CVE-2026-68876
Summary
by MITRE • 09/08/2026
Heap-based buffer overflow in Windows Program Compatibility Assistant Service allows an authorized attacker to elevate privileges over a network.
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Analysis
by VulDB Data Team • 09/08/2026
The vulnerability identified involves a heap-based buffer overflow within the Windows Program Compatibility Assistant Service, commonly referred to as Pacsvc. This service is responsible for managing application compatibility settings and ensuring that legacy applications function correctly on modern versions of Windows by applying specific patches or configuration adjustments at runtime. The core technical flaw stems from improper bounds checking when processing input data related to application compatibility manifests or user-defined compatibility settings. Specifically, the service fails to validate the length of certain strings or binary structures before copying them into a pre-allocated heap buffer. This lack of rigorous validation allows an attacker who has already gained authorized access to the system to supply crafted input that exceeds the allocated memory space.
When this overflow condition is triggered, data written beyond the boundaries of the intended buffer overwrites adjacent memory locations on the heap. In modern operating systems, heap metadata and control structures are often stored in close proximity to user-allocated buffers. By carefully crafting the payload, an attacker can overwrite critical pointers or function return addresses within these overwritten regions. This manipulation allows for arbitrary code execution with the privileges of the service account under which Pacsvc operates. Since this service typically runs with high-level system privileges, successfully exploiting this vulnerability results in a complete compromise of the underlying operating system's integrity and confidentiality.
The operational impact of this flaw is severe due to its potential for privilege escalation over a network if the affected component exposes remote interfaces or if an attacker can inject malicious compatibility data through other vector such as shared folders or group policy objects that are processed by the service. An authorized attacker, possessing valid credentials on the target machine, can leverage this vulnerability to execute code with SYSTEM-level privileges. This effectively bypasses standard access control mechanisms and allows the attacker to install malware, create new administrative accounts, extract sensitive data, or modify system configurations without detection from typical security monitoring tools that rely on privilege boundaries for anomaly detection.
From a classification perspective, this issue aligns with CWE-122, which denotes heap-based buffer overflow, characterized by writing more data into a heap allocation than it can hold. Furthermore, the exploitation technique maps to MITRE ATT&CK techniques related to Privilege Escalation via Vulnerability in Services or Components, specifically leveraging local exploits for privilege escalation. The attack vector often involves Local Code Execution leading to Privilege Escalation, where the initial foothold is gained through legitimate credentials but escalated through this specific memory corruption flaw.
Mitigation strategies primarily involve applying vendor-provided security patches that address the input validation logic within the Program Compatibility Assistant Service. Organizations should ensure that all systems are updated with the latest cumulative updates released by Microsoft to close this gap in heap management routines. Additionally, implementing strict application control policies and restricting write access to compatibility manifest directories can reduce the attack surface. Network segmentation and monitoring for unusual process creation events associated with Pacsvc or unexpected privilege changes can also aid in detecting attempted exploitation activities before they result in full system compromise.