BlueFox Stealer: a newcomer designed for traffers teams

This blog post on BlueFox Stealer is an extract of the “FLINT 2022-053 – BlueFox Stealer: a newcomer designed for traffers teams” report (SEKOIA.IO Flash Intelligence) sent to our clients on October 20, 2022.

Table of contents

• Introduction
• The emergence of BlueFox Stealer on forums
  • Another stealer designed for traffers teams
  • A look at distamx’s business
• Technical overview of BlueFox Stealer
  • Malware sample association
  • Malware capabilities
• Conclusion
• Technical Details & IoCs
• MITRE ATT&CK TTPs
• External References

Introduction

In 2022, information stealers are one of the most challenging threats for both companies and individuals. Cybercriminal threat actors distribute these malware to steal sensitive information from infected hosts, which are then sold on underground marketplaces, exploited for fraud (Business Email Compromise, E-Shop, Bank, Cryptocurrency theft), or leveraged in “Big Game Hunting” operations.

Malware developers take advantage of a growing demand for MaaS (Malware-as-a-Service) within the cybercrime ecosystem to sell their newly implemented or rebranded information stealers. They use various underground forums, as well as Telegram channels to advertise, manage financial transactions, and offer technical support. SEKOIA.IO monitor cybercrime forums to discover emerging malware, among other threats.

In early September 2022, through our Dark Web monitoring routine we identified a newly advertised malware dubbed BlueFox Stealer v2, and sold as a MaaS. Based on the ads promoting it, the BlueFox developer implemented a stealer tailored to the needs of traffers teams (including wide stealing capabilities, performance, efficiency, adapted to traffers context).

Based on this information, SEKOIA.IO assess that BlueFox Stealer is possibly to be added to the malware arsenal of traffers teams, similarly to Redline, Vidar, Raccoon Stealer v2, Aurora Stealer or Erbium Stealer, to be distributed at a large scale. This FLINT goes back to the emergence of BlueFox on cybercrime forums and presents a technical overview of it.

The emergence of BlueFox Stealer on forums

Another stealer designed for traffers teams

BlueFox Stealer’s first version appeared on Russian-speaking underground forums (XSS, BHF and DarkNet forums) in December 2021, and it was advertised by a threat actor going by the handle distamx. The lack of interactions on its publications may suggest that the project did not work as expected, for unknown reasons.

On 2 September 2022, the user distamx published a new post announcing version 2 of BlueFox Stealer on the XSS forum. This time, the publication resulted in more activity, including technical and business inquiries, positive feedback, as well as the release and changelogs of multiple updates (versions 2.0.4 to 2.0.7) by the alleged developer.

Among notable changes, the malware developer added an interesting feature to the administration panel of the BlueFox Stealer version 2.0.7 to allow traffers teams to operate the malware builds internally. Thus, traffers teams distributing the BlueFox Stealer have statistics related to each traffer (also named worker) and can give it access – making the integration of the BlueFox Stealer easier into the traffers teams resources. In other words, each traffer of the team can monitor statistics related to the distribution of their build on a non-authenticated webpage, and therefore have an assessment of the impact of their work.

SEKOIA.IO observed that efforts towards facilitating the integration of stealers in the traffers teams’ activities became common for infostealer developers. A second example is Lumma (aka LummaC) Stealer, another emerging malware advertised on Russian-speaking forums and sold as MaaS since August 2022. On 3 October 2022, its author Shamel published an update intended for the traffers teams, integrating a similar feature to display statistics by traffer.

A look at distamx’s business

The business model adopted by distamx is a classic among MaaS operators. The BlueFox Stealer author sells its malware and the related support services for $350 per month. Based on feedback and changelogs, distamx is very responsive to bug fixes and feature requests.

On 7 October 2022, distamx closed the sales of BlueFox Stealer v2, as the threat actor gained enough clients for work, according to its statement. We assess that the infostealer is under continuous development and the distamx’s workload is sufficiently high with the malware development and the customer responsiveness. It is therefore plausible that this will result in an increase of BlueFox activities in the near term if MaaS customers distribute it at large scale.

It is worth mentioning that distamx also advertised the malware in a Telegram channel (t[.]me/distamx_sup) similarly to what other MaaS operators were observed doing. BlueFox’s presence on Telegram resulted in scams impersonating distamx to lure potential customers. SEKOIA already observed such scams, notably for Mars Stealer, Aurora Botnet, and Raccoon. These scams are common in the Russian-speaking cybercrime ecosystem, and analysts monitoring malware-related activities should be aware of this so as not to follow false leads when investigating threat actors.

Technical overview of BlueFox Stealer

Once an emerging malware appears on cybercrime forums, SEKOIA.IO analysts implement search techniques to retrieve related samples or servers, to produce actionable intelligence to our customers.

Malware sample association

A few weeks after the launch of BlueFox Stealer v2, we retrieved BlueFox-related malware samples (SHA256 are available in the IOCs section). Here are the main technical details allowing SEKOIA to confirm association of these sample to BlueFox stealer with high confidence:

Of note, this is not an exhaustive list, rather a selection of the most characteristic technical artifacts deemed relevant in our association process.

