Microsoft Windows: privilege escalation flaw under attack

What is affected

Microsoft Windows is found on ordinary personal computers and phones, so this is not only a problem for companies. If you use it and have not updated since the fix was released, you are exposed.

Microsoft Windows Active Directory contains a privilege escalation vulnerability due to the way it distributes passwords that are configured using Group Policy preferences. An authenticated attacker who successfully exploits the vulnerability could decrypt the passwords and use them to elevate privileges on the domain.

What an attacker can do

This is a privilege escalation flaw. It lets an attacker turn limited access into full administrator control. