Oski Stealer Malware

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Oski Stealer

The Oski Stealer is a malware which steals private information of the user, including crypto wallet details. It typically spreads by created targeted phishing attacks to trick the recipient into downloading an infected Microsoft Office file (such as PowerPoint). Once the file is downloaded, that installs malware which obtains data and can also launch other "command and control" functions. While the software does target many cryptocurrency wallets, it's unclear how successful the attacks have been as it tends to target unsophisticated business workers and not crypto users who would typically use such wallets.

This is a global/international case not involving a specific country.

About Oski Stealer

"First observed around November 2019, Oski Stealer is a popular threat, used to gather credentials and/or financial data from victims, and is readily available to purchase on various cybercriminal forums, typically advertised by a threat actor known as ‘oski_seller’, for around US$70-100 (Figure 1)." "As the name implies, the Oski stealer steals personal and sensitive information from its target. “Oski” is derived from an old Nordic word meaning Viking warrior, which is quite fitting considering this popular info-stealer is extremely effective at pillaging privileged information from its victims."

"Attackers try to trick users into installing Oski by hijacking router DNS settings in order that browsers then open corrupted pages and pop-ups. This motivates visitors to put in an application designed to deliver the latest information referring to the COVID-19. In fact, the file that’s downloaded through these malicious sites installs Oski, a trojan horse capable of stealing sensitive information." "[W]hen the settings are configured to use DNS servers operated by the attackers/cyber criminals. The servers redirect victims to an address displaying a web page encouraging them to download and install Oski, which is disguised as a legitimate app from the World Health Organization (WHO)."

"Given the nature of the email lure, recipients targeted will likely include those working within Business Administration, Finance and Sales teams. Furthermore, the compromise of one organization could lead to legitimate email accounts being abused to send convincing lures to other organizations, such as their customers, partners and suppliers." "Having lured the victim into opening the malicious email attachment, a weaponized Microsoft PowerPoint (PPT) file in this case, albeit easily interchangeable for some other Microsoft Office file, the victim is prompted to ‘Enable Editing’ and ‘Enable Content’ resulting in an embedded macro (Figure 4) being executed to download and initiate the first stage Powershell script. Whilst lightly obfuscated, this macro creates a Windows Scripting Host Shell Execution object, wshshell.exec, that executes the Microsoft HTML Application process, mshta, to send a HTTP GET request to a ‘Bit.ly’ shortened URL."

"Having redirected to a Blogspot-hosted page, the resulting HTML file (Figure 6) contains a Visual Basic script that is used to ultimately download and launch Agent Tesla that, in turn, downloads and launches Oski Stealer." "Using basic obfuscation, the Visual Basic Script downloader launches a hidden PowerShell window (-w 1), calling the Invoke-Expression (i'E'x) and Invoke-WebRequest (iwr) cmdlets to download and execute a PowerShell script named divine.txt from ‘Archive.org’. The hosting of content on this legitimate service is likely an attempt to avoid detection whilst allowing the delivery method to be updated mid-campaign without the needing to manage infrastructure such as domains and/or VPS instances."

"Cyberint Research observed a number of unsolicited malicious email (malspam) campaigns throughout July 2021 in which Agent Tesla has been used to deliver ‘Oski Stealer’ to a variety of targets worldwide." "In addition to being actively sold and supported by the original creator, unverified forum posts suggest that a ‘cracked’ version of Oski Stealer was leaked toward the end of 2020 (Figure 2) that, if true, could potentially lead to broader adoption."

"The stealer is written in C++ and has all the typical features of credential theft malware. Oski targets sensitive information including login credentials from different applications, browser information (cookies, autofill data and credit cards), crypto wallets, system information, screenshots, [and] different user files." "It also attempts to steal databases that contain 2FA (two-factor authentication) data, cryptocurrency wallets, and text files, and can take screenshots of the victim's desktop and perform other dubious actions. In this way, cyber criminals behind Oski are able to hijack various accounts, including social media, email, cryptocurrency trading accounts, and so on."

