It’s been a pretty big year so far for cryptocurrency. After it reached an all-time high in April 2021, new investors desperate not to miss out on the digital gold rush flocked to the exchanges to buy Bitcoin and altcoins. Cryptocurrencies’ current total market cap sits just above $1.7 trillion. The cryptocurrency exchange Coinbase recently launched an IPO, India has reversed a ban on cryptocurrencies, and ransomware groups continue to demand payment in anonymity-based cryptocurrency. I’ve even seen advertisements for Bitcoin on public transport during my commute.

The rush to buy has meant that many new to the cryptocurrency scene are investing without fully understanding how the currencies work. This has left the door open for cybercriminals to scam, steal, and otherwise exploit this lack of knowledge. With the cryptocurrency space showing no signs of slowing down, we review the most common attack vectors cybercriminals have discussed on cybercriminal forums in 2021, mitigations for these techniques, and examine how threat actors are adapting proven methods to target this new wave of users.

What are the most commonly discussed crypto attack vectors?

The most common vectors discussed across cybercriminal forums in recent months are:

  • Reverse proxy phishing
  • Cryptojacking
  • Dusting
  • Clipping

Reverse proxy phishing is a sort of domain-spoofing Man-in-the-Middle (MitM) attack whereby an attacker secretly “listens” to traffic between two unsuspecting parties. This technique is used to bypass two-factor authentication (2FA).

Cryptojacking is essentially the exploitation of your CPU’s labor,  where threat actors leverage a victim’s CPU to mine cryptocurrency. Marx would be livid!

Cryptocurrency “dusting” is deanonymizing your crypto wallet by sending tiny amounts of crypto “dust” to multiple wallets. Threat actors then monitor these wallets’ transactions and perform a combined analysis of different addresses on the blockchain to uncover the identity of the entity behind each wallet.

Cryptocurrency “clipping” is stealing cryptocurrency in the process of a transaction through the use of malware that automatically substitutes the intended wallet address with the threat actor’s wallet address.

Reverse-proxy phishing and mitigations

It’ll come as no surprise that cybercriminals are just as likely to employ phishing techniques to steal money from your crypto wallet as they are to drain your bank account. However, as many cryptocurrency platforms strongly encourage the use of two-factor authentication (2FA) methods such as authenticator apps, gaining access to your crypto accounts isn’t so simple. Authenticator apps mean that threat actors can’t just input credentials obtained during a phishing campaign to access your wallet. Nor can they employ SIM swapping techniques to intercept one-time passcodes (OTPs) delivered via SMS. This is where reverse proxy phishing, also known as “session hijacking,” comes into play.

Figure 1. Cybercriminal vendor advertising rates for reverse proxy phishing services targeting high-profile platforms
  1. The victim visits a fake domain they likely found in a spam email, e.g. www.c0inbase[.]com/login
  2. This fake domain is hosted on a malicious reverse proxy server that sits in between the victim and the server hosting the real login page. The reverse proxy server can monitor and control any traffic passing through.
  3. The reverse proxy server retrieves the legitimate login page and loads a copy for the victim. Fraudulently obtained SSL certificates ensure the victim’s browser does not detect that the fake webpage is a copy.
  4. The victim enters their login credentials on the fake page and is asked to perform two-factor authentication.
  5. The malicious server relays these credentials and 2FA code to the real login page on the real server.
  6. The real server verifies the credentials and, if correct, grants account access to the reverse proxy server, which it thinks is the victim client. The reverse proxy server can now control the session and cut the victim out – hence the term “session hijacking.” The attacker can now send any cryptocurrency to their own wallet.

It’s extremely hard to stop this type of attack once it has started. The fake page hosted on the reverse proxy server will be an exact copy of the real login page; only the URL will be different. The only 2FA method that is not vulnerable to such an attack is using a security key, as the key will refuse to authenticate on the malicious domain on the reverse proxy server. Such devices are not widely used, however, and so the best defense is not visiting the fake domain.

Standard phishing defense applies. Be skeptical of emails with clickable links and always double-check the sender’s email address and intended URL are correct. If you need to log in to an exchange or hot wallet, never do so via an email. Always navigate to the legitimate home page.

Cryptojacking and mitigations

Not all cybercriminals keen on increasing their cryptocurrency stacks need to steal from your wallet. Some can steal your processing power to mine their own coin instead. Botnets typically carry out cryptojacking, or “hidden mining.” Victims may be infected via a malicious link containing an .exe file that turns their machines into remotely controlled “zombies.” Attackers then install “miner” malware that runs in the background on a victim machine and can then secretly mine criminal-friendly cryptocurrencies such as Monero or Zcash. These miners are highly sought after on cybercriminal forums due to the expertise needed to build an effective tool. They’re typically written in low-level programming languages such as C++ or Assembler. They are designed to stay hidden on the victim’s system and often go undetected for years; vendors commonly advertise their miners’ detection rates by antivirus software.

