Disgruntled Researcher Discloses New Zero-Day in Windows Antivirus
A disgruntled security researcher has disclosed a new zero-day vulnerability in Windows Defender, which could allow attackers to elevate their privileges to the highest system level. The vulnerability, called ShieldBreak, was announced by the researcher, Nightmare Eclipse, who has been feuding with Microsoft. The researcher has released a proof-of-concept code to demonstrate the vulnerability, which has been tested by other security researchers and found to work.
- ▪The ShieldBreak vulnerability is a zero-day flaw that can be used to elevate privileges to the highest system level.
- ▪The vulnerability can only be exploited by an attacker who already has access to the system, and it cannot be used for remote hacking.
- ▪Nightmare Eclipse has released a proof-of-concept code to demonstrate the vulnerability, which has been tested by other security researchers.
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| Original publisher | PCMag |
| Canonical URL | https://www.pcmag.com/news/disgruntled-researcher-discloses-new-zero-day-in-windows-antivirus |
| Publication time | Wed, 12 Aug 26 16:36:15 +0000 |
| Retrieval time | 2026-08-12T16:41:31.558Z |
| Last seen | 2026-08-12T16:41:31.558Z |
| Headline source | Publisher (no WeSearch rewrite) |
| Excerpt source | publisher body |
| Excerpt method | First ~120 words (~800 chars) of extracted publisher body, fair-use limited. |
| Summary | WeSearch · cerebras-chat (WeSearch summarizer) |
| Summary source text | contentText |
| Citation coverage | Summary is a WeSearch-generated derivative; primary citation is the original publisher URL. |
| Cluster | STdDF-RpcXSy · 1 stories |
| Cluster logic | Grouped by semantic title/content similarity across sources within a rolling window. Same-publisher template collisions are excluded from coverage comparison. |
| Ranking reason | Story pages are not engagement-ranked. Hub feeds use recency, with optional source-diversified chronological ordering (cap consecutive stories per source). No personalized ranking. |
| Publisher visit | Yes — open original |
| Substitutes article? | No — link-out required for full text |
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| Snippet | May a short excerpt of the publisher's text be shown? | Allowed |
| AI summary | May WeSearch generate its own short summary of the article? | Limited |
| Retrieval / RAG | May the content be exposed for third-party retrieval-augmented generation? | Not asserted |
| Model training | May the content be used to train AI models? | Not asserted |
| Commercial reuse | May the content be reused commercially? | Not permitted |
Basis: Derived from the published RSS/Atom feed. Contact: [email protected]. Reviewed: 2026-07-24.
Opening excerpt (first ~120 words) tap to expand
A disgruntled security researcher who's been feuding with Microsoft has released a newly discovered vulnerability in Windows Defender that could be used to help hackers attack PCs. On Tuesday, the researcher, Nightmare Eclipse, announced “ShieldBreak,” describing it as a zero-day vulnerability, or a flaw that currently has no software patch. The vulnerability can’t remotely hack a Windows PC; instead, it can let an attacker who already has access elevate their privileges to the highest “system” level.To prove the threat is real, Nightmare Eclipse has released a proof-of-concept code that can exploit the bug in Windows Defender in Windows 11 25H2 and Windows Server 2025.
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Excerpt limited to ~120 words for fair-use compliance. The full article is at PCMag.
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