A cybersecurity researcher known as MSNightmare has released a new proof of concept called ShieldCrash, which allows an attacker to access protected files with SYSTEM privileges on Windows, even after Microsoft issued a patch to address a previous vulnerability called ShieldBreak (CVE-2026-69414). SYSTEM is the highest level of access on a Windows system, surpassing even administrator rights. While Microsoft patched ShieldBreak in its protection engine, MSNightmare claims that ShieldCrash can bypass this fix on machines updated with the September 2026 Patch Tuesday update. However, this exploit does not enable file writing, only the reading of protected files. ShieldCrash was uploaded to GitHub, where it is described as a "proof of concept skeleton" by the researcher. MSNightmare has been actively disclosing vulnerabilities in Microsoft products since April 2026, including BlueHammer, RedSun, UnDefend, and YellowKey. These vulnerabilities allowed attackers to gain SYSTEM access or disable Defender, Microsoft’s built-in security software. Some of these flaws were reportedly used in real-world attacks before patches were issued. For example, the RoguePlanet vulnerability, rated 7.8 on the CVSS scale, exploited a flaw in Defender’s synchronization process to replace legitimate files with malicious ones. Microsoft issued an out-of-cycle update in early July to address this. The researcher’s ongoing conflict with Microsoft began after he reported multiple vulnerabilities, leading to a public dispute over how the company handles such disclosures. In May 2026, Microsoft introduced a new Digital Crimes Unit in a blog post, a move interpreted by some in the cybersecurity community as a warning about potential legal consequences for uncoordinated vulnerability disclosures. Katie Moussouris, who created Microsoft’s first bug bounty program, warned that such a statement might deter researchers from sharing their findings. Although a Microsoft spokesperson later clarified the company’s position on social media, the original blog post remains unchanged. MSNightmare has limited the scope of ShieldCrash, noting that it requires local access to the machine, such as through a compromised user account or an already installed malicious program. The exploit does not allow file writing or execution, only the extraction of protected files on Windows systems with the updated protection engine. Microsoft has not yet officially responded to the release of ShieldCrash, and the researcher admits that the tool is not yet fully developed, citing a lack of immediate motivation to expand on it.