An extensive account takeover (ATO) campaign targeting Microsoft Entra ID has been identified by cybersecurity experts, exploiting a powerful open-source penetration testing framework known as TeamFiltration. 

First detected in December 2024, the campaign has accelerated rapidly, compromising more than 80,000 user accounts across many cloud environments over the past several years. It is a sophisticated and stealthy attack operation aimed at breaching enterprise cloud infrastructure that has been identified by the threat intelligence firm Proofpoint with the codename UNK_SneakyStrike, a sophisticated and stealthy attack operation. 

UNK_SneakyStrike stands out due to its distinctive operational pattern, which tends to unfold in waves of activity throughout a single cloud environment often targeting a broad spectrum of users. The attacks usually follow a period of silent periods lasting between four and five days following these aggressive bursts of login attempts, a tactic that enables attackers to avoid triggering traditional detection mechanisms while maintaining sustained pressure on organizations' defence systems. 

Several technical indicators indicate that the attackers are using TeamFiltration—a sophisticated, open-source penetration testing framework first introduced at the Def Con security conference in 2022—a framework that is highly sophisticated and open source. As well as its original purpose of offering security testing and red teaming services in enterprises, TeamFiltration is now being used by malicious actors to automate large-scale user enumeration, password spraying, and stealthy data exfiltration, all of which are carried out on a massive scale by malicious actors. 

To simulate real-world account takeover scenarios in Microsoft cloud environments, this tool has been designed to compromise Microsoft Entra ID, also known as Azure Active Directory, in an attempt to compromise these accounts. It is important to know that TeamFiltration's most dangerous feature is its integration with the Microsoft Teams APIs, along with its use of Amazon Web Services (AWS) cloud infrastructure to rotate the source IP addresses dynamically. 

Not only will this strategy allow security teams to evade geofencing and rate-limiting defences, but also make attribution and traffic filtering a significant deal more challenging. Additionally, the framework features advanced functionalities that include the ability to backdoor OneDrive accounts so that attackers can gain prolonged, covert access to compromised systems without triggering immediate alarms, which is the main benefit of this framework. 

A combination of these features makes TeamFiltration a useful tool for long-term intrusion campaigns as it enhances an attacker's ability to keep persistence within targeted networks and to siphon sensitive data for extended periods of time. By analysing a series of distinctive digital fingerprints that were discovered during forensic analysis, Proofpoint was able to pinpoint both the TeamFiltration framework and the threat actor dubbed UNK_SneakyStrike as being responsible for this malicious activity. 

As a result, there were numerous issues with the tool, including a rarely observed user agent string, hardcoded client identifications for OAuth, and a snapshot of the Secureworks FOCI project embedded within its backend architecture that had been around for quite some time. As a result of these technical artefacts, researchers were able to trace the attack's origin and misuse of tools with a high degree of confidence, enabling them to trace the campaign's origin and tool misuse with greater certainty. 

An in-depth investigation of the attack revealed that the attackers were obfuscating and circumventing geo-based blocking mechanisms by using Amazon Web Services (AWS) infrastructure spanning multiple international regions in order to conceal their real location. A particularly stealthy manoeuvre was used by the threat actors when they interacted with the Microsoft Teams API using a "sacrificial" Microsoft Office 365 Business Basic account, which gave them the opportunity to conduct covert account enumeration activities. 

Through this tactic, they were able to verify existing Entra ID accounts without triggering security alerts, thereby silently creating a map of user credentials that were available. As a result of the analysis of network telemetry, the majority of malicious traffic originated in the United States (42%). Additional significant activity was traced to Ireland (11%) and the United Kingdom (8%) as well. As a consequence of the global distribution of attack sources, attribution became even more complex and time-consuming, compromising the ability to respond efficiently. 

A detailed advisory issued by Proofpoint, in response to the campaign, urged organisations, particularly those that rely on Microsoft Entra ID for cloud identity management and remote access-to initiate immediate mitigations or improvements to the system. As part of its recommendations, the TeamFiltration-specific user-agent strings should be flagged by detection rules, and multi-factor authentication (MFA) should be enforced uniformly across all user roles, based on all IP addresses that are listed in the published indicators of compromise (IOCs). 

