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Cyber Threats
PARASITESNATCHER: HOW MALICIOUS CHROME EXTENSIONS TARGET BRAZIL
We detail the modular framework of malicious Chrome extensions that consist of
various highly obfuscated components that leverage Google Chrome API to monitor,
intercept, and exfiltrate victim data.
By: Aliakbar Zahravi, Peter Girnus November 23, 2023 Read time: 12 min (3275
words)
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--------------------------------------------------------------------------------
Our investigations on potential security threats uncovered a malicious Google
Chrome extension that we named “ParaSiteSnatcher.” The ParaSiteSnatcher
framework allows threat actors to monitor, manipulate, and exfiltrate highly
sensitive information from multiple sources. ParaSiteSnatcher also utilizes the
powerful Chrome Browser API to intercept and exfiltrate all POST requests
containing sensitive account and financial information before the HTTP request
initiates a transmission control protocol (TCP) connection.
Our research shows that the malicious extension is specifically designed to
target users in Latin America, particularly Brazil; it exfiltrates data from
Banco do Brasil- and Caixa Econômica Federal (Caixa)-related URLs. It can also
initiate and manipulate transactions in PIX, a Brazilian instant payment
ecosystem, and payments made through Boleto Bancario, another payment method
regulated by the Bank of Brazil. We also observed that it can exfiltrate
Brazilian Tax ID numbers for both individuals and businesses, as well as
cookies, including those used for Microsoft accounts.
Once installed, the extension manifests with the help of extensive permissions
enabled through the Chrome extension, allowing it to manipulate web sessions,
web requests, and track user interactions across multiple tabs using the Chrome
tabs API. The malware includes various components that facilitate its operation,
content scripts that enable malicious code injection into web pages, monitor
Chrome tabs, and intercept user input and web browser communication.
It is worth noting that while ParaSiteSnatcher specifically targets Google
Chrome browsers, the malicious extension will also work on browsers that support
Chrome extension API and runtime, such as Chromium-based browsers like newer
versions of Microsoft Edge, Brave, and Opera. These extensions could potentially
be compatible with Firefox and Safari as well, but changes such as the browser
namespace are necessary.
The ParaSiteSnatcher downloader
ParaSiteSnatcher is downloaded through a VBScript downloader hosted on Dropbox
and Google Cloud and installed onto an infected system.
Our analysis has identified three distinct variants of the VBScript downloader,
which are characterized by differing levels of obfuscation and complexity:
*
* Variant 1. This variant presents a straightforward approach where the payload
is not obfuscated, making it relatively easier to analyze and understand.
*
* Variant 2. In this iteration, critical strings within the payload are
obfuscated using a Reverse String technique. This adds a layer of complexity
to the code, requiring a reverse operation to decipher the original content.
*
* Variant 3. This variant incorporates additional obfuscation techniques. It
includes junk code that serves to confuse the analysis process, anti-debug
and anti-tamper protections, alongside the use of randomly generated names
for variables and functions to prevent easy pattern detection. It also
utilizes Reverse String obfuscation to further conceal the payload,
presenting a more challenging structure for analysts to decipher.
Upon execution, the downloader performs an initial check for the presence of the
%ProgramFiles%\Google\Chrome\Application\chrome.exe file, and the
%APPDATA%\%USERNAME% folder. If found not present, the script will terminate its
process.
Figure 1. Verifying chrome installation and AppData path presence
The malware establishes communication with the attacker’s C&C by constructing
and sending a GET request to hxxps[:]//storage.googleapis[.]com/98jk3m5azb/-.
The response from the server is an obfuscated list of URLs.
The malware then de-obfuscates this list with a series of string manipulations
performed on the C&C response that reverses the string back to its original
order. It then replaces specific characters with their correct counterparts to
reconstruct the URLs:
*
* "[h]" is replaced with "https://", specifying the protocol part of the URL.
*
* "-" is replaced with ".", reconstructing the domain names.
*
* "_" is substituted with "/", fixing the path structure.
*
* ">" is replaced with ":", correcting port specifications.
