Retour 
Summary
RedLine is an infostealer malware discovered in 2020. Often sold in underground forums, it is capable of stealing data such as credit card numbers, passwords, VPN and FTP credentials, gaming accounts, and even data from crypto wallets. In May 2022, Netskope Threat Labs analyzed a RedLine stealer campaign that was using YouTube videos to spread, luring victims into downloading a fake bot to automatically buy Binance NFT Mystery Boxes. Later in 2022, this malware was also spotted being self-spread through YouTube videos that were advertising popular gaming hacking tools.
In September 2022, Netskope Threat Labs found a RedLine Stealer campaign being spread through phishing emails. The email lures the user into opening a PDF file that redirects the victim to a URL that downloads RedLine, hosted on Discord.
Furthermore, we found that the attacker updated the same PDF file three times and didn’t flatten the latest version, which allowed us to retrieve three more URLs from older versions of the same file. These URLs download other malware from Discord, including PureCrypter and NjRAT (a.k.a. Bladabindi). NjRAT is another popular remote access trojan with many capabilities, such as logging keystrokes, stealing credentials from browsers, accessing the victim’s camera, managing files, and more.
In this blog post, we will analyze how this campaign works from the delivery method to the RAT payloads.
Delivery Method
The delivery method is fairly simple. The attacker sends a phishing email luring the user to open the attached PDF file, disguised as an invoice.
The PDF file contains an image that shows a blurred document, luring the user into clicking on a download icon that downloads RedLine from Discord.
By analyzing the PDF, we found older versions of the same file with different URLs the attacker was using, which are still online and delivering other malware instead of RedLine, as we will see later in this post.
This happens when the PDF is changed and isn’t flattened, keeping the update history within the objects.
RedLine Stealer
The latest URL in the PDF downloads a ZIP file from Discord that contains the RedLine Stealer payload, likely compiled on September 16, 2022.
As we covered in our previous blog, RedLine does not execute if the following countries are detected:
- Armenia
- Azerbaijan
- Belarus
- Kazakhstan
- Kyrgyzstan
- Moldova
- Russia
- Tajikistan
- Ukraine
- Uzbekistan
RedLine Stealer is able to steal sensitive information from specific apps, such as Discord and Steam, as well as from browsers and FTP and VPN clients.
Furthermore, the latest version of RedLine is also able to steal data from cryptocurrency extensions on Google Chrome.
This is the list of targeted Google Chrome extensions found in this specific sample:
- AtomicWallet
- Authenticator
- BinanceChain
- BitAppWallet
- BoltX
- BraveWallet
- Coin98Wallet
- Coinbase
- EqualWallet
- GuardaWallet
- GuildWallet
- HarmonyWallet
- iWallet
- JaxxxLiberty
- KardiaChain
- LiqualityWallet
- MaiarDeFiWallet
- MathWallet
- Metamask
- MewCx
- NamiWallet
- NiftyWallet
- Oxygen
- PaliWallet
- Phantom
- RoninWallet
- SaturnWallet
- TempleWallet
- TerraStation
- TonCrystal
- Tronlink
- Wombat
- XdefiWallet
- YoroiWallet
Lastly, we can find the RedLine Stealer C2 server and ID encrypted in its configuration. The data is base64 encoded and encrypted with a simple XOR algorithm using “Unhandier” as key.
The decrypted C2 server address can be found in our GitHub repository.
Older versions of the same PDF
As previously mentioned, we found three additional URLs by analyzing the update history of the PDF. At the time of the analysis, all the URLs were still online and downloading other malware.
Unlike RedLine Stealer, these other URLs were not downloading the final payload directly. Instead, they are downloading an HTA file (either directly or compressed) which is responsible for downloading and executing a payload, also hosted on Discord.
The first version of the PDF downloads a RAR file (“Invoice_NO355449609.rar”) with a compressed HTA file, which contains a Visual Basic Script that downloads the next stage payload (“Server.exe”) from Discord using bitsadmin.