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Rhysida Using Oyster Backdoor in Attacks

Threat Actors

In July, the Rhysida ransomware group was observed using the Oyster backdoor malware as part of its attacks. This tactic is part of a broader malvertising campaign first reported in June by security researchers. In this new campaign, fake websites disguised as sites like Microsoft Teams are used to trick users into downloading what they believe are legitimate versions of the software, but instead are malicious installers that drop the Oyster backdoor on the victim’s system.

What’s Notable and Unique

  • Oyster malware – also known as Broomstick – uses a loader that looks like a legitimate software installer. When a user downloads the loader, the installer deploys the Oyster backdoor, which allows the threat actor to gather information about the victim’s system and steal credentials.

  • Although researchers observed Rhysida using the Oyster backdoor in an attack in July, Arete has observed the ransomware group using this technique since at least May 2024.

  • Rhysida is a ransomware-as-a-service (RaaS) that has been active since May 2023, but Arete has observed that the group has been considerably more active in 2024, with a notable spike in activity between June and August. Most recently, the group was responsible for the attack against the Port of Seattle in August, which disrupted systems at Seattle-Tacoma International Airport and resulted in several flight delays.

Analyst Comments

This recent malvertising campaign is a prime example of threat groups actively using search engine optimization (SEO) poisoning to lure victims to legitimate-looking websites and trick them into downloading malware. Although this technique is known to be exploited by a variety of actors, Rhysida has found recent success in using it to gain access to multiple victim systems and will likely continue to do so for as long as it remains effective. Even when using common search engines like Google, it is important that users pay attention to any links that have typos or seem suspicious. Employing active endpoint detection and response solutions is also critical in disrupting threat actor activity and mitigating the risk of a cyber-attack.

Sources

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Article

Current: Misconfigured Server Reveals Multiple Phishing Campaigns

Researchers uncovered three Microsoft 365 phishing campaigns after discovering a misconfigured HTTP server that exposed a threat actor’s phishing tools, configurations, victim logs, and operational infrastructure. The investigation revealed two operators using custom Evilginx-based adversary-in-the-middle (AiTM) phishing frameworks to steal authentication sessions and bypass MFA protections. A third operator abused Microsoft’s OAuth Device Code flow by tricking victims into completing authentication through Microsoft’s legitimate login process, allowing attackers to obtain valid access and refresh tokens without stealing passwords. The largest campaign compromised at least 218 victims across 12 countries, primarily targeting corporate Microsoft 365 accounts, with refresh tokens enabling persistent access. Researchers also identified the use of remote management tools for maintaining access, AI-assisted development of phishing tooling, and links to broader Phishing-as-a-Service (PhaaS) ecosystems, highlighting how commodity frameworks and automation are lowering the barrier for sophisticated identity-based attacks.

What’s Notable and Unique

  • The campaigns demonstrate the continued shift from traditional credential theft to identity- and token-based compromise, in which attackers target authentication sessions, cookies, and OAuth tokens rather than relying solely on password theft. By obtaining valid authentication artifacts, attackers can access Microsoft 365 environments while bypassing conventional MFA protections.


  • The use of Evilginx-based AiTM frameworks highlights how publicly available phishing tools have evolved into effective MFA-bypass platforms. These frameworks proxy legitimate login pages, capture authenticated sessions, and allow attackers to reuse valid sessions without requiring victims’ credentials again.


  • The OAuth Device Code flow abuse represents a different attack method, in which attackers leverage a legitimate Microsoft authentication mechanism to obtain tokens after victims approve the request. This approach bypasses password theft entirely by abusing trusted authentication workflows.


  • The exposed infrastructure provided insight into attacker operations, including phishing configurations, victim tracking data, remote administration tools, and evidence of AI-assisted development. The findings demonstrate how phishing ecosystems now provide reusable tooling and automation that reduce the technical expertise required to conduct large-scale identity attacks.

