CVE-2015-8620 in Avast!
Summary
by MITRE
Heap-based buffer overflow in the Avast virtualization driver (aswSnx.sys) in Avast Internet Security, Pro Antivirus, Premier, and Free Antivirus before 11.1.2253 allows local users to gain privileges via a Unicode file path in an IOCTL request.
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Analysis
by VulDB Data Team • 07/08/2022
The vulnerability CVE-2015-8620 represents a critical heap-based buffer overflow within the Avast virtualization driver component known as aswSnx.sys. This flaw exists in multiple Avast antivirus products including Internet Security, Pro Antivirus, Premier, and Free Antivirus versions prior to 11.1.2253. The vulnerability stems from inadequate input validation within the driver's handling of IOCTL (Input/Output Control) requests, specifically when processing Unicode file paths. The buffer overflow occurs in the kernel-mode driver context, making it particularly dangerous as it can be exploited by local attackers to escalate privileges from standard user level to SYSTEM level access.
The technical implementation of this vulnerability involves the driver's failure to properly validate the length of Unicode strings when processing IOCTL requests. When a malicious local user submits an IOCTL request containing an excessively long Unicode file path, the driver attempts to copy this data into a heap-allocated buffer without sufficient bounds checking. This heap-based buffer overflow creates memory corruption that can be leveraged to execute arbitrary code within the kernel context. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, though the specific implementation results in heap corruption due to the driver's memory management patterns.
The operational impact of this vulnerability is severe and multifaceted. Local attackers with minimal privileges can exploit this flaw to achieve privilege escalation, potentially gaining SYSTEM-level access to compromised systems. This escalates the attack surface significantly as the attacker can then access protected system resources, modify critical system files, disable security features, and establish persistent backdoors. The vulnerability affects multiple Avast product lines, amplifying its potential impact across various user bases. The exploitability is relatively straightforward since it requires only local access to the system and knowledge of the specific IOCTL interface.
Mitigation strategies for this vulnerability should focus on immediate patching of affected Avast products to version 11.1.2253 or later, which contains the necessary driver updates addressing the buffer overflow. System administrators should also implement additional security measures including privilege separation, monitoring for unusual IOCTL activity, and regular security assessments of kernel-mode drivers. The vulnerability demonstrates the importance of proper input validation in kernel drivers and aligns with ATT&CK technique T1068 which covers privilege escalation through kernel exploits. Organizations should also consider implementing the principle of least privilege and maintaining up-to-date antivirus solutions to prevent exploitation of similar driver-based vulnerabilities. The incident highlights the critical need for comprehensive security testing of kernel-mode components and proper memory management practices in security software implementations.