Avast Premium Security Driver Vulnerability Enables Local Privilege Escalation

Executive Summary

A high-severity local privilege escalation (LPE) vulnerability in the self-protection driver of Avast Premium Security could allow an authenticated attacker to gain SYSTEM-level privileges on a compromised Windows host. Tracked as CVE-2026-5424 and assigned a CVSS v3.1 base score of 7.8 by Trend Micro's Zero Day Initiative (ZDI), the flaw stems from an exposed, dangerous function within the kernel-mode driver. Successful exploitation requires an attacker to first obtain the ability to execute low-privileged code on the target system.

Technical Analysis

The vulnerability resides in the genkprot.sys driver, a core component of Avast Premium Security's self-protection mechanism designed to shield the antivirus processes and registry keys from tampering. According to ZDI's advisory (ZDI-26-271), the driver improperly exposes a function via its I/O Control (IOCTL) interface that provides direct write-what-where capabilities. This function lacks proper validation, allowing a user with low privileges to call it and write arbitrary data to arbitrary kernel memory addresses.

This type of vulnerability is a classic example of a poorly secured driver interface. By granting a user-mode process the ability to perform controlled writes to the kernel, an attacker can corrupt critical data structures to elevate their privileges. The attack path would typically involve overwriting a token value in memory to that of the SYSTEM user or a similar high-integrity account. The ZDI advisory notes the specific flaw is an "Exposed Dangerous Function" vulnerability, a category where a driver provides a function that is inherently unsafe if accessible from user space without stringent safeguards.

Tactics, Techniques & Procedures

If exploited, this vulnerability would align with the following MITRE ATT&CK techniques:

• TA0004: Privilege Escalation – The primary goal of the exploit.
• T1068: Exploitation for Privilege Escalation – Exploiting the driver flaw to gain higher privileges.
• T1547.006: Boot or Logon Autostart Execution: Kernel Modules and Extensions – The vulnerability exists in a kernel driver, which loads at boot.
• T1574.012: Hijack Execution Flow: COR_PROFILER – While not a direct match, the technique of hijacking trusted software components (like a security driver) is conceptually similar. An attacker would first need to establish a foothold on the target machine through other means (e.g., phishing, exploiting a separate application vulnerability) to run code as a standard user before leveraging this flaw for full system control.

Threat Actor Context

There is no public evidence linking CVE-2026-5424 to any specific threat actor or active exploitation campaign as of this writing. However, local privilege escalation vulnerabilities in security software are highly prized by advanced persistent threat (APT) groups and ransomware operators. Such flaws are often integrated into post-exploitation toolkits to solidify control over a compromised host, disable security software, and perform lateral movement. The driver is digitally signed by Avast Software s.r.o., which would lend the malicious code a veneer of legitimacy.

Mitigations & Recommendations

The primary mitigation is to apply the vendor-provided patch. Users of Avast Premium Security should ensure their software is updated to the latest version, which contains the fix. Avast typically deploys such updates automatically via its streaming update mechanism. Organizations should:

1. Verify that all endpoints running Avast Premium Security have received the latest updates.
2. Implement the principle of least privilege to limit the number of users with local administrative rights, thereby reducing the potential impact of a successful local privilege escalation.
3. Monitor for unexpected kernel-mode driver loads or unusual activity originating from Avast processes, though this can be challenging due to the legitimate nature of the driver. As a general security practice, organizations should consider deploying exploit protection measures, such as Microsoft's Attack Surface Reduction (ASR) rules and Windows Defender Exploit Guard, which can help mitigate some types of kernel exploitation.