Researchers uncovered a simple flaw that existed in nearly 28 Antivirus software that allows malware authors to exploit the system and disable the Antivirus software also turn them into self-destructive tools.
The bug abusing the directory junctions (Windows) and symlinks (macOS & Linux) operation and used it to perform this exploitation.
A directory junction is exclusive to Windows and can only link two directories together; It cannot link files and the directories must be local to the file system.
There is no admin privilege required to exploiting antivirus software that running under the Windows operating system.
A symlink Also called as symbolic link is commonly used within Linux and macOS. Symlink is a type of file that points to another file.
Using both methods, the flaw leverages the privileged file operations to disable the antivirus software or interfere with the operating system to render it useless, etc.
Basically, Antivirus will run in the computers with high privileged state and gaining the highest level of authority to scan all the files and directories to find the unknown and malicious files plus quarantined and moved to the isolated environment.
Due to this nature of the Antivirus, it opens to a wide range of vulnerabilities and various race conditions. eventually, it allows attackers to gain the high-level privilege of vulnerable systems.
Exploitation and Impact
The Exploitation work is simple and the experience malware authors can easily exploit the flaw. but it is highly time-sensitive and import to figure out when to performing the directory junction or symlink.
A local attacker who can attempt to escalate the privilege would be able to find out the correct timing to exploit the flaw.
According to the rack911labs report, “In some of the antivirus software that we exploited, the timing wasn’t important at all and a simple loop statement of running the exploit over and over was all that was needed to manipulate the antivirus software into self-destructing. One second too early or one second too late and the exploit will not work.”
Exploiting Windows (PoC Video)
Researchers attempted the exploitation process against McAfee Endpoint Security for Windows using their proof-of-concept, and they were able to delete the EpSecApiLib.dll file.
“In our testing, we were able to delete any file that was not currently in use including the ability to interfere with the antivirus operations itself”, researchers said.
rd /s /q C:UsersUserDesktopexploit
echo X5O!P%%@AP[4PZX54(P^^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H* > C:UsersUserDesktopexploitEpSecApiLib.dll
rd /s /q C:UsersUserDesktopexploit
mklink /J C:UsersUserDesktopexploit “C:Program Files (x86)McAfeeEndpoint SecurityEndpoint Security Platform”
Exploiting macOS & Linux (PoC Video)
Researchers used their PoC exploit against Norton Internet Security for macOS and downloads the EICAR test-string from Pastebin to bypass real-time protection that leads to preventing the Antivirus to download the test-string from the Norton official website.
While downloading the test-string from Pastebin, the Antivirus immediately detects it as malware and attempt to clean up.
Researchers said ” we were able to identify an approximate delay of 6-8 seconds that allows a race condition to occur that can result in a symlink attack causing any file to be removed due to the fact that the software runs as root.”
Poc Exploit code for MacOS
rm -rf /Users/Username/exploit ; mkdir /Users/Username/exploit
curl -k https://pastebin.com/raw/jZJ6Ekzt > /Users/Username/exploit/passwd
rm -rf /Users/Username/exploit ; ln -s /etc /Users/Username/exploit
This Proof-of-concept also works for some Linux antivirus software and the researchers were able to delete important files that would have rendered the antivirus software.
All the affected Anti-Virus vendors are individually confirmed and almost every antivirus vendor mentioned on this page is now patched.
Users are recommended to apply the newly released patch for the respect Antivirus software that you are installed on your computer.