Defender: A researcher claims that the ShieldBreak patch leaves an exploitable vulnerability
A cybersecurity researcher known as Nightmare Eclipse claims that a vulnerability in Microsoft Defender remains exploitable even after a Microsoft patch. According to him, the issue can allow attackers to gain system privileges on Windows devices that are already up to date. The company has not responded to this new discovery, as reported by 01net.
A flaw that the researcher believes is still present
In an article published on September 10, 2026, 01net reported that Nightmare Eclipse had identified a new vulnerability in Defender, which it named ShieldCrash. The researcher maintains that it is related to ShieldBreak, referenced as CVE-2026-69414, which Microsoft was supposed to have patched.
According to his analysis, the problem is not limited to arbitrary file reading. It could allow privilege escalation to the system level on devices running Windows 10, Windows 11, or Windows Server, even fully updated ones. The researcher specifies, however, that the vulnerability would not grant write access to the affected systems.
Nightmare Eclipse claims that Microsoft has patched certain elements to prevent the re-exploitation of ShieldBreak, but that a vulnerability remains under certain conditions. These are the researcher’s conclusions, as reported by 01net; the information provided does not detail the precise conditions of exploitation, nor does it constitute confirmation from Microsoft.
A disclo amid tensions
The discovery comes after the September 2026 Patch Tuesday security updates. According to 01net, Microsoft patched nearly 1,000 vulnerabilities in Windows during this update. However, the publication of this figure alone does not determine whether the vulnerability reported by Nightmare Eclipse was included in these patches or if it was discovered subsequently.
Relations between the researcher and Microsoft were already strained. In May 2026, the company criticized the disclo of vulnerabilities that had not been previously reported to it, arguing that they could expose its customers to risks. In June, it stated that it would cooperate with law enforcement if someone broke the law and caused real harm to its customers.
These stances are partly linked to the work of Nightmare Eclipse. The researcher notably reported the YellowKey vulnerability in May 2026. He also claims that Microsoft deleted the account he used with the Microsoft Security Response Center (MSRC) to submit vulnerability reports.
At this stage, the reported information is based on the researcher’s claims. The available information does not specify whether Microsoft has confirmed the existence of ShieldCrash, released a new patch, or advised users on what meas to take.
Source: cybersecurity (www.01net.com)
Original article: See the original source
Author: Jérémy Olcina
