Microsoft has released a fix for the RoguePlanet zero‑day vulnerability, CVE‑2026‑50656, in Microsoft Defender. The update was delivered through a Malware Protection Engine patch, not via the monthly Patch Tuesday releases. Customers are advised to ensure they are running the latest engine version to receive the fix. The vulnerability was first reported in June by security researcher Nightmare Eclipse, who published technical details and proof‑of‑concept code indicating that the flaw exploits a race condition in Defender to run commands with SYSTEM privileges. According to the researcher, the exploit can succeed on some systems with a 100 percent success rate while failing on others. The researcher also said the exploit works regardless of whether Defender’s real‑time protection is enabled. Microsoft initially stated it was investigating the claims and later clarified that it had no intention of taking legal action against legitimate security research. The researcher alleged that Microsoft removed public repositories containing the exploit from GitHub and GitLab and moved the code to a self‑hosted location. With the patch applied, Microsoft has closed all zero‑days disclosed by Nightmare Eclipse earlier this year. Whether the resolution ends the dispute between Microsoft and the researcher remains uncertain.