BlueFox Stealer Malware capabilities

The BlueFox Stealer v2 capabilities advertised by distamx are those of a classic information stealer, with a focus on cryptocurrency wallets, and file grabber and loader capabilities.

Here is an overview of its capabilities:

• Targeting of popular browsers (Chromium and Firefox based browsers: Chrome, Edge, Opera, Mozilla, etc.) to steal passwords, cookies and autocompletes;
• Targeting of almost all desktop cryptocurrency wallets and extension for cryptocurrency wallets (MetaMask, TronLink, BinanceChain, Yoroi, Coinbase, Jaxx, Ethereum, Electrum, Exodus,
  etc.);
• Targeting password extensions (Bitwarden, 1Password);
• File downloading and loading;
• File grabbing in all disks;
• Screenshot capturing;
• System fingerprinting.

BlueFox exfiltrates the collected data to its C2 server using socket communication via native protocol on TCP/IP in encrypted form. The malware removes itself from the infected host using the Windows command cmd.exe /C timeout 5 & del "$PATH“.

A dynamic analysis from the Hatching Triage sandbox of a BlueFox Stealer v2 sample is available
here: https://tria.ge/221015-2ckbtagec3/behavioral2.

Conclusion

SEKOIA.IO assess that implementing features for monitoring traffers statistics when distributing information-stealing malware is likely to become a must-have to be a relevant player in the cybercrime ecosystem. Based on our observations, such capabilities are already quite common for prevalent loaders used by Pay-Per-Install services, such as SmokeLoader, PrivateLoader, and MixLoader.

To provide our customers with actionable intelligence, SEKOIA.IO analysts will continue to monitor BlueFox, emerging and prevalent infostealers; and keep an eye on the evolution of newcomers.

Technical Details & IoCs

BlueFox IoCs

BlueFox C2

The list of IoCs is available on SEKOIA github repository.

BlueFox samples

BlueFox2.0.8

194ef023286a19eea2c084f0d469d3427b97445b0b8fc75888d02274bf01e748
36190e8a9976de1036976ed44456ca833d7d2a7f23ed8acc707efe09fca7da9d
ca6d6555b349612637522e8506592ccaa5b0435f2a9af35aab77520cab495439
9ed0f76449bbc6d5d6db12dfc527740c072436c4379248855729321032d91bb7
82ce28407b4f0075d288470410df5af7c28e69ab44144bcf4610e6493e99e478
80bc9d060c42ada4ad5029a196293280d64257db95f223964ce7881930fab0f6
5e14e2582a02b6fe7cb28d6cad80bcddc51be2c01db097b0d292dfd575cb44a9

BlueFox2.0.7
7b7714d0bba4aa994d27130165a99d74cf627469f14ad7ba25c51ea0a1e16699
d8ca57e29b21ef3218877f43f9566f2fdbb11552f901d03234e3e9145c862392

BlueFox2.0.5
c56a00b4b8ebc12b8798e6ec7ab8e2c9815716fa40bb92488cb3e5c8a227d455

BlueFox2.0.4
186f94743c27032ff7401153a52116b4bbbf87c958dd0e2da1c0c111671c0563

BlueFox Stealer YARA rule

rule infostealer_win_bluefox {
    meta:
        malware = "BlueFox"
        description = "Find BlueFox Stealer v2 samples based on the specific strings embed in the executable files"
        source = "SEKOIA.IO"
        reference = "https://blog.sekoia.io/bluefox-stealer-a-newcomer-designed-for-traffers-teams/"
        classification = "TLP:CLEAR"

    strings:
        $str01 = "DesktopScreenshotLength" ascii
        $str02 = "SoftwareSearchesCount" ascii
        $str03 = "AutoCompleteLength" ascii
        $str04 = "DesktopSizeLength" ascii
        $str05 = "CPULength" ascii
        $str06 = "GPUsLength" ascii
        $str07 = "FullNameLength" ascii
        $str08 = "Asn1NssLength" ascii
        $str09 = "LoginLength" ascii
        $str10 = "BrowserCount" ascii

    condition:
        uint16(0)==0x5A4D and 9 of them
}

MITRE ATT&CK TTPs for BlueFox Stealer

External References

• https://blog.sekoia.io/traffers-a-deep-dive-into-the-information-stealer-ecosystem/

You can also read other blog post :

• EternityTeam: a new prominent threat group on underground forums
• Raccoon Stealer v2 – Part 1: The return of the dead
• Mars, a red-hot information stealer

• Traffers: a deep dive into the information stealer ecosystem
• Raccoon Stealer v2 – Part 1: The return of the dead
• Aurora: a rising stealer flying under the radar
• Stealc: a copycat of Vidar and Raccoon infostealers gaining in popularity – Part 1
• Stealc: a copycat of Vidar and Raccoon infostealers gaining in popularity – Part 2
• Calisto show interests into entities involved in Ukraine war support

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