BlueHammer
CVE-2026-33825, also referred to as BlueHammer, is a local elevation of privilege vulnerability in Microsoft Defender. Microsoft describes it as an insufficient granularity of access control issue, and multiple supporting reports characterize the underlying bug as a TOCTOU race condition in Defender’s threat remediation engine. Successful exploitation allows an authorized local attacker to abuse Defender’s privileged remediation behavior and escalate privileges to SYSTEM. The flaw was publicly disclosed before patching, proof-of-concept exploit code was released, and exploitation in the wild was subsequently reported. Microsoft patched the issue in its April 2026 Patch Tuesday updates.
Are you exposed to this one?
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Impact, mitigation & remediation
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
Impact
What an attacker gets, and what they’ve been doing with it.
Mitigation
If you can’t patch tonight, do this now.
Remediation
Patch, then assume compromise.
Exploits
1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos (5 hidden).
Small Windows-focused exploit repository for CVE-2026-33825 containing a single substantive source file, src/main.cpp, built with CMake. The code is a local privilege-escalation style PoC rather than a remote exploit. It uses low-level Windows and NT native APIs from ntdll.dll, plus Cloud Files API headers/libraries, to manipulate filesystem objects, enumerate object-manager directories, and set reparse points/mount points. The exploit workflow appears to prepare filesystem redirection primitives, race or coerce privileged file operations, then open \??\C:\Windows\System32\TieringEngineService.exe with FILE_SUPERSEDE semantics. After successful overwrite/placement, it copies its own executable into %WINDIR%\System32\TieringEngineService.exe and invokes LaunchTierManagementEng() to trigger execution. Repository structure is minimal: CMakeLists.txt for building, a short README naming CVE-2026-33825, and one large C++ implementation file. No network communication, C2, or external URLs are present; the exploit is entirely local and centered on Windows filesystem/object-manager abuse and privileged binary planting.
Affected products & vendors
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
Recent activity
121 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A specific Windows zero-day discussed as part of the Nightmare-Eclipse/Chaotic Eclipse set of six vulnerabilities tied to disputes over MSRC handling. The content states that three of those vulnerabilities were actively exploited before patches were available, but does not specify which three.
A Windows zero-day publicly disclosed with working proof-of-concept exploit code; it targeted core Windows components and was later weaponized in real-world attacks, leading to inclusion in CISA's KEV catalog.
A privilege-escalation vulnerability in Windows Defender that was publicly disclosed with PoC exploit code and is described as having been quickly exploited in the wild.
A local privilege escalation vulnerability referred to as BlueHammer affecting Windows Defender, notable here because an exploit is being added to Metasploit.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.