Defender

Overview Attribute CVE-2026-41091 CVE-2026-45498 Type Local Privilege Escalation Denial of Service Component Malware Protection Engine Antimalware Platform Affected Engine ≤ 1.1.26030.3008 Platform ≤ 4.18.26030.3011 CWE CWE-59 (Link Following) — Impact Standard user → SYSTEM Defender disabled / system unresponsive Exploit ✅ Active in the wild ✅ Active in the wild Patch Engine 1.1.26040.8 Platform 4.18.26040.7 CISA KEV ✅ Added 2026-05-20 ✅ Added 2026-05-20 FCEB Deadline June 3, 2026 June 3, 2026 Microsoft has started rolling out patches for two actively exploited zero-day vulnerabilities in Microsoft Defender. Both were added to CISA’s Known Exploited Vulnerabilities (KEV) catalog on May 20, with federal agencies ordered to patch within two weeks. ...

Windows Defender Is the Target Now This week’s headline isn’t about some exotic exploit kit. It’s about the security tool itself getting owned. Three zero-days targeting Microsoft Defender — BlueHammer, RedSun, and UnDefend — have shifted from proof-of-concept to active in-the-wild exploitation. All three come from the same researcher (Nightmare-Eclipse / Chaotic Eclipse), who released exploit code publicly in protest over Microsoft’s handling of the disclosure process. Huntress Labs has confirmed hands-on-keyboard attackers combining these with compromised SSL VPN credentials for real intrusions. ...

Overview Same researcher, same target, new weapon. Nightmare-Eclipse — the security researcher behind the BlueHammer Windows Defender LPE zero-day — has released UnDefend, a tool that can completely disable Windows Defender from a standard user account with no administrative privileges. Where BlueHammer escalates privileges through Defender, UnDefend simply kills Defender’s ability to protect you — and does it without needing admin rights at all. Attribute Value Tool UnDefend Author Nightmare-Eclipse (Chaotic Eclipse) Repository github.com/Nightmare-Eclipse/UnDefend Language C++ License MIT Stars 32 (as of Apr 13, 2026) Requires Admin ❌ No CVE Pending / Not assigned Patch ❌ None Related BlueHammer (LPE zero-day, same researcher) How It Works UnDefend operates in two modes: ...

Overview Attribute Value CVE ID CVE-2026-33825 CVSS Score 7.8 Vendor Microsoft Product Windows Defender Antivirus (Windows 10/11, Server 2016+) Vulnerability Type TOCTOU + Path Confusion → Local Privilege Escalation Status ✅ Patched (April 14, 2026 Patch Tuesday) CWE CWE-367 (Time-of-check Time-of-use Race Condition) KEV Added Not yet Exploitation Status ⚠️ PoC public, no confirmed in-the-wild attacks yet Patch Status ❌ Unpatched (as of April 12, 2026) Affected Versions Version Status Windows 10 (1709+) ❌ Vulnerable Windows 11 ❌ Vulnerable Windows Server 2016+ ⚠️ Partial (elevated admin, not full SYSTEM) Windows 10 (pre-1709) ✅ Not affected (no Cloud Files API) Description BlueHammer is a local privilege escalation vulnerability in Microsoft Defender Antivirus that chains a TOCTOU race condition with path confusion in Defender’s signature update workflow. A standard user can exploit Defender’s own privileged update mechanism to leak the SAM hive, decrypt credentials, and achieve SYSTEM privileges. ...

It’s been nine days since Chaotic Eclipse published the BlueHammer exploit on GitHub. Here’s what’s changed — and what hasn’t. Current Status: Still Zero-Day Attribute Status CVE Assigned ❌ No Microsoft Patch ❌ None Official Mitigation ❌ None PoC Available ✅ Original + Reimplementation Actively Exploited ⚠️ No confirmed in-the-wild attacks (yet) Detection Coverage 8/72 vendors on VirusTotal Microsoft’s last public statement (April 7) reaffirmed commitment to coordinated disclosure without addressing the MSRC communication breakdown or providing a timeline. ...

Since my initial coverage of BlueHammer, the security community has produced excellent technical analysis. This post consolidates the deep-dive details you need to understand how this exploit actually works — and why it’s more sophisticated than most LPEs. The Big Picture BlueHammer isn’t your typical privilege escalation. It doesn’t exploit a single bug — it chains seven distinct stages, weaponizing Windows Defender’s own trusted update mechanism against the system. Key insight: The exploit abuses Defender’s signature update workflow to leak the SAM hive, decrypt credentials, and achieve SYSTEM — all from a standard user context. ...