GoKawiilWant to learn ethical hacking? I built a complete course. Have a look! Learn penetration testing, web exploitation, network security, and the hacker mindset: → Master ethical hacking hands-on (The link supports me directly as your instructor!) Hacking is not a hobby but a way of life!
Windows Defender, the built-in antivirus running on every Windows machine, has a zero-day exploit with full source code sitting on GitHub. No patch, no CVE, and confirmed working on fully updated Windows 10 and 11. A researcher who says Microsoft went back on their word just handed every attacker paying attention a privilege escalation that takes any low-privileged account straight to NT AUTHORITY\SYSTEM. On Windows Server the result is different but still serious: a standard user ends up with elevated administrator access. 😏
The vulnerability is called BlueHammer. On April 2nd the researcher posted the public disclosure on a personal blog, and on April 3rd the full exploit source code went live on GitHub. Both published under the alias Chaotic Eclipse, also known as Nightmare Eclipse, with a message to Microsoft’s Security Response Center that comes down to: I told you this would happen.
Before getting into the technical side, there is a backstory here worth knowing.
In late March, the same researcher opened a blog with a single post explaining that they never wanted to come back to public research. Someone had made an agreement with them and then broke it, knowing exactly what the consequences would be. The post says it left the researcher without a home and with nothing. A week later, BlueHammer went live on GitHub with a message that specifically thanks MSRC leadership for making it necessary. That is not someone annoyed with a slow review process. That is someone with nothing left to lose.
Now to the exploit itself, because this one is genuinely worth understanding.
BlueHammer is not a traditional bug, and it does not need shellcode, memory corruption, or a kernel exploit to work. What it does is chain five completely legitimate Windows components together in a sequence that produces something their designers never intended. Those five components are Windows Defender, Volume Shadow Copy Service, the Cloud Files API, opportunistic locks, and Defender’s internal RPC interface. One practical limitation worth knowing: the exploit needs a pending Defender signature update to be available at the time of the attack. Without one in the queue, the chain does not trigger. That makes it less reliable than a push-button exploit, but it does not make it safe to ignore.
Here is how the attack chain works.
When Defender runs an antivirus definition update, part of that process involves creating a temporary Volume Shadow Copy, which is the same snapshot mechanism Windows uses for backup and restore. That shadow copy contains files that are normally completely locked during regular operation, including the SAM database, which stores the password hashes for every local account on the machine.
BlueHammer registers itself as a Cloud Files sync provider, the same kind of thing that OneDrive or Dropbox uses to sync files. When Defender touches a specific file inside that folder, the exploit gets a callback and immediately places an opportunistic lock on that file. Defender stalls, blocked, waiting for a response that is never coming. The shadow copy it just created is still mounted. The window is open.
... continue reading