CVE-2020-20118 in AntiVirus
Summary
by MITRE • 07/11/2023
Buffer Overflow vulnerability in Avast AntiVirus before v.19.7 allows a local attacker to cause a denial of service via a crafted request to the aswSnx.sys driver.
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Analysis
by VulDB Data Team • 07/28/2023
The vulnerability CVE-2020-20118 represents a critical buffer overflow flaw within Avast AntiVirus software versions prior to 19.7, specifically affecting the aswSnx.sys kernel driver component. This issue arises from insufficient input validation mechanisms within the driver's handling of user-supplied data, creating an exploitable condition that can be leveraged by local attackers to execute arbitrary code or cause system instability. The vulnerability exists at the kernel level, making it particularly dangerous as it operates with elevated privileges and can bypass standard user-mode security controls. The affected driver is responsible for network traffic monitoring and filtering functions within the antivirus ecosystem, making it a prime target for exploitation. According to CWE-121, this vulnerability falls under the category of stack-based buffer overflow, where the malicious input exceeds the allocated buffer space and overwrites adjacent memory regions, potentially leading to arbitrary code execution or system crashes. The flaw demonstrates characteristics consistent with ATT&CK technique T1059.003, where adversaries may exploit system-level vulnerabilities to gain persistent access or escalate privileges within the target environment.
The technical implementation of this buffer overflow occurs when the aswSnx.sys driver receives crafted input through improper validation of data structures passed from user mode to kernel mode. Attackers can construct malicious requests that contain oversized data payloads, causing the driver to write beyond the intended buffer boundaries. This overflow can corrupt critical kernel memory structures including function pointers, return addresses, or other control data that governs the driver's execution flow. The vulnerability is particularly concerning because it requires no special privileges to exploit, as the driver itself operates with elevated permissions necessary for system-level operations. The buffer overflow can be triggered through various attack vectors including malformed network packets, corrupted configuration files, or specially crafted API calls that are processed by the vulnerable driver component. Memory corruption resulting from such exploitation can manifest as system crashes, blue screen errors, or more insidiously, allow for privilege escalation attacks that can ultimately compromise the entire system.
The operational impact of CVE-2020-20118 extends beyond simple denial of service scenarios, as local attackers with minimal privileges can leverage this vulnerability to gain unauthorized access to system resources and potentially execute arbitrary code with kernel-level privileges. The attack surface is broadened by the fact that the vulnerable driver is actively monitoring network traffic, meaning that attackers could potentially exploit this through network-based attacks or by compromising systems through other attack vectors that lead to local execution. System administrators face significant challenges in mitigating this vulnerability since it affects core antivirus functionality and requires careful patch management to resolve. Organizations that have not updated to Avast version 19.7 or later remain at risk of exploitation, particularly in environments where privilege separation is not properly enforced. The vulnerability also impacts compliance with security standards such as those outlined in NIST SP 800-53, where inadequate input validation and memory management practices can lead to system integrity breaches that violate security control requirements.
Mitigation strategies for CVE-2020-20118 focus primarily on immediate patch deployment to update Avast AntiVirus to version 19.7 or later, which includes proper bounds checking and input validation mechanisms within the aswSnx.sys driver. System administrators should implement comprehensive patch management policies that prioritize critical security updates, particularly those affecting kernel-mode drivers that can compromise system integrity. Additional protective measures include disabling unnecessary network monitoring features, implementing strict access controls for antivirus driver components, and conducting regular security assessments to identify similar vulnerabilities in other system components. The vulnerability highlights the importance of kernel-mode security testing and the need for robust input validation practices as recommended by OWASP Top 10 security principles. Organizations should also consider implementing monitoring solutions that can detect anomalous behavior in system drivers, as this vulnerability could potentially be exploited in advanced persistent threat scenarios. Regular security awareness training for system administrators should emphasize the critical nature of timely patch deployment and the potential consequences of running outdated security software versions.