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Nightmare Eclipse is an anonymous exploit developer and public zero-day disclosure actor focused primarily on Microsoft Windows and Microsoft Defender attack surfaces. Widely used aliases include Nightmare-Eclipse, NightmareEclipse, Chaotic Eclipse, Dead Eclipse, and MSNightmare. The actor became notable in 2026 for rapidly publishing a series of working proof-of-concept exploits and abuse techniques without coordinated disclosure, often shortly after Microsoft Patch Tuesday releases. The cluster’s releases have centered on local privilege escalation, security-feature bypass, and post-compromise abuse of trusted Windows components rather than classic memory-corruption exploitation. Publicly associated tools include BlueHammer, RedSun, UnDefend, YellowKey, GreenPlasma, MiniPlasma, RoguePlanet, GreatXML, LegacyHive, and ShieldBreak. Multiple releases specifically targeted Microsoft Defender workflows, including signature update, remediation, quarantine, and scan pipelines. Other releases targeted Windows Recovery Environment, BitLocker-related recovery paths, Windows User Profile Service behavior, and adjacent Windows security components. Observed tradecraft includes abuse of legitimate Windows mechanisms such as Volume Shadow Copy behavior, opportunistic locks, NTFS junctions and reparse points, Cloud Files APIs, Object Manager symbolic links, offline registry hive modification, scheduled task execution, and profile-loading logic. The actor’s tooling has demonstrated capabilities consistent with post-exploitation and privilege escalation from low-privileged user context to SYSTEM, as well as persistence-oriented and data-access techniques. Some releases also function as security-control evasion or degradation tooling against Microsoft Defender. Several exploits attributed to Nightmare Eclipse were described as enabling SYSTEM-level execution on supported Windows versions, including Defender-centric chains such as RedSun, RoguePlanet, and ShieldBreak. GreatXML was characterized as a BitLocker and WinRE abuse technique requiring prior administrative access and later physical access, while LegacyHive was presented as a cross-user registry hive loading primitive useful as a building block for privilege escalation or persistence. BlueHammer was associated with privileged access to sensitive registry hives and follow-on credential abuse. Public reporting also stated that some earlier Nightmare Eclipse releases were observed in real-world intrusion activity after disclosure. The actor’s dominant pattern is public release of exploit code and exploit primitives affecting Microsoft products, especially Windows Defender, with an adversarial posture toward Microsoft and no evidence in the supplied facts of ransomware operations, extortion, or financially motivated campaigns. The activity is best characterized as a disclosure-driven exploit publisher focused on exposing and operationalizing Windows security design weaknesses and privilege-boundary failures.
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Who, where, and (when attributed) which flag flies behind the operation. Pulled from open-source reporting and Mallory's analyst review.
Sectors the actor has been observed targeting.
40 distinct techniques observed across reporting, grouped by tactic. Hover any cell for the evidence excerpt; click through for MITRE's full description.
11 malware families attributed to this actor across reporting.
6 additional families tracked in Mallory.
4 CVEs this actor has used in observed campaigns. 4 of them exploited in the wild.
To date, Nightmare Eclipse released over half a dozen zero-days in Microsoft products, including BlueHammer, RedSun, and UnDefend, which have been exploited in attacks...
RedSun CVE-2026-41091 Microsoft Defender Local privilege escalation through link-following behavior Fixed in engine versions at or above 1.1.26040.8; listed in CISA KEV.
UnDefend CVE-2026-45498 Microsoft Defender Antimalware Platform Denial of service / Defender disruption Fixed in platform versions at or above 4.18.26040.7; listed in CISA KEV.
RoguePlanet was originally disclosed as a race condition in mpengine.dll, the core scanning engine behind Windows Defender, that let a local attacker win a narrow check-then-act timing window during a file scan and redirect it into a command shell running as NT AUTHORITY\SYSTEM. Microsoft eventually acknowledged the bug... and remediated it in Malware Protection Engine version 1.1.26060.3008 during its July 2026 patch cycle.
16 indicators attributed to this actor: domains, IPs, hashes, and other artifacts pulled from reporting. View more in app.
20 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Published Windows zero-day/local privilege escalation exploits targeting Microsoft Windows and Windows Defender components, including ShieldBreak as a continuation of the previously reported RoguePlanet issue.
Released multiple zero-day exploits targeting Microsoft products, including the ShieldBreak proof-of-concept for privilege escalation on Windows via Microsoft Defender.
A named exploit-development cluster publicly releasing repeated unpatched Windows zero-days, primarily targeting Microsoft Defender and related Windows components, including patch bypasses for prior fixes.
A disclosure actor publishing Windows proof-of-concept techniques that abuse legitimate OS behavior for post-compromise privilege or profile-hijacking scenarios. In this content, it released the LegacyHive PoC, which modifies user registry hives offline, abuses NT Object Manager symbolic links and directories, uses oplocks for timing, and triggers profile loading via CreateProcessWithLogonW.
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Every observed MITRE ATT&CK technique, grouped by tactic.
Families this actor is known to deploy, with IOCs and behavior.
CVEs this actor has used in known campaigns.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Domains, IPs, and hashes tied to this actor, refreshed continuously.