Wind Up for Windows Users: Three Zero-Day Attacks On The Loose
Title: Urgent Alert: Three Unknown Vulnerabilities Threaten Microsoft Windows Users
It's another stressful one for Windows users, what with the upcoming end of security support for Windows 10 and the rise of Russian cyberattacks. Now, to top it all off, Microsoft has announced that three uncovered vulnerabilities are currently in play in ongoing cyberattacks. Let's break it down for you.
High Alert for All Windows Users: Three Zero-Day Attacks In Progress
Microsoft has dropped its latest Patch Tuesday bundle, and it's a hefty one: a whopping 159 vulnerabilities, twelve of them critical, including no less than eight zero-day exploits. Among them, three have already been spotted in the wild, as per Microsoft. "This is one of those months where admins need to take a step back, breathe deeply, and plan their approach," said Tyler Reguly, associate director of security research and development at Fortra.
Sadly, the technical specifics on these zero-day attacks are still scarce. They are named CVE-2025-21335, CVE-2025-21333, and CVE-2025-21334, and they impact Hyper-V — a critical component in modern Windows 11 operating systems, used for tasks like device guard and credential guard. These bugs allow attackers to exploit any access already gained through methods like phishing, escalating their privileges to full system control.
Microsoft hasn't yet commented on the matter.
The Potential Impact of Windows Zero-Day Triple Threat
As Mike Walters, president and co-founder of Action1, warned, these zero-day exploits pose significant threats to Windows users, particularly those relying on Hyper-V, including data centers, cloud providers, enterprise IT environments, and development platforms. Potential consequences involve:
- Manipulating virtual machine access on the host.
- Stealing sensitive data or credentials.
- Moving horizontally within the network to target additional systems.
- Disrupting critical services by tampering with configurations or deploying malicious code.
Given the ongoing exploitation, Walters suggests that users prioritize applying the available security updates. Further, organizations should bolster their security measures, recommending measures like restricting local access, enforcing strong authentication, and segmenting critical systems.
[1] CVE-2025-21333 [2] CVE-2025-21334 [3] CVE-2025-21335 [4] Enrichment Data
Sources
Enrichment Data
Overall:
The trio of actively exploited zero-day vulnerabilities impacting Hyper-V in Windows 10, 11, and Server 2025 are:
- CVE-2025-21333: A buffer overflow bug that allows attackers to elevate privileges to SYSTEM on compromised Windows and Windows Server machines, affecting the Windows Hyper-V's NT Kernel.
- CVE-2025-21334: A use-after-free flaw that allows attackers to gain elevated privileges to SYSTEM, impacting the Hyper-V component of the Windows NT Kernel.
- CVE-2025-21335: Another use-after-free flaw that allows attackers to gain elevated privileges to SYSTEM, impacting the Hyper-V component of the Windows NT Kernel.
Implications
- Privilege Escalation: These vulnerabilities allow attackers to execute code with SYSTEM privileges, even with low-level access, potentially leading to significant security risks.
- Potential Impacts: Exploitation of these vulnerabilities could result in accessing and manipulating virtual machines, stealing sensitive data or credentials, moving horizontally within the network, and disrupting critical services by modifying configurations or deploying malicious code.
- Severity Rating: These vulnerabilities are rated Important with a CVSS score of 7.8, indicating a high severity level.
- Affected Systems: These vulnerabilities affect Windows 10, Windows 11, and all supported versions of Windows Server, including Windows Server 2022 and 2025.
- Source: CVE-2025-21333, CVE-2025-21334, and CVE-2025-21335
Sources
Sources
- CVE-2025-21333: source
- CVE-2025-21334: source
- CVE-2025-21335: source
- Author: @JBunce
- Microsoft has warned Windows users about three zero-day vulnerabilities being exploited in ongoing cyberattacks, which were spotted in the wild after Microsoft's latest Patch Tuesday bundle.
- These zero-day exploits, named CVE-2025-21333, CVE-2025-21334, and CVE-2025-21335, impact Hyper-V, a critical component in modern Windows operating systems.
- A Windows hack using these vulnerabilities allows attackers to escalate their privileges, gaining full system control once they have obtained initial access through methods like phishing.
- Microsoft security warning advises users to prioritize applying security updates and recommends strengthening security measures, such as restricting local access, enforcing strong authentication, and segmenting critical systems.
- These zero-day attacks, classified as a Windows zero-day triple threat, are significant threats to Windows users, particularly those relying on Hyper-V, potentially leading to manipulating virtual machine access, stealing sensitive data or credentials, and disrupting critical services.