Figure 2. De-obfuscating URLs from the C&C response
Once the actual URLs are retrieved, they are used to download additional
malicious modules masquerading as Google Chrome extensions.
Figure 3. The list of obfuscated URLs from the threat actor’s C&C response
The first URL from above list (hxxps[:]//rezumdolly[.]com:8443/api/alert) is
used to register an infected system and notify the attacker. The malware first
utilizes the Windows Management Instrumentation (WMI) service to perform a query
against the Win32_OperatingSystem class, which retrieves details about the
operating system that are subsequently sent to the attacker’s C&C server.
Figure 4. ParaSiteSnatcher gathers the victim’s system information upon arrival
It then constructs a .json-formatted string that encapsulates several pieces of
system information as follows:
* comp. The computer's name, which can be used to uniquely identify the system
on a network.
*
* user. The registered user's name, providing insights into who uses or owns
the system.
*
* version. The operating system version, indicating the specific build and
potential vulnerabilities.
*
* arch. The architecture of the operating system (e.g., 32-bit or 64-bit),
which is useful for tailoring further attacks to the system's specifications.
*
* caption. A descriptive label for the operating system, often including the
edition (e.g., Windows 10 Pro).
Figure 5. Registering an infected system with the attacker's command and control
server
The malware uses the down() function to download and save ParaSiteSnatcher
malicious extension modules on an infected system’s %APPDATA%\%USERNAME%
directory.
Figure 6. The ParaSiteSnatcher download function
The malware then attempts to locate and delete Chrome shortcuts by searching for
any shortcuts that contain "chrome.lnk" in the Desktop, Public Desktop, and
Quick Launch folders.
Figure 7. ParaSiteSnatcher removing Chrome shortcuts from the victim’s Desktop
and Quick Launch folders with VBScript
To achieve persistence on the victim’s system and load malicious execution on
every execution, the malware creates a Google Chrome shortcut on the desktop,
which is configured to launch the browser with custom startup parameters. These
parameters include the specification of a default user profile directory and the
initiation of a malicious browser extension housed within the user's application
data folder. This process is engineered to ensure that the malicious extension
is loaded each time Chrome is started via the created shortcut.
Figure 8. The malware’s persistence
Extension and C&C communication
Figure 9. A diagram showing how the different components of the ParaSiteSnatcher
Chrome extension communicate.
The communication mechanism employed by ParaSiteSnatcher Chrome extensions rely
heavily on using the Chrome sendMessage API to communicate with various
extension components when specific conditions are met.
When messages are received, the malicious Chrome extension executes internal
functions on these events: some components pass along the targeted and processed
and targeted data directly to the attacker C&C, while most of the other
components contain logic that can receive and update commands directly from the
threat actor.
The extension’s service worker, which we will discuss further into this blog,
leverages the chrome.windows and chrome.tabs API for navigating and focusing the
document object model (DOM) that other ParaSiteSnatcher components rely on.
Analyzing ParaSiteSnatcher Chrome extension files
In this section we explore the various files that comprise the ParaSiteSnatcher
Framework's malicious Chrome extension.
Figure 10. Properties of the malicious Chrome extension we investigated
manifest.json
Every Google Chrome extension includes a manifest.json file in its root
directory. This background manifest key contains essential information, such as
the extension’s name, version, permissions, and any scripts associated with the
Chrome extension. The extension uses a service worker (yyva.js) as part of its
background processes for handling tasks, orchestrating modules and data
synchronization in the background.
Figure 11. The manifest.json file in the ParaSiteSnatcher’s root directory
The manifest.json file contains the following:
* Basic metadata. This includes the name, description, version, and author key
of the browser extension.
* Service workers. These are JavaScript files that act as the extension's
primary event handler. These events include more than just servicing web
requests and can respond to events like navigating a new page, clicking
notifications, and opening or closing tabs. Not that Chrome makes the
critical distinction between a web service worker and an extension service
worker to highlight that the extension service worker is more than just a web
request proxy service. The service worker specified in the background key is
the extension service worker.
* Content scripts. These allow developers to statistically load JavaScript
files when webpages are opened that match a specific URL pattern.