It is also recommended that organisations comply with OAuth 2.0 security standards and implement granular conditional access policies within Entra ID environments to limit potential exposure to hackers. There has been no official security bulletin issued by Microsoft concerning this specific threat, but internal reports have revealed that multiple instances of unauthorised access involving enterprise accounts have been reported. This incident serves as a reminder of the risks associated with dual-use red-teaming tools such as TeamFiltration, which can pose a serious risk to organisations. 

There is no doubt in my mind that such frameworks are designed to provide legitimate security assessments, however, as they are made available to the general public, they continue to raise concerns as they make it more easy for threat actors to use them to gain an advantage, blurring the line between offensive research and actual attack vectors as threats evolve. 

The attackers during the incident exploited the infrastructure of Amazon Web Services (AWS), but Amazon Web Services (AWS) reiterated its strong commitment to promoting responsible and lawful use of its cloud platform. As stated by Amazon Web Services, in order to use its resources lawfully and legally, all customers are required to adhere to all applicable laws and to adhere to the platform's terms of service. 

A spokesperson for Amazon Web Services explained that the company maintains a clearly defined policy framework that prevents misappropriation of its infrastructure. As soon as a company receives credible reports that indicate a potential violation of these policies, it initiates an internal investigation and takes appropriate action, such as disabling access to content that is deemed to be violating the company's terms. As part of this commitment, Amazon Web Services actively supports and values the global community of security researchers. 

Using the UNK_SneakyStrike codename, the campaign has been classified as a highly orchestrated and large-scale operation that is based on the enumeration of users and password spraying. According to researchers at Proofpoint, these attempts to gain access to cloud computing services usually take place in bursts that are intense and short-lived, resulting in a flood of credentials-based login requests to cloud environments. Then, there is a period of quietness lasting between four and five days after these attacks, which is an intentional way to prevent continuous detection and prolong the life cycle of the campaign while enabling threat actors to remain evasive. 

A key concern with this operation is the precision with which it targets its targets, which makes it particularly concerning. In the opinion of Proofpoint, attackers are trying to gain access to nearly all user accounts within the small cloud tenants, while selectively targeting particular users within the larger enterprise environments. 

TeamFiltration's built-in filtering capabilities, which allow attackers to prioritise the highest value accounts while avoiding detection by excessive probing, are a calculated approach that mirrors the built-in filtering capabilities of TeamFiltration. This situation underscores one of the major challenges the cybersecurity community faces today: tools like TeamFiltration that were designed to help defenders simulate real-world attacks are increasingly being turned against organisations, instead of helping them fight back. 

By weaponizing these tools, threat actors can infiltrate cloud infrastructure, extract sensitive data, establish long-term access, and bypass conventional security controls, while infiltrating it, extracting sensitive data, and establishing long-term control. In this campaign, we are reminded that dual-purpose cybersecurity technologies, though essential for improving organization resilience, can also pose a persistent and evolving threat when misappropriated. 

As the UNK_SneakyStrike campaign demonstrates, the modern threat landscape continues to grow in size and sophistication, which is why it is imperative that cloud security be taken into account in a proactive, intelligence-driven way. Cloud-native organisations must take steps to enhance their threat detection capabilities and go beyond just reactive measures by investing in continuous threat monitoring, behavioural analytics, and threat hunting capabilities tailored to match their environments' needs. 

In the present day, security strategies must adapt to the dynamic nature of cloud infrastructure and the growing threat of identity-based attacks, which means relying on traditional perimeter defences or static access controls will no longer be sufficient. In order to maintain security, enterprise defenders need to routinely audit their identity and access management policies, verify that integrated third-party applications are secure, and review logs for anomalies indicative of low-and-slow intrusion patterns. 

In order to build a resilient ecosystem that can withstand emerging threats, cloud service providers, vendors, and enterprise security teams need to work together in order to create a collaborative ecosystem. As an added note, cybersecurity community members must engage in ongoing discussions about how dual-purpose security tools should be distributed and governed to ensure that innovation intended to strengthen defences is not merely a weapon that compromises them, but rather a means of strengthening those defences. 

The ability to deal with advanced threats requires agility, visibility, and collaboration in order for organisations to remain resilient. There is no doubt that organisations are more vulnerable to attacks than they were in the past, but they can minimise exposure, contain intrusions quickly, and ensure business continuity despite increasingly coordinated, deceptive attack campaigns if they are making use of holistic security hygiene and adopting a zero-trust architecture.