In April 2026, Microsoft’s own security software got hit. Not once — three times. Security researchers tracked three separate zero-day vulnerabilities being actively exploited in Microsoft Defender, the antivirus software most Windows businesses rely on as their first line of defense.
Two of those exploits were patched. Two were not.
As of late April 2026, the vulnerabilities dubbed RedSun and UnDefend remained unpatched while attackers were actively using them to escalate privileges inside compromised systems. Your Defender install might be running right now, and the thing that’s supposed to protect you has known holes in it that the good guys are still trying to fix.
This is the nightmare scenario security teams talk about: the guard dog has fleas.
What This Actually Means for Your Business
Zero-day exploits are dangerous precisely because no patch exists when they go live. By the time most businesses hear about them, the window to get ahead of them has already closed — unless someone is watching.
Here’s the uncomfortable truth: most small and medium businesses don’t have a security team monitoring threat feeds. They rely on their antivirus to handle it. But when the antivirus itself is the attack surface, that strategy falls apart.
This is exactly why managed security makes sense for businesses that can’t hire a dedicated SOC team. Threat monitoring, patch cadence, and behavioral detection aren’t nice-to-haves — they’re the floor.
What NSI Tech Does Differently
We don’t just install software and walk away. Our managed security approach includes:
- Continuous monitoring — watching for anomalies even when patches are delayed
- Patch management with accountability — we track exposure windows and act, not wait
- Layered defense — because relying on any single product, including Microsoft’s, is a gamble
If you’re running Windows and think “we have Defender, we’re fine” — April 2026 is a good reminder that the threat landscape doesn’t wait for your next software update.
Ready to lock down your security posture? Talk to our team — no sales pressure, just a real conversation about where you stand.