* Permissions. These determine which capabilities are exposed to their
respective extension.
In the sample of the ParaSiteSnatcher extension we investigated, we saw some
critical content_script keys that determine what scripts are injected, where
they are injected, and how they behave:
* matches. This type of key specifies the pattern to be used for matching.
The <all_urls> value matches any URL that starts with a permitted scheme,
such as http, https, and file.
* run_at. This key specifies when the script should be injected into the page,
where the document_end value injects the script while the page resources are
still loading.
* all_frames. This is a Boolean value. When set to true, the extension will
inject scripts into all <iframe> elements even if the frame is not the
topmost in the tab.
* persistent. When the persistent Boolean value is true, the extension
developer can access the chrome.webRequest API to block or modify network
requests. This is the only use case for setting the persistent boolean to
true; by default, this value is set to false for performance reasons.
Additionally, the malicious extension contained host_permissions among the
permissions in its manifest file. The host_permission key grants extra
permissions for the extension’s API to read and modify host data such as
accessing the API cookies, receiving events using the webRequest API,
programmatically injecting scripts, bypassing tracking protections, and reading
tab-specific metadata. It can also access XMLHttpRequest and fetch access to
origins without cross-origin restrictions.
If an extension uses the host_permissions key, the user could be prompted to
grant these permissions to the extension. As of June 2023, Safari, Firefox, and
some Chromium-based browsers don't prompt the user during installation. In this
malicious sample, the host_permissions allow the extension to read and modify
all URLs using the <all_urls> value.
ParaSiteSnatcher also contains the permissions JSON key, which contains specific
WebExtension API keywords that the extension requests to use. The malicious
extension requests the following WebExtension JavaScript APIs:
* webNavigation. This API adds an event listener for various stages of
navigation, such as in response to a user action, like clicking a link or
adding a URL in the location bar.
* notifications. This API allows extensions to create and display
notifications to users in the system tray.
* declarativeNetRequest. This API allows extensions to specify conditions and
actions on handling network requests, allowing extensions to block and
upgrade network requests without explicit host permissions.
* declarativeNetRequestFeedback. This API allows extensions to access functions
and events that return information on declarative rules, such as those
through the declarativeNetrequest API.
* scripting. The scripting API allows the insertion of JavaScript into
websites, such as through the scripting.executeScript() and
scripting.registerContentScripts() methods.
* webRequest. The webRequest API grants access to add event listeners to HTTP
and WebSocket requests. These event listeners can receive detailed
information about such requests, including the ability to modify and cancel
these requests.
* storage. The storage API allows extensions to store and receive data and
listen for changes in stored data.
* tabs. The tabs API allows extensions to interact with the Chrome browser’s
tab system, including creating, modifying, and rearranging browser tabs. This
powerful API also includes taking screenshots and communicating with a tab’s
content scripts.
* activeTab. This API permits access to the currently active tab when users
execute browser and page actions.
* cookies. The cookies API allows the extension to query and modify cookies and
be notified of cooking changes.
It is important to note that many other API permissions exist in Chrome for
developers API Reference. From a security perspective, it is essential to
understand that web browser extensions can declare many permissions, and not all
extensions will request the user to grant explicit access. This highlights the
essential need to understand what any downloaded extension does and its declared
permission levels.
yyva.js
This component is an Extension Service Worker or Service Worker, the central
event handler for Google Chrome extensions that handles web events and messages
from other extension components. The extension service worker can respond
to standard service worker events in addition to extension events, such as
navigating to a new page, clicking a notification, or closing a tab. This
service worker is declared with the service_worker key.
In our research, all extension components are highly obfuscated, but after
deobfuscating each component and cleaning up the code, we uncovered the
following important extension service worker features working with the Chrome
API:
* Event listening and handling. The yavvy.js service worker is tasked with
listening for events using the chrome.runtime.onMessage.addListener API.
Within Chrome extensions, various components can leverage the Chrome API to
message each other using the sendMessage API. The service worker is
specifically tasked with listening for navigation, focus, and getcookies
messages.
