--- title: SignDrop: a Windows zero-day that turns Defender into a... description: A new Windows zero-day called SignDrop lets a local user with ordinary rights escalate to full SYSTEM privileges. Disclosed by Abdelhamid Naceri (Nightmare... canonical: https://daily.dev/posts/signdrop-a-windows-zero-day-that-turns-defender-into-a-path-to-system-emchtqqhe twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: SignDrop: a Windows zero-day that turns Defender into a path to SYSTEM | daily.dev og:description: A new Windows zero-day called SignDrop lets a local user with ordinary rights escalate to full SYSTEM privileges. Disclosed by Abdelhamid Naceri (Nightmare... og:url: https://daily.dev/posts/signdrop-a-windows-zero-day-that-turns-defender-into-a-path-to-system-emchtqqhe og:image: https://api.daily.dev/og/posts/emchTqqhe.png og:image:alt: SignDrop: a Windows zero-day that turns Defender into a path to SYSTEM og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # SignDrop: a Windows zero-day that turns Defender into a path to SYSTEM **[Collections](https://daily.dev/sources/collections)** · 2 min read · 3 upvotes · 2 comments ## Summary A new Windows zero-day called SignDrop lets a local user with ordinary rights escalate to full SYSTEM privileges. Disclosed by Abdelhamid Naceri (Nightmare Eclipse), it abuses a CLFS mitigation Microsoft added in October 2025 by tricking Windows Defender into creating a file with SYSTEM-level access. Naceri says the same technique can bypass tamper protection in any antivirus or EDR product, not just Defender. He tested it on Windows 11 26H2, 26H2 Experimental, and Windows Server 2025 Experimental, and estimates about 80% of Windows installs are vulnerable. ## Content A new Windows zero-day called SignDrop lets a local user with ordinary rights get full SYSTEM privileges. It was disclosed by Abdelhamid Naceri, who goes by Nightmare Eclipse, and it works by abusing a mitigation Microsoft added to the Common Log File System (CLFS) in October 2025. That mitigation was meant to head off attacks on other CLFS vulnerabilities. ## How the exploit works The attack tricks a privileged process, in this case Windows Defender, into doing the dirty work. 1. The attacker calls `ServerMpUpdateEngineSignature`, a legitimate Defender function used for signature updates. 2. Using Windows Object Manager symbolic links, the attacker makes Defender open a crafted CLFS container in the security context of the antimalware engine. 3. If the container's associated authentication file is missing, CLFS creates it using Defender's SYSTEM privileges. 4. CLFS gives the new file the permissions of the original file, so the attacker can end up with access to a file created at SYSTEM level. Naceri says the same trick can bypass tamper protection in any antivirus or EDR product, not just Defender. ## Scope Naceri tested SignDrop on Windows 11 26H2, 26H2 Experimental, and Windows Server 2025 Experimental. He estimates that about 80% of Windows installs are vulnerable. ## What defenders can do There is no fix yet beyond waiting for a Microsoft patch. Turning off the CLFS mitigation isn't a real workaround, since that would expose devices to the memory corruption attacks it was built to stop. That is the irony here: a defensive measure created the opening. Microsoft hasn't yet published a patch for SignDrop. ## Questions this post answers ### What is the SignDrop Windows zero-day vulnerability and how does it work? SignDrop is a local privilege escalation exploit that lets a standard user gain SYSTEM access on Windows by abusing a CLFS mitigation Microsoft added in October 2025. It tricks Windows Defender's ServerMpUpdateEngineSignature function, using Object Manager symbolic links, into creating a file at SYSTEM privilege that the attacker then controls. Disclosed by Abdelhamid Naceri (Nightmare Eclipse). _Security teams tracking active Windows privilege escalation exploits can follow coverage like this on daily.dev._ ### Which Windows versions are affected by the SignDrop CLFS privilege escalation exploit? SignDrop was tested and confirmed on Windows 11 26H2, 26H2 Experimental, and Windows Server 2025 Experimental. The