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CVE-2026-85880 is a heap-based buffer overflow vulnerability within the Windows Advanced Local Procedure Call (ALPC) subsystem. The ALPC mechanism is a fundamental component of the Windows operating system, responsible for high-speed, secure inter-process communication (IPC) between processes running at different integrity levels. This deep integration with core OS functionality makes it an attractive and potent target for attackers seeking to elevate privileges.
The technical root of this vulnerability lies in a boundary error during memory allocation and data copying operations. Specifically, the ALPC subsystem fails to perform sufficient validation of input data lengths before copying them into fixed-size buffers allocated on the heap. An authorized, low-privileged local attacker can exploit this flaw by invoking specific system calls or interacting with local services to supply an oversized payload. This triggers a heap-based buffer overflow, allowing the attacker to write data beyond the allocated buffer’s boundaries and corrupt adjacent memory structures.
By carefully crafting the overflow, an attacker can overwrite critical in-memory data, such as function pointers or object headers. This memory corruption can be leveraged to redirect program flow and execute arbitrary code. Due to the nature of the ALPC service, which often handles requests for highly privileged system processes, the injected code executes with SYSTEM-level privileges. This effectively grants the attacker full, unrestricted control over the compromised host without requiring any user interaction. Microsoft has confirmed that this vulnerability is being actively exploited in the wild as a zero-day.
DailyCVE Form:
Platform: ……. Microsoft Windows
Version: …….. 10, 11, Server
Vulnerability :…… Heap Buffer Overflow
Severity: ……. HIGH (CVSS 7.8)
date: ………. September 8, 2026
Prediction: … September 22, 2026
What Undercode Say:
The vulnerability allows a local user to escalate privileges on the system. The flaw exists due to a boundary error in Windows ALPC. A local user can trigger a heap-based buffer overflow and execute arbitrary code with SYSTEM privileges. It is being actively exploited.
Affected versions include:
Windows 10 21H2 (10.0.19044.7725)
Windows 10 22H2 (10.0.19045.7725)
Windows 10 1607 (10.0.14393.9512)
Windows 10 1809 (10.0.17763.9245)
Windows Server 2012 R2 (6.3.9600.23397)
Windows Server 2012 (6.2.9200.26349)
Windows Server 2016 (10.0.14393.9512)
Windows Server 2019 (10.0.17763.9245)
Windows Server 2022 (10.0.20348.5622)
Exploit: (Educational Purposes!)
To understand the exploitation vector, consider the following simplified conceptual demonstration. This is for educational purposes only and does not represent a functioning exploit.
Conceptual steps an attacker might take: 1. Identify a vulnerable ALPC service endpoint. 2. Craft a malicious ALPC message with an oversized payload. 3. Send the message to the vulnerable service. 4. Trigger the heap overflow to overwrite a function pointer. 5. Redirect execution to attacker-controlled shellcode.
A real-world exploit would involve complex heap spraying techniques to reliably position shellcode and achieve arbitrary code execution.
Protection:
The primary and most effective mitigation is to apply the official security updates provided by Microsoft. Ensure all affected Windows endpoints and servers are patched immediately.
Additional defensive measures include:
- Enabling Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR) to make exploitation more difficult.
- Monitoring system logs for unusual ALPC activity or unexpected privilege changes.
- Implementing application whitelisting and strict access controls to limit interaction with sensitive system components.
Impact:
Successful exploitation of CVE-2026-85880 allows a local attacker to elevate privileges from a standard user account to SYSTEM. This grants the attacker full control over the operating system, enabling them to:
– Install persistent backdoors.
– Modify or disable security policies and defensive mechanisms like antivirus software.
– Exfiltrate sensitive data.
– Use this access as a stepping stone for further network compromise.
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Sources:
Reported By: www.cve.org
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