A security researcher has publicly disclosed an exploit for a new Windows zero-day local privilege elevation vulnerability that gives admin privileges in Windows 10, Windows 11, and Windows Server. BleepingComputer reports: As part of the November 2021 Patch Tuesday, Microsoft fixed a ‘Windows Installer Elevation of Privilege Vulnerability’ vulnerability tracked as CVE-2021-41379. This vulnerability was discovered by security researcher Abdelhamid Naceri, who found a bypass to the patch and a more powerful new zero-day privilege elevation vulnerability after examining Microsoft’s fix. Yesterday, Naceri published a working proof-of-concept exploit for the new zero-day on GitHub, explaining that it works on all supported versions of Windows.
“This variant was discovered during the analysis of CVE-2021-41379 patch. the bug was not fixed correctly, however, instead of dropping the bypass,” explains Naceri in his writeup. “I have chosen to actually drop this variant as it is more powerful than the original one.” Furthermore, Naceri explained that while it is possible to configure group policies to prevent ‘Standard’ users from performing MSI installer operations, his zero-day bypasses this policy and will work anyway. BleepingComputer tested Naceri’s ‘InstallerFileTakeOver’ exploit, and it only took a few seconds to gain SYSTEM privileges from a test account with ‘Standard’ privileges, as demonstrated in [this video]. When BleepingComputer asked Naceri why he publicly disclosed the zero-day vulnerability, we were told he did it out of frustration over Microsoft’s decreasing payouts in their bug bounty program. A Microsoft spokesperson said in a statement: “We are aware of the disclosure and will do what is necessary to keep our customers safe and protected. An attacker using the methods described must already have access and the ability to run code on a target victim’s machine.”
Naceri recommends users wait for Microsoft to release a security patch, as attempting to patch the binary will likely break the installer.