Windows ALPC Heap-Based Buffer Overflow Privilege Escalation Vulnerability (CVE-2026-85880) Security Advisory

1. Apply Official Security Patches

Deploy the latest Cumulative Update (LCU) provided by Microsoft immediately.

• Via PowerShell (PSWindowsUpdate):

  Install-Module PSWindowsUpdate
  Get-WindowsUpdate -AcceptAll -Install -AutoReboot

2. Temporary Mitigations & Monitoring

If immediate patching is not feasible, implement the following controls:

• Enforce Least Privilege: Restrict local interactive logon rights and disable unnecessary Remote Desktop (RDP) access.
• EDR/SIEM Detection Rules: Monitor for anomalous process creation where a low-privilege parent process spawns a SYSTEM-level shell.

  // Example Splunk/SIEM Query for detecting anomalous privilege escalation
  index=windows EventCode=1 
  | search ParentImage="*\\explorer.exe" AND User="NT AUTHORITY\\SYSTEM" AND (Image="*\\cmd.exe" OR Image="*\\powershell.exe")

This vulnerability (CVE-2026-85880) is a heap-based buffer overflow (CWE-122) combined with an uninitialized memory reference (CWE-908) within the Windows Advanced Local Procedure Call (ALPC) port message handling mechanism.

Root Cause & Exploit Mechanics

• ALPC Message Processing Flaw: An attacker sends a specially crafted ALPC message to a local port. Due to insufficient boundary validation during message size calculation in the kernel, data is written beyond the allocated heap buffer in the Kernel Pool.
• Uninitialized Memory Disclosure: Under certain conditions, uninitialized memory buffers (CWE-908) are referenced, which can assist attackers in bypassing Kernel Address Space Layout Randomization (KASLR).
• Privilege Escalation: By leveraging this overflow, the attacker overwrites critical kernel structures (such as process tokens or function pointers) to elevate privileges from a standard user to NT AUTHORITY\SYSTEM.

Threat Intelligence Assessment

This vulnerability is listed in the CISA KEV (Known Exploited Vulnerabilities) catalog, confirming active in-the-wild exploitation. With an EPSS score of 0.94, weaponized exploits are highly likely to be integrated into post-exploitation frameworks, making immediate remediation critical to prevent lateral movement and full domain compromise.