researcher who disclosed it, Abdelhamid Naceri, estimates roughly 80% of Windows installations are vulnerable. No Microsoft patch has been released yet. _Admins deciding how urgently to respond to unpatched Windows flaws can track updates on daily.dev._ ### Is disabling the CLFS mitigation a valid workaround for the SignDrop vulnerability? No, turning off the CLFS mitigation is not a safe workaround for SignDrop. Doing so would expose devices to the memory corruption attacks that mitigation was originally built to prevent, since the mitigation itself is what SignDrop abuses. There is currently no fix beyond waiting for a Microsoft patch. _Those weighing mitigation trade-offs for unpatched Windows CVEs can follow developments on daily.dev._ ## Community discussion Top comments from developers on daily.dev. **@embolex** · 0 upvotes > Doesnt matter anyways. At least not in Germany where the goverment makes laws to hack into system by law and being allowed to not only bypass security mechanisms, they also want to allow to delete, create and manipulate data on systems, in specific cases. > > So who cares about an security leak in Windows ..... **@petecapecod** · 0 upvotes > great, just great. I'm tired boss ## Similar posts on daily.dev - [Nightmare-Eclipse Strikes Again with 'ShieldCrash' Windows Exploit](https://daily.dev/posts/nightmare-eclipse-strikes-again-with-shieldcrash-windows-exploit-3pp4wzefx) · Dark Reading · 0 upvotes · 0 comments - [New Microsoft Defender “RedSun” zero-day PoC grants SYSTEM privileges](https://daily.dev/posts/new-microsoft-defender-redsun-zero-day-poc-grants-system-privileges-uwklow0f7) · BleepingComputer · 1 upvotes · 0 comments --- Tags: [#windows](https://daily.dev/tags/windows), [#zero-day](https://daily.dev/tags/zero-day) [View this post on daily.dev](https://daily.dev/posts/signdrop-a-windows-zero-day-that-turns-defender-into-a-path-to-system-emchtqqhe) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"SignDrop: a Windows zero-day that turns Defender into a path to SYSTEM","url":"https://daily.dev/posts/signdrop-a-windows-zero-day-that-turns-defender-into-a-path-to-system-emchtqqhe","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/signdrop-a-windows-zero-day-that-turns-defender-into-a-path-to-system-emchtqqhe"},"datePublished":"2026-11-13T16:58:41.031Z","dateModified":"2026-11-13T16:59:21.997Z","description":"A new Windows zero-day called SignDrop lets a local user with ordinary rights escalate to full SYSTEM privileges. 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At least not in Germany where the goverment makes laws to hack into system by law and being allowed to not only bypass security mechanisms, they also want to allow to delete, create and manipulate data on systems, in specific cases.\nSo who cares about an security leak in Windows …","datePublished":"2026-11-13T21:31:02.599Z","url":"https://daily.dev/posts/emchTqqhe#c-XpehYuwi4","author":{"@type":"Person","name":"Rick Kühnreich","url":"https://daily.dev/embolex","image":"https://lh3.googleusercontent.com/a/ACg8ocKzkJ-AWviyiaUvwEgbhxs3SvNBMQCr-79WI8IELYMnVess9A=s96-c"}},{"@type":"Comment","text":"great, just great. I’m tired boss","datePublished":"2026-11-14T13:45:44.105Z","url":"https://daily.dev/posts/emchTqqhe#c-oMTZA8tEb","author":{"@type":"Person","name":"Peter Cruckshank","url":"https://daily.dev/petecapecod","image":"https://media.daily.dev/image/upload/s--ZJhQyKws--/f_auto/v1721235024/avatars/avatar_A9xh33q0QoxtkGoJRCosp"}}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/signdrop-a-windows-zero-day-that-turns-defender-into-a-path-to-system-emchtqqhe#faq","mainEntity":[{"@type":"Question","name":"What is the SignDrop Windows zero-day vulnerability and how does it work?","acceptedAnswer":{"@type":"Answer","text":"SignDrop is a local privilege escalation exploit that lets a standard user gain SYSTEM access on Windows by abusing a CLFS mitigation Microsoft added in October 2025. It tricks Windows Defender's ServerMpUpdateEngineSignature function, using Object Manager symbolic links, into creating a file at SYSTEM privilege that the attacker then controls. 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