"After infecting a machine, the malware attempts retrieving sensitive information from web browsers based on Chromium and Firefox along with a special focus on Filezilla and crypto wallets like Bitcoin Core, Ethereum, ElectrumLTC, Monero, Electrum, Dash, Litecoin, ZCash." "Bitcoin Core, Ethereum, ElectrumLTC, Monero, Electrum, Exodus, Dash, Litecoin, ElectronCash, ZCash, MultiDoge, AnonCoin, BBQCoin, DevCoin, DigitalCoin, FlorinCoin, Franko, FreiCoin, GoldCoin, InfiniteCoin, IOCoin, IxCoin, MegaCoin, MinCoin, NameCoin, PrimeCoin, TerraCoin, YACoinFiles from machine data about machine."

"Upon the completion of the data theft stage, Oski Stealer creates a compressed Zip archive containing all of this stolen data, and names this with an underscore followed by the first ten digits of the working directory name."

"Beyond these, the stealer can function as a Downloader to download a second-stage malware." Attackers "might [also] be capable of hijacking accounts that have an additional layer of protection beyond passwords. Cyber criminals misuse stolen accounts to make fraudulent purchases and transactions, spread spam campaigns, trick other users into paying money to them, steal identities, etc."

This is a global/international case not involving a specific country.

The background of the exchange platform, service, or individuals involved, as it would have been seen or understood at the time of the events.

Include:

• Known history of when and how the service was started.
• What problems does the company or service claim to solve?
• What marketing materials were used by the firm or business?
• Audits performed, and excerpts that may have been included.
• Business registration documents shown (fake or legitimate).
• How were people recruited to participate?
• Public warnings and announcements prior to the event.

Don't Include:

• Any wording which directly states or implies that the business is/was illegitimate, or that a vulnerability existed.
• Anything that wasn't reasonably knowable at the time of the event.

There could be more than one section here. If the same platform is involved with multiple incidents, then it can be linked to a main article page.

The Reality

This sections is included if a case involved deception or information that was unknown at the time. Examples include:

• When the service was actually started (if different than the "official story").
• Who actually ran a service and their own personal history.
• How the service was structured behind the scenes. (For example, there was no "trading bot".)
• Details of what audits reported and how vulnerabilities were missed during auditing.

What Happened

The specific events of the loss and how it came about. What actually happened to cause the loss and some of the events leading up to it.

Key Event Timeline - Oski Stealer Malware

Date	Event	Description
October 3rd, 2021	Main Event	Expand this into a brief description of what happened and the impact. If multiple lines are necessary, add them here.

Technical Details

This section includes specific detailed technical analysis of any security breaches which happened. What specific software vulnerabilities contributed to the problem and how were they exploited?

Total Amount Lost

The total amount lost is unknown.

How much was lost and how was it calculated? If there are conflicting reports, which are accurate and where does the discrepancy lie?

Immediate Reactions

How did the various parties involved (firm, platform, management, and/or affected individual(s)) deal with the events? Were services shut down? Were announcements made? Were groups formed?

Ultimate Outcome

What was the end result? Was any investigation done? Were any individuals prosecuted? Was there a lawsuit? Was any tracing done?

Total Amount Recovered

There do not appear to have been any funds recovered in this case.

What funds were recovered? What funds were reimbursed for those affected users?

Ongoing Developments

What parts of this case are still remaining to be concluded?

General Prevention Policies

The basic protection is to not download any attachments from untrusted sources, and especially do not enable macros in a downloaded Microsoft Office file. Be extra careful if the file is of an unexpected type (for example a PowerPoint file when it's a purchase order). In general, all downloads should only be done from a trusted source. The vast majority of cryptocurrency should be stored fully offline when not being actively used.

Individual Prevention Policies

No specific policies for individual prevention have yet been identified in this case.

For the full list of how to protect your funds as an individual, check our Prevention Policies for Individuals guide.

Platform Prevention Policies

Policies for platforms to take to prevent this situation have not yet been selected in this case.

For the full list of how to protect your funds as a financial service, check our Prevention Policies for Platforms guide.

Regulatory Prevention Policies

No specific regulatory policies have yet been identified in this case.

For the full list of regulatory policies that can prevent loss, check our Prevention Policies for Regulators guide.