*
* Listening and intercepting POST requests. The yavvy.js service worker uses
the Chrome.webRequest.onBeforeRequest.addListener to create a callback
function to listen for web request events containing a POST request, as well
as gather tab information using the chrome.tabs.get API, which it uses for
analysis.
Figure 12. ParaSiteSnatcher uses chrome.runtime.onMessage.addListener to listen
for specific events.
Despite its extensive listening, it is worth noting that ParaSiteSnatcher
excludes local network addresses and C&C domain from its monitoring.
Figure 13. ParaSiteSnatcher excludes local network addresses and C&C domain from
its monitoring.
It also intercepts and monitors user activity, and handles the following
messages received from other modules:
* messageDetails.type == 'focus'
*
* messageDetails.type == 'navigate'
*
* messageDetails.type == 'getcookie'
The functions that handle the navigate and focus events use the chrome.windows
and chrome.tabs API for navigating and focusing the document object model (DOM).
Other components of this malicious Chrome extension leverage these messages
extensively.
jsync.js (Jquery 3.3.1)
This file is injected as a Chrome extension dependency and is a content script
used primarily for Asynchronous JavaScript and XML (AJAX) communication with the
attacker C&C to exfiltrate sensitive data from infected users.
sovvy.js
This primary content script in the malicious Chrome extension periodically
monitors specific forms and elements on a webpage and sets up event listeners on
certain buttons every two seconds. It leverages the Chrome runtime API using the
chrome.runtime.onMessage.addListener API method to listen for the custom
messages passed between various extension events with the types, “lixo,”
“cookie,” and “timer.” When events with these message types are initiated, they
in turn trigger ParaSiteSnatcher to run these specific functions:
* Intercepting POST requests. The lixo message is a catch-all event and does
not look for specific URL patterns. Instead, it tracks all POST requests in
which the attackers search for sensitive information such as usernames,
passwords, emails, and credit card information.
Figure 14. ParaSiteSnatcher tracks all POST requests
* Stealing cookies and user sessions. The cookie message sends a POST request
to the attacker C&C for cookie and session theft.
Figure 15. ParaSiteSnatcher also gathers data related to cookies.
* Stealing Microsoft cookies. When cookies matching Microsoft live.com exist,
the sovvy.js file sends a message using the chrome.runtime.sendMessage API to
send this data to the service worker, which processes this data to filter and
extract the found Microsoft account cookies. These can be leveraged for
account theft and pass-the-cookie attacks as well as pivoting to the cloud.
Figure 16. ParaSiteSnatcher uses the chrome.runtime.sendMessage API to get a
victim’s user information related to Microsoft accounts.
* Stealing Banking Details. Our investigation of ParaSiteSnatcher revealed that
the malicious extension conducts multiple URL checks related to Brazilian
online banking companies, including Banco do Brasil and Caixa Econômica
Federal. When the victim interacts with URLs related to these financial
institutions, the malicious Chrome extension begins processing the data,
looking for items such as usernames, passwords, and credit cards numbers, and
sending the data with a POST request to the attacker’s C&C.
Figure 17. ParaSiteSnatcher looks out for communication with banking sites and
get password entries by victims
* Fetching commands from the attacker’s C&C. Within this the sovvy.js script is
the ability for the malicious Chrome extension to retrieve commands from the
attacker C&C server with a standard HTTP GET request.
Figure 18. sovvy.js contains script that retrieves commands from the threat
actor’s C&C server.
33nhauh.js
The 33nhuah.js file contains business logic to monitor bank account details and
perform PIX instant payment actions. PIX is an instant payment platform created
and regulated by the Banco Central do Brasil (Central Bank of Brazil).
Some key features of this content script include HTML templates for password
input forms, definitions for enum type data representing command types, account
information, PIX key types, and parameters for PIX transactions. This content
script also contains functions to monitor bank account balances and perform PIX
transactions. Additionally, there are functions that manipulate the user
interface, such as setting and resetting forms, clicking on menu items, and
hiding or loading process indicators.
