Facebook has detailed a wide-scale Chinese malware campaign that targeted its ad platform for years and siphoned $4 million from users’ advertising accounts.
Dubbed SilentFade (short for “Silently running Facebook Ads with Exploits”), the malware compromised Facebook accounts and used them to promote malicious ads, steal browser cookies and more. The social-media giant said that the Chinese malware campaign started in 2016, but it was first discovered in December 2018, due to a suspicious traffic spike across a number of Facebook endpoints. After an extensive investigation, Facebook shut down the campaign and pursued legal action against the cybercriminals behind the attack in December 2019.
“Our investigation uncovered a number of interesting techniques used to compromise people with the goal to commit ad fraud,” said Sanchit Karve and Jennifer Urgilez with Facebook, in a Thursday analysis unveiled this week at the Virus Bulletin 2020 conference. “The attackers primarily ran malicious ad campaigns, often in the form of advertising pharmaceutical pills and spam with fake celebrity endorsements.”
Facebook said that SilentFade was not downloaded or installed by using Facebook or any of its products. It was instead usually bundled with potentially unwanted programs (PUPs). PUPs are software programs that a user may perceive as unwanted; they may use an implementation that can compromise privacy or weaken user security. In this case, researchers believe the malware was spread via pirated copies of popular software (such as the Coreldraw Graphics graphic design software for vector illustration and page layout, as seen below).
Once installed, SilentFade stole Facebook credentials and cookies from various browser credential stores, including Internet Explorer, Chromium and Firefox.
“Cookies are more valuable than passwords because they contain session tokens, which are post-authentication tokens,” said researchers. “This use of compromised credentials runs the risk of encountering accounts that are protected with two-factor authentication, which SilentFade cannot bypass.”
An example of a web page leading to the download of SilentFade. Credit: Facebook
The malware itself consists of three to four components, with the main downloader component being included in PUP bundles, researchers said. This downloader component is either a standalone malware component or a Windows service (installed as either “AdService” or ‘”HNService”). It’s responsible for persistence across reboots and for dropping 32-bit and 64-bit version dynamic library links (DLLs) in Chrome’s application directory, which are usually named winhttp.dll and launch DLL hijacking attacks.
“The DLL proxies all make requests to the real winhttp.dll but makes requests to facebook.com through the Chrome process, evading dynamic behavior-based anti-malware detection by mimicking innocuous network requests,” said researchers.
After stealing credentials, the malware retrieves the metadata about the Facebook account (such as payment information and the total amount previously spent on Facebook ads), using the Facebook Graph API, which is a legitimate Facebook feature allowing users to read and write data to and from the Facebook social graph. This data is then sent back to the malware’s C2 servers (as an encrypted JSON blob through custom HTTP headers).
SilentFade has varying persistence and detection-evasion tactics, including code to detect virtual machines (checking the description field of all available display drivers against “Virtual” or “VM” ) and halt execution when detected. It also disables Facebook notification alerts from compromised accounts, which could potentially alert the victim of suspicious activity.
And, in a unique anti-detection tactic, the C2 server stores the data and logs the IP address of the incoming request for the purpose of geolocation. “This was crucial as the attackers intentionally used the stolen credentials from the same or a nearby city to the infected machine to appear as though the original account owner has traveled within their city,” said researchers.
Ad fraud process using cloaking and legitimate user sessions retrieved by SilentFade. Credit: Facebook
While users’ Facebook credentials are valuable, users with credit cards linked accounts (for business accounts, for instance) also gave cybercriminals the ability to use those payment cards to promote malicious ads on Facebook.
However, “it should be noted that payment-information details (such as bank account and credit card numbers) were never exposed to the attackers, as Facebook does not make them visible through the desktop website or the Graph API,” said researchers.
As part of its investigations into SilentFade, Facebook also uncovered other Chinese malware campaigns, including ones dubbed StressPaint, FacebookRobot and Scranos. Some of these malware attacks remained active as recently as June, Facebook warned.
The company has faced security and privacy issues over the past year, and on Thursday filed a lawsuit in the U.S. against two companies that used scraping to engage in an international data harvesting operation, including scraping data from Facebook, Instagram, Twitter, YouTube, LinkedIn and Amazon, to sell “marketing intelligence.” The data involved includes names, user IDs, genders, dates of birth, relationship status, location information and more.
In the midst of all this, Facebook warns that it expects cybercriminals to continue to up the ante when it comes to launching attacks on its platform.
“We anticipate more platform-specific malware to appear for platforms serving large and growing audiences, as the evolving ecosystem targeting Facebook demonstrates,” said Facebook. “Only through user education and strong partnerships across the security industry will we measure the scale of malicious campaigns and effectively respond to them.”
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