A DLL hijacking vulnerability affecting Bitdefender Antivirus Free 2020 could have been exploited for privilege escalation and other malicious purposes, SafeBreach researchers revealed on Wednesday.
The vulnerability, tracked as CVE-2019-15295 with a CVSS score of 5.9 (medium severity), impacted Bitdefender Antivirus Free 2020 versions prior to 1.0.15.138, which patches the vulnerability. Bitdefender, which described the flaw as an untrusted search path issue, said the mitigation was delivered to affected users automatically.
According to SafeBreach, the security hole is related to the ServiceInstance.dll library, which is loaded by the BitDefender Update Service (updatesrv.exe) and the BitDefender Security Service (vsserv.exe), both of which are signed by Bitdefender and run with SYSTEM privileges. ServiceInstance.dll in turn loads a library called RestartWatchDog.dll.
The problem, SafeBreach said, was that RestartWatchDog.dll was not loaded safely and the antivirus application did not ensure that the loaded library file was signed. This allowed an attacker with access to a system running Bitdefender Antivirus Free 2020 to plant a malicious version of the library that would be executed instead of the legitimate version.
However, it’s important to note that for the attack to work a user or process with administrative privileges would first need to modify the system PATH variable to include the folder where the attacker wants to plant the malicious DLL, and to set the permissions for that directory so that non-admin users can write files to it.
Ensuring that a malicious library is loaded instead of the legitimate component can help attackers achieve various goals. For example, once the PATH modifications are made by an admin, a regular user can plant the malicious DLL, escalating its privileges to SYSTEM.
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