This content script uses the standard HTML DOM selector to find specific
elements containing sensitive PIX elements such as receiving PIX institution
names, and user account information such as:
* CPF/CNPJ (Brazilian Individual & Business Taxpayer Registration) details
*
* Email addresses
*
* Cellphone numbers
*
* PIX Keys
Figure 19. ParaSiteSnatcher monitors activity related to PIX transactions,
gathers victim data from these transactions, and performs actions such as
navigating the PIX menu and selecting buttons within its interface.
unpgp2.js
The content script unpgp2.js is designed to navigate, focus, and interact with
the internet banking interface of the Caixa Econômica Federal’s web interface.
This content script performs various actions such as navigating pages, fetching
account details, focusing on elements, executing financial transactions and
initiating PIX transactions.
Figure 20. ParSiteSnatcher specifically looks for activity with URLs related to
Caixa Econômica Federal.
s12ih0a.js
This content script primarily contains logic that is used to periodically
monitor windows and tabs content specifically those that contain or are related
to the following:
* Boleto Bancário
*
* The CPF (Cadastro de Pessoas Físicas or Natural Persons Register) numbers of
both the payer and receiver in transactions
*
* The CNPJ (Cadastro Nacional da Pessoa Juridica or Taxpayer Identification)
number of both the payer and receiver in transactions
*
* Bank payment slips
The logic contained in this content script is called during specific intervals
to monitor the DOM and user-input through the sovvy.js content script. The
s12ih0a.js content script will also POST elements such as telephone numbers and
email addresses to the attacker C&C.
Figure 21. The ParaSiteSnatcher data exfiltration to its C&C server
In the following table, we summarize the functions of each ParaSiteSnatcher
extension component:
Module Name Functions yyva.js
async function timerMonitor()
function getCookies()
async function navigate()
async function setFocusTab()
function addLog()
async function analyzeRequest()
sovvy.js
function setCommandRetorno()
function updateCmd()
function timerMonitor()
function postSession()
function postLixo()
function getCmd()
function updateCmd()
function updateStatusOn()
function getVersion()
function getUser()
function getElement()
function addlog()
function trim()
function toLowerCase()
function extractDigits()
function getForm()
function preparePostData()
function buildInputMap()
function checkElementClick()
function checkInputPost()
function ValidateEmail()
function GenerateToken()
function SetToken()
function updateUserId()
33nhauh.js
function monitorBB()
function resetCommand_BB()
function getSaldo_BB()
function clickMenuSaldo()
function focoTab_BB()
function hideProcesso()
function action_pix_BB()
function checkComprovante()
function setSConta()
function setValor()
function setChave()
function clickMenuPix()
function clickMenu()
function setAccountPasswordForm()
function getAgencyAndAccountNumber()
function resetAccountPasswordForm()
s12ih0a.js
function monitor2Via()
function setEventDesco()
function setEventBB()
function click_isPagina()
function setMessageDesco()
function setMessageBB()
function setHtmlBB()
function setHtmlDesco()
function getDadosSegundaVia()
function post2Via()
function checkDebugging()
function innerFunction()
unpgp2.js
function monitorAzul()
function get_azul_ass()
function get_azul_Saldo()
function focoTab_Azul()
function resetCommand_Azul()
function get_azul_agcc()
function azul_pedidos_automaticos()
Conclusion
The use of malicious Google Chrome extensions by leveraging the powerful Chrome
API in ways specifically designed to intercept, exfiltrate, and potentially
modify sensitive user data underscores the importance of being vigilant when
granting permissions to extensions and when using web browsers.
ParaSiteSnatcher’s multifaceted approach to obfuscate its arrival onto victim’s
systems also ensures persistence and stealth, making detection and removal
efforts challenging, so users should be doubly watchful of the specific
extensions they download and install onto their browsers.
Despite our investigations showing that ParaSiteSnatcher specifically targets
Google Chrome browsers, users who utilize other browsers that are Chromium-based
and that support various APIs used by Chrome extensions should be equally wary.
Indicators of Compromise (IoCs)
You can find the full list of ParaSiteSnatcher IoCs here.
Tags
Articles, News, Reports | Cyber Threats | Research
AUTHORS
* Aliakbar Zahravi
Staff Researcher
* Peter Girnus
Sr. Threat Researcher
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