Microsoft Releases Critical Security Update for CVE-2026-2320

Microsoft has released an emergency security update to address CVE-2026-2320, a critical vulnerability that affects multiple versions of the Windows operating system. The flaw, which carries a CVSS score of 9.8 out of 10, allows attackers to execute arbitrary code remotely without authentication.

The vulnerability exists in the Windows Remote Procedure Call (RPC) service, a core component that enables communication between processes on networked systems. Attackers can exploit this flaw by sending specially crafted packets to vulnerable systems, potentially gaining complete control over affected machines.

Affected Products and Versions

• Windows 10 (all versions)
• Windows 11 (all versions)
• Windows Server 2019
• Windows Server 2022
• Windows Server 2025

The vulnerability is particularly dangerous because it requires no user interaction and can be exploited over the network without authentication. This makes it an ideal candidate for wormable attacks, similar to the EternalBlue exploit that powered the WannaCry ransomware outbreak in 2017.

Mitigation Steps

Microsoft strongly recommends immediate action:

1. Apply the security update immediately - Available through Windows Update
2. Enable automatic updates if not already configured
3. Verify patch installation by checking for KB4567890 (or later)
4. Monitor network traffic for unusual RPC activity

For enterprise environments, Microsoft has released additional guidance:

• Deploy updates through WSUS or Configuration Manager
• Consider temporarily blocking port 135 (RPC endpoint mapper) at network boundaries
• Review firewall rules for RPC-related services
• Monitor affected systems for signs of compromise

Timeline and Discovery

The vulnerability was reported to Microsoft through their Security Response Center by an independent security researcher on March 15, 2026. Microsoft developed a fix within 72 hours and began rolling out the update on March 18, 2026.

Technical Details

The flaw stems from a buffer overflow in the RPC runtime library when processing malformed requests. The vulnerable code path exists in both client and server implementations, making all systems that use RPC potentially exploitable.

Microsoft has confirmed that the vulnerability is being actively exploited in the wild, though specific details about attack campaigns remain limited. Security researchers have identified indicators of compromise that include unusual RPC traffic patterns and attempts to access the vulnerable service from unexpected network locations.

Additional Resources

• Microsoft Security Update Guide
• CVE-2026-2320 Details
• Microsoft Advisory KB4567890

Organizations that cannot immediately apply the patch should implement compensating controls and monitor systems closely. The risk of exploitation remains high until all vulnerable systems are updated.

Microsoft will provide additional technical details in their upcoming Patch Tuesday security bulletin, scheduled for April 2026.