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Black Kingdom Returns to Exploit Zero-Day Vulnerabilities in Unpatched Microsoft Exchange Servers

Arete Analysis

Summary

Black Kingdom ransomware recently resurfaced to target a zero-day vulnerability in Microsoft Exchange servers.

Earlier this month, Microsoft released a statement notifying the public of a zero-day exploit that affected its on-premises Exchange Servers, versions 2013 through 2019. Within a week, Arete incident responders spoke to approximately 100 affected companies — small- and medium-sized companies that had no reason to be on the target list of the Microsoft-coined hacking group Hafnium.

The worst part about this zero-day announcement was that sometime around March 10, the threat group published the proof-of-concept (PoC) code to GitHub. The irony: Microsoft owns GitHub; GitHub hosted the PoC code.  
 
Since that publication, the security community has been speculating on a second wave of attacks involving this exploit. A wave that would be worse than the first. A wave that would be linked to all sorts of corporate business interruptions from the likes of data exfiltration and ransomware.

How right was the speculation? Basically, the community #nailedit.

Second Wave of Ransomware Attacks Now Hitting

On March 12, DarkReading.com reported that a hacking group was deploying the ransomware variant,  DEARCRY!, which was affecting unpatched Microsoft Exchange Servers.  
 
Now, Arete has identified a second variant — Black Kingdom — that is also exploiting unpatched Microsoft Exchange Servers. The Black Kingdom variant made media headlines when it briefly surfaced and started to exploit the Pulse VPN zero-day in the early summer months of 2020. After, the group quietly disappeared … until this week. 

How the Black Kingdom Ransomware Group Operates

After the Black Kingdom group gains access to a network, they will perform some reconnaissance and start their encryption, leaving behind a fitting ransom note entitled decrypt_file.txt to announce their return.

Black Kingdom’s ransom note is one of the longest notes left behind by ransomware groups. It provides explicit instructions on how to contact them, the ransom amount, the Bitcoin wallet ID, and a message stating that they exfiltrated data from the network. The note also states that refusal to pay would lead them to publish the attack and stolen files on social media.

Steps you can take to help prevent unauthorized access to your network

The Microsoft Exchange vulnerability is widespread and, if like many other previously reported vulnerabilities, may not get patched automatically or quickly enough to prevent ransomware groups and any other malicious actors from gaining unauthorized access to your network.  
 
Follow these recommended steps protect your business and systems from unauthorized access: 

1. Immediately patch the Exchange Server. If the system is not or cannot be patched, disable Outlook for Web Access (OWA). If you cannot disable OWA, remove the Exchange Server from the internet.

  • Prior to running the tool, create a backup of the Exchange Server in its current state.

  • Microsoft released a One-Click Mitigation tool to patch, upgrade, and scan for malicious activity. You can find the tool on the company’s Security Center blog. 

  • Disable OWA according to the Microsoft guidelines. This may cause users to not have access to email.  

  • If you cannot patch or disable OWA, remove the system from the internet by disconnecting the network cable or powering the system down. This action will cause significant disruption and prevent users from receiving emails in certain configurations.  

 2. The U.S. Cybersecurity & Infrastructure Security Agency (CISA) issued a mitigation alert. Please read the article.

  • Block IP addresses at the firewall.

  • Enable geofencing if your organization does not conduct business outside of the United States.

3. Change passwords for all Windows-based user accounts.

  • Start with the most privileged domain administrator and service accounts, then work towards the least privileged user accounts. Also include the local administrator password.

4. Preserve any firewall, web application firewall, or VPN logs.

5. Deploy an Enterprise Detection and Response (EDR) tool throughout the environment to detect any unauthorized activity.

If you suspect any unauthorized access to your Microsoft Exchange Server or network, contact us.  

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Article

Ransomware Trends & Data Insights: July 2026

INC Ransom was the most active threat group in July, while activity remained relatively distributed among multiple threat groups, with 19 unique groups observed throughout the month. Alongside INC Ransom, Qilin, Global Secret Group, Anubis, and DragonForce rounded out the five most active threat groups observed in July. Several emerging threat actors were also observed during the month, including Booba Team, Settra, and Global Secret Group.

Figure 1. Activity from the top 3 threat groups in July 2026

 Throughout the month, analysts at Arete identified several trends behind the threat actors perpetrating cybercrime activities:

  • In July 2026, Global Secret Group emerged as a new threat actor, leveraging the leaked LockBit 3.0 (LockBit Black) source code. Although the group began operations in June 2026, it quickly accumulated a substantial number of victims on its data leak site (DLS). The group operates through TOR-based negotiation portals and qTox communications. Notably, its DLS provides step-by-step guidance on purchasing Bitcoin, including references to Coinbase and Binance, demonstrating a streamlined, victim-focused extortion process designed to simplify ransom payments.

  • Similar to Fulcrumsec, the recently emerged Settra ransomware group appears to leverage AI-driven analysis of stolen data, publishing detailed and highly structured victim reports on its DLS. Additionally, a potential EDR-disabling tool, edr_blind.exe, was identified in multiple cases, suggesting a focus on defense-evasion capabilities.

  • With the continuation of the FortiBleed campaign, researchers have now identified compromised FortiGate credentials being leveraged by both the INC and Lynx ransomware operations. Analysis revealed direct operational links between the groups, including shared ransomware infrastructure and overlap between FortiBleed victims and ransomware targets. The operators are also incorporating AI to enhance various stages of the attack lifecycle and increase operational efficiency and scale. Notably, Arete also observed an INC ransomware intrusion leveraging FortiBleed-derived access in July, reinforcing the campaign's role as a precursor to ransomware deployment.

Sources

  • Arete Internal

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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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