Analyst Comments

These Microsoft 365 phishing campaigns demonstrate the ongoing evolution of identity-focused attacks, as adversaries increasingly target authentication sessions, tokens, and legitimate cloud authorization mechanisms to bypass traditional security controls. The combination of AiTM phishing, OAuth abuse, remote management tools, and PhaaS infrastructure enables threat actors to maintain persistent access while blending into legitimate cloud activity.

The growing availability of phishing frameworks and AI-assisted attack development highlights the need for continuous identity security improvements beyond traditional phishing defenses. Arete recommends that organizations strengthen identity monitoring, adopt phishing-resistant MFA where possible, review OAuth application permissions, monitor token activity, and implement conditional access policies to detect and restrict suspicious Microsoft 365 authentication behavior. Security teams should also monitor post-compromise indicators such as abnormal mailbox access, suspicious application consent, unauthorized remote tools, and unusual sign-in activity.

Sources

  • One Misconfigured Server, Three Active Campaigns: Full exposure of three AiTM Phishing Operators

  • Misconfigured Server Reveals Three Evilginx Phishing Operations Targeting Microsoft 365

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Helix Extortion Group Debuts in SharePoint Data Theft Attacks

A newly identified data-extortion group, Helix, is reportedly conducting targeted campaigns by exploiting identity-based attack techniques to gain access to Microsoft 365 environments and exfiltrate data from SharePoint Online. The group leverages voice phishing (vishing), device code phishing, and multi-factor authentication (MFA) abuse to compromise user accounts and establish unauthorized access. 

  • Helix threat actors reportedly initiate intrusions through vishing campaigns, impersonating trusted individuals—often the target's manager—and leveraging caller ID spoofing to enhance credibility. 


  • The actors then attempt to persuade victims to complete device code phishing workflows, enabling unauthorized access to corporate accounts and Microsoft 365 resources. 


  • Following successful authentication, the actors conduct reconnaissance and enumeration of SharePoint environments before identifying and exfiltrating sensitive data for extortion purposes. 


  • Helix's variable dwell times suggest a flexible, target-specific operational approach, enabling the group to adapt its intrusion timeline to victim environments to maximize data theft and extortion opportunities while minimizing the likelihood of detection. Helix's operations also appear to be focused on large-scale data theft and extortion, with an emphasis on automated SharePoint data exfiltration following successful credential or session compromise.

Overlaps with Other Extortion Groups

Researchers assess that Helix likely emerged from or has operational overlap with the ShinyHunters and BlackFile/Redact cybercriminal ecosystems. ShinyHunters historically focuses on compromising websites, developer repositories, and exposed credentials or API keys to gain access to corporate cloud environments, monetizing stolen victim data on the dark web. BlackFile utilizes identity-centric and social engineering–driven methods of intrusion, relying less on traditional malware and instead leveraging credential theft, privilege escalation, rapid data exfiltration, and coercive tactics such as swatting to maximize extortion pressure. In May 2026, BlackFile announced that it would be rebranding as “Redact” (which may have later rebranded again to “Pink”), yet despite the rebrands, threat actors operating within these groups continued to exhibit similar operational models, victimology, and extortion methodologies.  

Analyst Comments

Collectively, the similarities between the groups suggest the possibility of a shared criminal ecosystem, affiliate network, or loosely connected threat cluster rather than entirely independent operations.  The emergence of Helix further reflects the broader trend of extortion groups rebranding or fragmenting while retaining proven attack techniques and operational infrastructure to support their criminal activities. Despite suspicion of these groups’ connectivity, the exact nature of the relationship remains unconfirmed.  As Helix focuses on identity-based attack techniques to gain access to Microsoft 365 environments, Arete recommends that organizations remain vigilant in using MFA, enforcing strong identity security controls, continuously monitoring authentication activity, and enhancing user awareness of social engineering tactics.

  • Sources

  • Helix, a New Name in the Data Extortion Ecosystem?

  • BlackFile actively extorting data-theft victims in retail and hospitality sector

  • "Pink" Data Extortion Group Hunting With Evasive Phishing Kits