CVE-2019-17093 in Avast
Summary
by MITRE
An issue was discovered in Avast antivirus before 19.8 and AVG antivirus before 19.8. A DLL Preloading vulnerability allows an attacker to implant %WINDIR%\system32\wbemcomn.dll, which is loaded into a protected-light process (PPL) and might bypass some of the self-defense mechanisms. This affects all components that use WMI, e.g., AVGSvc.exe 19.6.4546.0 and TuneupSmartScan.dll 19.1.884.0.
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Analysis
by VulDB Data Team • 01/27/2024
This vulnerability represents a critical DLL preloading flaw in Avast and AVG antivirus products that existed prior to versions 19.8. The security issue stems from improper handling of dynamic link library loading sequences within the Windows Management Instrumentation framework, specifically affecting the wbemcomn.dll component located in the system32 directory. The vulnerability allows attackers to execute malicious code with elevated privileges by leveraging the Windows process protection mechanisms that were designed to prevent such attacks. This particular flaw is especially concerning because it targets protected-light processes that are specifically engineered to resist tampering and self-defense mechanism bypass attempts.
The technical implementation of this vulnerability exploits the Windows DLL search order mechanism where applications load libraries from the current working directory before checking system directories. When Avast and AVG products utilize WMI components for various functions including AVGSvc.exe and TuneupSmartScan.dll, they inadvertently create opportunities for attackers to place malicious DLLs in strategic locations. The wbemcomn.dll file serves as a key target because it is loaded into protected-light processes that should normally prevent unauthorized modifications. This creates a dangerous scenario where legitimate system components can be replaced with malicious equivalents that execute within the context of highly privileged processes, effectively circumventing the intended security protections.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass comprehensive system compromise capabilities. Attackers can leverage this flaw to execute arbitrary code with system-level privileges while bypassing traditional antivirus self-defense mechanisms that are typically effective against such attacks. The affected components including AVGSvc.exe and TuneupSmartScan.dll represent core antivirus functionality that would normally be protected from tampering, yet the vulnerability allows attackers to inject malicious code that operates within the same protected context. This creates a persistent threat vector that can maintain system access and potentially escalate further through additional exploitation techniques.
Security mitigation strategies should focus on immediate patching of affected antivirus versions to 19.8 or later, where the DLL loading behavior has been corrected to properly prioritize system directories over current working directories. System administrators should also implement monitoring for suspicious DLL loading patterns and establish strict file integrity controls around system32 directories. The vulnerability aligns with CWE-426 Untrusted Search Path and ATT&CK technique T1055 Process Injection, representing a sophisticated attack vector that combines multiple exploitation methods to achieve system compromise. Organizations should conduct thorough security assessments of their antivirus installations and consider implementing additional process monitoring to detect anomalous behavior in protected processes that might indicate exploitation attempts.