Windows Defender Patch for RoguePlanet Zero-Day Vulnerability May Exhaust Disk Space on Windows Systems
Microsoft has issued a patch for a critical zero-day vulnerability known as RoguePlanet (CVE-2026-50656) affecting the Microsoft Malware Protection Engine that powers Windows Defender. However, security researcher NightmareEclipse, who originally discovered and disclosed the flaw, warns that the fix itself may cause Windows systems to exhaust all available disk space by writing massive files to the drive.
The vulnerability first gained attention in June when NightmareEclipse published technical details and a working exploit. According to the researcher, RoguePlanet enabled remote attackers to obtain full administrative control over both Windows 10 and Windows 11 even when real-time protection was turned off. In response, Microsoft released an update to the Microsoft Malware Protection Engine component, which is designed to install automatically without requiring user intervention. The company also added additional defensive measures alongside the fix.
Shortly after the patch deployment, NightmareEclipse reported that the update can trigger unintended behavior in which Defender writes enormous volumes of data to disk. The issue is linked to the mpengine.dll library and the SpyNet functions that attempt to locally cache the Zone.Identifier alternate data stream — a Windows metadata mechanism used to track file origin information such as downloads from the internet.
Under normal circumstances, Windows Defender enforces strict size limits on files it creates during scanning and quarantine operations. However, the researcher claims that Zone.Identifier streams are treated as an exception, allowing Defender to store them locally regardless of their size. An attacker can exploit this by setting up a specially crafted SMB server that delivers a malicious file accompanied by an extremely large Zone.Identifier stream while keeping the connection alive. This can cause Defender to hang during processing and consume all remaining free space on the system drive.
While the computer may not crash immediately, a Windows system with a completely full disk tends to exhibit erratic behavior: applications and system services may fail unpredictably, similar to an overloaded server. Microsoft has not yet confirmed or commented on the reported disk-exhaustion issue at the time of publication. The ongoing dispute between the company and NightmareEclipse has lasted several months, with the researcher criticizing Microsoft for inadequate recognition and compensation for discovered vulnerabilities, while the company has expressed concerns about the early public disclosure of exploits before patches were available.
Related articles
Security Week 2644: Active Exploitation of PHP2Shell Vulnerabilities Confirmed
PHP developers released patches for two critical vulnerabilities collectively known as PHP2Shell on October 20, affecting PHP 8.2 through 8.5 as well as older branches. The flaws allow unauthenticated remote code execution on affected servers, which power approximately 70 percent of websites. Despite expectations of immediate exploitation, confirmed attacks with working exploits only began on October 25. CrowdStrike noted technical difficulties in weaponizing the issues in real-world environments. Only one-fifth of top Russian websites had applied the fixes by October 25. Additional incidents included compromised eMudhra certificates, a critical GitLab flaw, and a 16-year-old Broadcom router vulnerability.
Positive Technologies Offers Up to 500,000 Rubles for Bypassing PT Application Firewall
Positive Technologies has expanded its Standoff Bug Bounty program to include rewards for bypassing its web application firewalls. Researchers can earn between 150,000 and 500,000 rubles for demonstrating practical bypasses against PT Application Firewall PRO and PT Application Firewall Cloud. The program targets the core protective mechanisms, including traffic filtering, attack detection rules, and the management layer used by administrators. Submissions must include reproducible attack scenarios that show how malicious requests can pass through undetected, rather than relying on scanner reports or theoretical findings. Reward amounts vary by severity and confirmed business impact, with critical issues in the PRO version paying up to 500,000 rubles. The company plans to use validated findings to strengthen detection rules and improve overall product resilience.
Tailscale SSH Vulnerability Allows Root Access via Unix Socket Redirection
A researcher identified flaws in Tailscale that let an attacker with existing SSH access on one node escalate to root privileges and move laterally across the network. Erica Windisch of Cyberdione Labs demonstrated the issues in lab conditions against Tailscale 1.104.2 and Headscale 0.29.5. The core problem stems from privileged operations performed by the tailscaled process when handling Unix socket redirection, granting an ordinary SSH session access to root-only resources. The researcher used the technique to interact with Docker and run elevated commands, and showed that broad access policies allow automated lateral movement in under a second. Additional issues include denial-of-service conditions and bypasses of certain restrictions. Recommendations include reviewing SSH policies and disabling unnecessary socket redirection, noting that Headscale 0.29.5 lacks an independent way to turn the feature off.
Critical CVE-2026-111497 Out-of-Bounds Write Flaw in Google Brotli Decoder Impacts Broad Range of Environments
A severe vulnerability has been identified in the Google-developed Brotli decoder used for decompressing data in web communications and other applications. The flaw, tracked as CVE-2026-111497, allows out-of-bounds writes when processing specially crafted compressed data, potentially enabling arbitrary code execution, information disclosure, or denial of service. It carries a CVSS v4.0 base score of 9.2 and is rated Critical. Google has released patched versions 1.2.1, 1.1.1, and 1.0.10 of the library. Node.js incorporated the fix in its updates, while Microsoft issued an out-of-band patch for .NET on October 25, 2026, to address the issue. The vulnerability affects any environment relying on the Brotli C implementation for data decompression.