CVE-2017-8307 in Avast
Summary
by MITRE
In Avast Antivirus before v17, using the LPC interface API exposed by the AvastSVC.exe Windows service, it is possible to launch predefined binaries, or replace or delete arbitrary files. This vulnerability is exploitable by any unprivileged user when Avast Self-Defense is disabled. It is also exploitable in conjunction with CVE-2017-8308 when Avast Self-Defense is enabled. The vulnerability allows for Denial of Service attacks and hiding traces of a possible attack.
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Analysis
by VulDB Data Team • 12/21/2020
The vulnerability described in CVE-2017-8307 represents a critical privilege escalation flaw within Avast Antivirus software versions prior to v17. This vulnerability specifically targets the LPC (Local Procedure Call) interface API that is exposed by the AvastSVC.exe Windows service, which operates with elevated privileges. The flaw stems from insufficient access controls and improper input validation within the service's communication interface, allowing unauthorized users to manipulate system files through predefined binary execution paths or by performing file replacement and deletion operations. The vulnerability exists in the Windows service architecture where the AvastSVC.exe process maintains elevated privileges while exposing an interface that does not adequately verify the authenticity or authorization of incoming requests.
The technical exploitation of this vulnerability occurs through the LPC communication mechanism, which is a Windows inter-process communication method designed for local processes. Attackers can leverage this interface to send specially crafted requests that trigger the execution of predefined binaries or manipulate files within the system. The vulnerability is particularly dangerous because it operates at the kernel level through the Windows service interface, bypassing normal user permission checks. The flaw allows for arbitrary file operations including replacement and deletion, which can be used to compromise system integrity and maintain persistence. The vulnerability is classified under CWE-264, which addresses permissions, privileges, and access controls, specifically focusing on insufficient privileges or access control mechanisms.
The operational impact of CVE-2017-8307 extends beyond simple privilege escalation to enable comprehensive system compromise and attack persistence. An unprivileged user can exploit this vulnerability to execute arbitrary code with system-level privileges, effectively bypassing standard user access controls and security boundaries. This capability enables attackers to perform Denial of Service attacks by corrupting critical system files or removing essential components, rendering the system unstable or unusable. The vulnerability also facilitates stealthy attack operations by allowing threat actors to delete or replace files that might otherwise reveal evidence of compromise, making forensic analysis more difficult. The combination of this vulnerability with CVE-2017-8308 creates a powerful exploitation chain that can bypass the Avast Self-Defense feature, which is designed to protect against such attacks. According to ATT&CK framework, this vulnerability maps to T1055 (Process Injection) and T1068 (Exploitation for Privilege Escalation) techniques, while also enabling T1070 (Indicator Removal on Host) through file manipulation capabilities.
The exploitation conditions for this vulnerability are relatively straightforward, requiring only that Avast Self-Defense be disabled or that attackers combine this vulnerability with CVE-2017-8308 for exploitation when Self-Defense is enabled. This makes the vulnerability particularly dangerous in environments where Avast antivirus is installed without proper configuration or where users may inadvertently disable security features. The vulnerability demonstrates a classic security misconfiguration where a privileged service exposes an interface without proper authentication or authorization checks. System administrators should be aware that this vulnerability affects not just individual systems but potentially entire enterprise networks if Avast is deployed across multiple endpoints. The attack surface is widened by the fact that the vulnerability can be exploited by any local user, making it particularly dangerous in multi-user environments or shared computing systems.
Mitigation strategies for CVE-2017-8307 should focus on immediate software updates to Avast versions v17 or later, where the vulnerability has been patched. Organizations should also implement strict access controls and monitor for unauthorized changes to system files through integrity checking mechanisms. The Windows service configuration should be reviewed to ensure that only authorized processes can communicate with AvastSVC.exe, and that proper authentication mechanisms are in place. Security monitoring should include detection of unusual LPC interface activity and file modification patterns that might indicate exploitation attempts. Additionally, organizations should disable Avast Self-Defense only when absolutely necessary and ensure that proper security policies are in place to prevent unauthorized access to system resources. The vulnerability highlights the importance of proper privilege separation and secure service design principles, emphasizing that services running with elevated privileges must implement robust access control mechanisms to prevent unauthorized manipulation.