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Nightmare-Eclipse is an anonymous exploit developer and public disclosure actor active in 2026, also tracked under the aliases Chaotic Eclipse, Dead Eclipse, and MSNightmare. The actor is known for repeatedly publishing uncoordinated proof-of-concept exploits and abuse techniques targeting Microsoft Windows security components, especially Microsoft Defender, the Windows User Profile Service, Windows Recovery Environment, BitLocker-related workflows, and adjacent operating-system trust boundaries. The activity is best characterized as a disclosure-driven exploit cluster centered on Windows local privilege escalation, security-feature bypass, and post-compromise abuse rather than a conventional intrusion set. Publicly attributed releases in this cluster include BlueHammer, RedSun, UnDefend, YellowKey, GreenPlasma, MiniPlasma, RoguePlanet, GreatXML, and LegacyHive. Multiple releases abused legitimate Windows features and workflow interactions rather than memory corruption, including combinations of Volume Shadow Copy behavior, opportunistic locks, Cloud Files placeholders, NTFS junctions and reparse points, Object Manager symbolic links, offline registry hive modification, scheduled task execution, and WinRE answer-file processing. Several tools demonstrated elevation from a standard user to SYSTEM, while others focused on Defender evasion or disruption, BitLocker and login bypass, or cross-user registry hive loading. LegacyHive in particular demonstrated cross-user hive redirection through profile-loading abuse, and GreatXML demonstrated a persistence and data-access primitive against BitLocker-protected systems after prior administrative compromise. The actor’s disclosures have been associated with multiple Windows zero-days or n-day exploit releases, including vulnerabilities later tracked as CVE-2026-33825, CVE-2026-41091, and CVE-2026-45498. Reporting also states that some earlier Nightmare-Eclipse releases were observed in real-world attack chains after publication. The actor has used public code-hosting platforms and mirrors to distribute exploit material, and repositories were removed by major platforms before copies spread elsewhere. The real identity of the operator remains unknown. Available evidence supports a profile of a disgruntled or adversarial security researcher focused on pressuring Microsoft through public release of exploit code rather than a clearly attributed state-backed espionage actor or ransomware operator.
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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.
45 distinct techniques observed across reporting, grouped by tactic. Hover any cell for the evidence excerpt; click through for MITRE's full description.
9 malware families attributed to this actor across reporting.
4 additional families tracked in Mallory.
3 CVEs this actor has used in observed campaigns. 3 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.
10 indicators attributed to this actor: domains, IPs, hashes, and other artifacts pulled from reporting. View more in app.
17 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
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.
An earlier 2026 uncoordinated disclosure campaign described as Windows-focused and grievance-driven, referenced here for comparison with Exploitarium.
Publicly releasing unpatched zero-day exploits targeting Microsoft products, including a Windows local privilege escalation exploit dubbed LegacyHive.
A named researcher/activity cluster associated with releasing a toolkit of Windows-focused offensive security tools and primitives, including the LegacyHive registry hive loading primitive affecting the Windows User Profile Service.
Match sector + geo + tech-stack targeting against your real footprint.
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.