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Experts published unpatched Windows zero-day BlueHammer
April 07, 2026 
A researcher leaked the unpatched Windows zero-day “BlueHammer,” letting attackers gain SYSTEM rights; no patch exists yet.
A disgruntled researcher released the BlueHammer Windows zero-day, a privilege escalation flaw that allows attackers to gain SYSTEM or admin rights, Bleeping Computer reports.
The researcher privately reported the vulnerability to Microsoft but criticized the way the Microsoft’s Security Response Center (MSRC) managed the disclosure process. On April 3rd, the expert published the BlueHammer exploit on GitHub under the alias Nightmare-Eclipse. Microsoft hasn’t released a patch, so the flaw qualifies as a zero-day and leaves Windows systems open to potential attacks.
“I’m just really wondering what was the math behind their decision, like you knew this was going to happen and you still did whatever you did ? Are they serious ?” reads the description published in the Github repository hosting the BlueHammer vulnerability.
Nightmare-Eclipse pointed out that he inserted a few bugs in the PoC exploit code that could prevent it from working.
Popular cybersecurity experts Will Dormann confirmed that the BlueHammer exploit works. It’s a local privilege escalation (LPE) flaw combining TOCTOU and path confusion. The exploitation is not easy, however it can let a local attacker access the Security Account Manager (SAM) database with password hashes. With this access, attackers can escalate to SYSTEM privileges, potentially fully compromising the machine and spawning SYSTEM-level shells to control the system.
“There’s a new Windows 0day LPE that has been disclosed called BlueHammer [github.com]. The reporter suggests [deadeclipse666.blogspot.com] that it’s being disclosed due to how MSRC operates these days.” Dormann wrote on Mastodon. “MSRC used to be quite excellent to work with.
But to save money Microsoft fired the skilled people, leaving flowchart followers.
I wouldn’t be surprised if Microsoft closed the case after the reporter refused to submit a video of the exploit, since that’s apparently an MSRC requirement now.”
Even though BlueHammer needs local access, it poses a serious risk, attackers can reach the system via social engineering, stolen credentials, or by exploiting other vulnerabilities
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(SecurityAffairs – hacking, BlueHammer)
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