Figure 2. Hidden miner vendor advertising detection rates of their malware via various antivirus programs

Attacks of this nature often have low barriers for entry. All a threat actor needs to do once they have purchased a botnet miner is get the victim to download it. Aside from the initial investment for the miner program and the cost of running the botnet, there is little overhead for the threat actor; vendors frequently advertise this method of attack as a source of “passive income.”

Not all cryptojacking leverages your CPU; there is also web-based cryptojacking. This uses scripts running on a website or domain so that when you visit the infected host your system will mine in the browser, which is a lot harder to spot. No company is off-limits for attackers: In 2017, Starbucks’s public Wi-Fi was hacked so that victims’ browsers mined Monero when accessing the network.

As none of your funds are stolen in a cryptojacking attack, you might wonder what the problem is. After all, these miners are hidden and may only run at certain times. However, if your machine is being used for mining, then your CPU performance will worsen and the lifespan of your hardware components will decrease. If a company’s corporate network is infected it can mean that outputs are reduced as staff are using slower machines.

Figure 3. Cybercriminal vendor advertises a hidden miner and Admin Panel

There are a few tell-tale signs of hidden miners. If your CPU usage is up, your machine’s making more noise than usual, or is slower to boot than you remember, you may be infected. Make sure to keep your antivirus updated. As always, be aware of any sketchy-looking links in emails from unknown senders. For web-based cryptojacking, install browser plugins such as AdBlock and MinerBlock, and avoid using public Wi-Fi. If you hold any crypto yourself, you should ensure you don’t have any mining malware installed on your machine, as many also serve as an entry point for the delivery of Trojan horses or other malicious software such as clippers.

Cryptocurrency clipping and mitigations

A backdoor trojan on your machine could allow a threat actor to deploy a particular malware called a cryptocurrency clipper, sometimes called a cryptocurrency stealer. These are also commonly downloaded as “innocent” third-party apps disguised as other programs like PDF readers, mobile games, or even COVID-19 tracers. These clipper programs prey on the lazy and those uneducated in cryptocurrency technology.

When you send cryptocurrency from one wallet or exchange, you must input the wallet address of the recipient – like inputting someone’s bank account number and sort code if you want to send them money. Clippers secretly substitute the wallet address of the intended recipient with that of the attacker during a cryptocurrency transaction. The clipper monitors the victim’s clipboard, where wallet addresses are copied. When the user goes to paste the wallet address of the intended recipient, they unknowingly paste the hijacked address instead.

Figure 4. Cybercriminal vendor advertises source code of a Bitcoin wallet clipper written in C#

This is actually a fairly simple attack to mitigate if you always double-check that the copied and pasted wallet addresses match. If you’re still unsure, another tactic is to send a small amount of currency to your intended recipient. If all goes through, then you can be confident about sending the rest. Finally, don’t download suspicious-looking apps from app stores. Pay attention to generic reviews from potential bot accounts and don’t give more permissions than necessary for the app to function (Doodle Jump doesn’t need to access your clipboard).

Dusting attacks and mitigations

Okay, this one’s a little more complicated, but it has larger implications for corporate cryptocurrency holders. Imagine you placed a dollar bill with a hidden tracker in a wallet you found on the floor. If you left the wallet on the floor and the owner came back for it, you might be able to tie their identity to a bank account if they later cashed this dollar in.

Figure 5. Cybercriminal forum user shares a guide for carrying out a dusting attack.

If a dusting attack is successful, the attackers may use this knowledge in elaborate phishing attacks. Imagine a spear-phishing email in which an attacker claims to be a client that hasn’t received their Bitcoin – if they can list your wallet address and transaction amount they’ll be a lot more successful at convincing you to send another payment.

The best way to mitigate a dusting attack is to generate a new wallet address for every transaction. If you’re really blockchain savvy, some wallets allow you to parse funds received so that you avoid using the “dust” in subsequent transactions.

How can I stay up to date on cybercriminal attack vectors?

As you can see, the attacks cybercriminals employ in 2021 to take advantage of the crypto craze are very advanced. In fact, even cybercriminals themselves fall victim to them. We’ve recently seen a few forum threads where threat actors complain about having their virtual currency stolen. One user even held an “ask me anything” session after they lost “100k” due to “being phished” in May 2021. Another wrote, “I want my currency back, this is god damn bad,” after their Etherium was stolen. It turns out you can steal from a thief.

Figure 6. Cybercriminal forum user announces AMA after being phished

The point is that it’s important to stay up to date with the current attack vectors in order not to become a victim. Staying vigilant can be tough, but here at Digital Shadows (now ReliaQuest) we constantly scour cybercriminal platforms to make sure our clients are aware of the new angles of attack. As cryptocurrency becomes ever more present in society, it’s likely that attackers will continue to refine their methods and invent new ones. Businesses will need to continuously update their security practices to stay on top.

To stay in the know about recent cybercriminal developments, sign up to a 7-day free trial of Threat Intelligence with SearchLight. SearchLight (now ReliaQuest’s GreyMatter Digital Risk Protection) clients receive real-time, actionable intelligence updates relating to new attack types, including analysis from our team of global analysts and intelligence on new posts to platforms across open and closed sources.