Hacking forums often double up as underground marketplaces where cybercriminals buy, rent, and sell all kinds of malicious illegal products, including software, trojans, stealers, exploits, and leaked credentials. Malware-as-a-service has contributed substantially to the growth of ransomware and phishing attacks (among other attack types) in the past year, as they lower the technical barrier to entry for criminals to carry out attacks.
While recently perusing one of these hacking forums during regular research activities, the Zscaler ThreatLabz team came across BlackGuard, a sophisticated stealer, advertised for sale. Blackguard is currently being sold as malware-as-a-service with a lifetime price of $700 and a monthly price of $200.
BlackGuard has the capability to steal all types of information related to Crypto wallets, VPN, Messengers, FTP credentials, saved browser credentials, and email clients.
In this blog, we share analysis and screenshots of the techniques this stealer uses to steal information and evade detection using obfuscation, as well as techniques used for anti-debugging.
Fig 1. Forum thread promoting the BlackGuard stealer
BlackGuard is a .NET stealer packed with a crypto packer. Currently, it is in active development and has the following capabilities:
Once executed, it checks and kills the processes related to antivirus and sandbox as shown in the figure below.
Fig 2. BlackGuard detects antivirus processes
The stealer contains a hardcoded array of bytes which is decoded in runtime to ASCII strings followed by base64 decoding. This allows it to bypass antivirus and string-based detection.
Fig 3. String decryption technique
BlackGuard checks for the infected device country by sending a request to “http://ipwhois.app/xml/” and exits itself if the device is located in the Commonwealth of Independent States (CIS).
Fig 4. Whitelist CIS
BlackGuard uses user32!BlockInput() which can block all mouse and keyboard events in order to disrupt attempts at debugging.
Fig 5. Anti-debugging technique
After all the checks are completed, the stealer function gets called which collects information from various browsers, software, and hardcoded directories, as shown in the screenshot below.
Fig 6. Stealer code
Fig 7. Features Posted on forum
BlackGuard steals credentials from Chrome- and Gecko-based browsers using the static path. It has the capability to steal history, passwords, autofill information, and downloads.
Fig 8. Browser stealing function
BlackGuard also supports the stealing of wallets and other sensitive files related to crypto wallet applications. It targets sensitive data in files such as wallet.dat that contain the address, the private key to access this address, and other data. The stealer checks for the default wallet file location in AppData and copies it to the working folder.
Fig 9. Crypto wallet stealing function
This stealer also targets crypto wallet extensions installed in Chrome and Edge with hardcoded extension IDs as shown in the figure below.
Fig 10. Crypto extensions stealing function
After collecting the information, BlackGuard creates a .zip of all the files and sends it to the C2 server through a POST request along with the system information like Hardware ID and country as shown in the figure below.
Fig 11. C2 Exfiltration code snippet
Fig 12. Traffic capture of exfiltration
Fig 13. Panel screenshot
Chrome, Opera, Firefox, MapleStudio, Iridium, 7Star, CentBrowser, Chedot, Vivaldi, Kometa, Elements Browser, Epic Privacy Browser, uCozMedia, Coowon, liebao, QIP Surf, Orbitum, Comodo, Amigo, Torch, Comodo, 360Browser, Maxthon3, K-Melon, Sputnik, Nichrome, CocCoc, Uran, Chromodo, Edge, BraveSoftware.
AtomicWallet, BitcoinCore, DashCore, Electrum, Ethereum, Exodus, LitecoinCore, Monero, Jaxx, Zcash, Solar, Zap, AtomicDEX, Binance, Frame, TokenPocket, Wassabi.
Crypto Wallet Extensions:
Binance, coin98, Phantom, Mobox, XinPay, Math10, Metamask, BitApp, Guildwallet, iconx, Sollet, Slope Wallet, Starcoin, Swash, Finnie, KEPLR, Crocobit, OXYGEN, Nifty, Liquality, Auvitas wallet, Math wallet, MTV wallet, Rabet wallet, Ronin wallet, Yoroi wallet, ZilPay wallet, Exodus, Terra Station, Jaxx.
NordVPN, OpenVPN, ProtonVpn, Totalcomander, Filezilla, WinSCP, Steam
Telegram, Signal, Tox, Element, Pidgin, Discord
While applications of BlackGuard are not as broad as other stealers, BlackGuard is a growing threat as it continues to be improved and is developing a strong reputation in the underground community.
To combat against BlackGuard and similar credential theft malware, we recommend that security teams inspect all traffic and use malware prevention tools that include both antivirus (for known threats) and sandboxing capabilities (for unknown threats). We also recommend training end users on the following:
Don’t use the same passwords for all the services and replace them on a regular cadence.
Use multi-factor authentication where applicable.
Avoid visiting unknown sites.
Avoid opening suspicious unknown files.
We have ensured coverage for the payloads seen in these attacks via advanced threat signatures as well as our advanced cloud sandbox.
Advanced Threat Protection:
Advanced Cloud Sandbox:
Fig 14. Zscaler sandbox detection
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