Cybersecurity researchers have shared a proof-of-concept (PoC) exploit for what they claim is an unpatched zero-day privilege elevation vulnerability that affects all versions of WIndows, including the just released Windows 11.
Successfully exploiting the bug enables the attackers to gain SYSTEM privileges on the targeted Windows computer.
However, the only saving grace is that the exploit requires the threat actor to know the login credentials of a genuine user on the target machine.
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Thanks to this requirement, security researchers told BleepingComputer that the vulnerability won’t be as widely abused as other privilege escalation vulnerabilities, such as PrintNightmare, which proved to be particularly troublesome for Microsoft to fix.
Security researcher Abdelhamid Naceri who discovered the vulnerability, and has written the PoC claims that it exists because Microsoft has failed to properly patch a previously reported vulnerability.
Tracked as CVE-2021-34484, Naceri claims that Microsoft only patched the symptom of the previous vulnerability, and not its root clause.
In a technical writeup, he claims that his PoC for the previous vulnerability manifested itself as an arbitrary directory deletion bug.
"Microsoft didn’t patch what was provided in the report but the impact of the PoC. Since the PoC I wrote before was horrible, it could only reproduce a directory deletion bug," claims Naceri.
After examining the fix, Naceri found that the patch was not sufficient and that he could still exploit the underlying vulnerability and elevate privileges.
Microsoft hasn’t yet publicly acknowledged the vulnerability, nor has it commented on Naceri’s claims. However, independent security researchers have tested Nasceri’s PoC and found it works as claimed.