Security researcher Nightmare Eclipse shared with the public the details of a new vulnerability that affects current versions of Windows and allows attackers to gain high privileges throughout the system. The vulnerability, called ShieldBreak, exploits a weakness in Microsoft Defender, which is built into Windows. In a successful attack, a user account with low privileges can gain full access to the device and data. According to the researcher, the vulnerability works on Windows 10 and Windows 11, as well as Windows 11 25H2 and Windows Server 2025. While Microsoft stated that it is examining the claims, it has not yet released a security update for ShieldBreak.
Nightmare Eclipse has released its proof-of-concept code for ShieldBreak in the form of an executable Windows application. This method requires the application in question to be run by the user in order for the attack to occur; Therefore, the vulnerability alone does not allow the device to be compromised remotely and without user interaction. Despite this, the ability to increase authorization through a vulnerability in Windows Defender after the application is run poses a significant risk in terms of security. Security researcher Will Dormann also independently tested the vulnerability and confirmed that the method worked. According to Dormann’s tests, Windows Defender must be active on the system for the attack to be successful.
ShieldBreak can access administrative privileges through Windows Defender
The technical method behind ShieldBreak was developed by Nightmare Eclipse. RoguePlanet It also bears traces of another vulnerability called . Microsoft had previously released a fix for RoguePlanet. However, the researcher claims that ShieldBreak was able to completely bypass this fix and that the previous measure did not completely eliminate the problem. Therefore, the new vulnerability creates controversy not only as a different security problem, but also in terms of the effectiveness of the fix that Microsoft previously applied. Since there was no patch made available to users by Microsoft at the time of ShieldBreak’s release, it is considered a zero-day vulnerability.
Microsoft stated in its statement on the subject that it was aware of the reported security vulnerability and that it was actively investigating the validity of the claims and possible usage areas. The company has not yet shared additional information about the technical details of the vulnerability, its severity or when an update will be available. Therefore, it is not yet clear how ShieldBreak will be officially classified by Microsoft. However, the fact that the proof-of-concept code is publicly available makes it possible for people with the necessary technical knowledge to examine the method. The fact that some Windows vulnerabilities disclosed by Nightmare Eclipse in the past were later used in real attacks against organizations causes the new finding to be closely monitored.
The ShieldBreak statement comes after an ongoing dispute between Nightmare Eclipse and Microsoft over reporting security vulnerabilities. The researcher claimed in various blog posts that Microsoft did not treat him appropriately and that the bug reports he submitted were not adequately addressed. According to this view, disclosing vulnerabilities to the public has become the preferred method following Microsoft’s approach to reports. In a blog post published in May, Microsoft stated that the company could take legal action against security researchers who publish zero-day vulnerabilities outside of its responsible disclosure policies. Although the company backtracked on these statements on social media following intense criticism from the security community, the original blog post remained accessible as published.
The timing of the new vulnerability is also noteworthy. ShieldBreak is Microsoft’s monthly regular Patch Tuesday It was announced just one day after the security updates were released. While the number of security problems fixed by the company in the last two-month update period reached approximately 500, it is stated that this increase is due to Microsoft’s greater use of artificial intelligence-based tools to identify security vulnerabilities. However, the ShieldBreak example shows that finding and closing many vulnerabilities with automated tools does not completely prevent existing fixes from being bypassed. On the user side, not running Windows applications of unknown origin and not delaying operating system and Defender updates are among the basic precautions that can reduce the risk.
The extent to which ShieldBreak can be used in practice will be more clearly understood after Microsoft’s technical review. While the fact that the user must run the application for the vulnerability to work limits the attack area, successful use increases the potential impact of system-wide access from a low-authorized account. A fix released by Microsoft will need to address not only the ShieldBreak method, but also the underlying mechanism that allows the protection implemented after RoguePlanet to be bypassed. For now, there is no confirmed information in the source text that the vulnerability is used in active attacks. Therefore, while current findings indicate that ShieldBreak is a local privilege escalation vulnerability that should be seriously examined, the level of risk needs to be considered together with actual attack data and Microsoft’s technical assessment.
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