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04-28-2026, 06:45 PM
BlueHammer
BlueHammer (CVE-2026-33825) is what we call a Local Privilege Escalation (LPE) flaw. Put simply, it’s a way for a "nobody" account on a computer to suddenly gain admin or SYSTEM privileges.
The technical culprit here is a 'race condition'. Every few hours, Defender updates its virus definitions. BlueHammer exploits a tiny, millisecond-wide window during that update process. By tricking Defender into looking at the SAM (Security Account Manager) hive instead of an update file, the attacker can dump the encrypted passwords for every user on the machine.
It’s the digital equivalent of a thief waiting for a security guard to blink, then swapping the guard’s clipboard for a master key. By the time Defender finishes its "check," the keys are already gone.
RedSun
While Microsoft scrambled to patch BlueHammer, RedSun is the "zero-day" currently keeping sysadmins awake at night. This one is particularly cheeky because it uses Defender’s own helpfulness against it.
RedSun targets a logic flaw in how Defender handles files with "cloud tags" (those little markers used by services like OneDrive). Usually, if Defender finds a virus, it nukes it. But if a malicious file is tagged in a specific way, RedSun triggers a bug that makes Defender try to "restore" or "re-sync" the file to its original location.
The attacker uses a directory junction (a type of digital shortcut) to point that "original location" toward somewhere that's usually protected like `C:\Windows\System32`. Essentially, Defender, running with the highest possible permissions, ends up hand-delivering the attacker’s malware directly into the most sensitive part of the OS. It’s not a break-in; it’s the guard holding the door open for the intruder.
UnDefend
If the first two are about breaking in, UnDefend is about making sure no one notices. It’s a defense-evasion tool that messes with Defender’s update pipeline. It generally operates in two modes:
Since RedSun and UnDefend are still in the wild without a fix, you can’t just click "Update" and call it a day. You need to be a bit more proactive:
BlueHammer (CVE-2026-33825) is what we call a Local Privilege Escalation (LPE) flaw. Put simply, it’s a way for a "nobody" account on a computer to suddenly gain admin or SYSTEM privileges.
The technical culprit here is a 'race condition'. Every few hours, Defender updates its virus definitions. BlueHammer exploits a tiny, millisecond-wide window during that update process. By tricking Defender into looking at the SAM (Security Account Manager) hive instead of an update file, the attacker can dump the encrypted passwords for every user on the machine.
It’s the digital equivalent of a thief waiting for a security guard to blink, then swapping the guard’s clipboard for a master key. By the time Defender finishes its "check," the keys are already gone.
RedSun
While Microsoft scrambled to patch BlueHammer, RedSun is the "zero-day" currently keeping sysadmins awake at night. This one is particularly cheeky because it uses Defender’s own helpfulness against it.
RedSun targets a logic flaw in how Defender handles files with "cloud tags" (those little markers used by services like OneDrive). Usually, if Defender finds a virus, it nukes it. But if a malicious file is tagged in a specific way, RedSun triggers a bug that makes Defender try to "restore" or "re-sync" the file to its original location.
The attacker uses a directory junction (a type of digital shortcut) to point that "original location" toward somewhere that's usually protected like `C:\Windows\System32`. Essentially, Defender, running with the highest possible permissions, ends up hand-delivering the attacker’s malware directly into the most sensitive part of the OS. It’s not a break-in; it’s the guard holding the door open for the intruder.
UnDefend
If the first two are about breaking in, UnDefend is about making sure no one notices. It’s a defense-evasion tool that messes with Defender’s update pipeline. It generally operates in two modes:
- It quietly blocks all new virus signature updates. The software stays "on," but it's essentially looking for yesterday’s threats while ignoring today’s.
- This is the dangerous part. UnDefend is designed to "gaslight" management consoles. Your IT dashboard will show a big green checkmark saying the machine is "Healthy and Up to Date," while in reality, the engine hasn't seen a fresh signature in days.
Since RedSun and UnDefend are still in the wild without a fix, you can’t just click "Update" and call it a day. You need to be a bit more proactive:
- Look for any non-admin users creating NTFS junctions or mount points. That’s a major RedSun red flag.
- If a machine's signature version hasn't changed in 48 hours, go check it manually. Don’t let the "Green Checkmark" of UnDefend lie to you.
- Use Attack Surface Reduction (ASR) rules. Specifically, block Office apps from creating child processes and stop scripts from running out of the Downloads folder.
