreifer-Schlüssel zu authorized_keys hinzugefügt“] class lateral_movement_ssh action command_and_control[„Action – T1105 Ingress Tool Transfer and T1071.001 Application Layer Protocol: Web Protocols Dropper von 45.234.176.202 mittels wget abgerufen“] class command_and_control action impact_hijack[„Action – T1496 Resource Hijacking PBX für nicht autorisierte ausgehende Anrufe missbraucht“] class impact_hijack action defense_impair[„Action – T1562.001 Impair Defenses and T1548 Abuse Elevation Control Mechanism Fehlerberichterstattung deaktiviert und Administrationskontext für Systemänderungen genutzt“] class defense_impair action %% Edges initial_access –>|uses| tool_wget tool_wget –>|downloads| file_c tool_wget –>|downloads| file_kphp tool_wget –>|downloads| file_testsh initial_access –>|leads to| process_shell process_shell –>|executes| file_c process_shell –>|executes| file_kphp process_shell –>|executes| file_testsh process_shell –>|leads to| credential_access credential_access –>|reads| file_freepbxconf credential_access –>|enables| priv_esc_exploit priv_esc_exploit –>|enables| account_create account_create –>|enables| persistence_webshell persistence_webshell –>|creates| file_ajaxphp persistence_webshell –>|creates| file_configphp persistence_webshell –>|enables| persistence_cron persistence_cron –>|creates| file_kphp persistence_cron –>|uses| tool_wget persistence_cron –>|sets| defense_perm_mod defense_perm_mod –>|supports| defense_masquerade defense_masquerade –>|supports| defense_indicator_removal persistence_webshell –>|supports| lateral_movement_ssh lateral_movement_ssh –>|enables| command_and_control command_and_control –>|provides| impact_hijack command_and_control –>|supports| defense_impair

Angriffsablauf

Angriffs-Erzählung & Befehle:
1. Laden Sie die EncystPHP-Web-Shell hoch – Der Angreifer erstellt einen Base64-codierten PHP-Payload und liefert ihn über einen HTTP-POST an das FreePBX-Web-UI, wodurch die Datei ajax.php im Verzeichnis /var/www/html/admin/views/ajax.php.
2. geschrieben wird. Setzen Sie restriktive Berechtigungen – Unmittelbar nach der Bereitstellung führt der Angreifer – Unmittelbar nach der Bereitstellung führt der Angreifer
3. aus, um die Shell vor normalen Benutzern zu verbergen und die Ausführung unter dem privilegierten Konto des Web-Servers zu erzwingen (T1222.002). Löschen Sie kritische Konfigurationen – Um die Erkennung zu beeinträchtigen und das System zum erneuten Laden mit der bösartigen Shell zu zwingen, entfernt der Angreifer die – Um die Erkennung zu beeinträchtigen und das System zum erneuten Laden mit der bösartigen Shell zu zwingen, entfernt der Angreifer die
4. – Um die Erkennung zu beeinträchtigen und das System zum erneuten Laden mit der bösartigen Shell zu zwingen, entfernt der Angreifer die Die Shell auslösen ajax.php – Ein einfacher HTTP-GET zur neu erstellten
führt den Payload aus und etabliert eine Rückwärtsschale (T1105, T1059.004). Regressionstest-Skript:Das Skript reproduziert die Schritte 1‑3 in einem kontrollierten Testverzeichnis (Das Skript reproduziert die Schritte 1‑3 in einem kontrollierten Testverzeichnis (
```
) um ein Produktionssystem nicht zu beeinträchtigen.
```

Aufräum-Befehle:

# cleanup_encystphp_simulation.sh
set -euo pipefail
TEST_ROOT="/tmp/freepbx_test"
sudo rm -rf "${TEST_ROOT}"
echo "Testumgebung bereinigt."

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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.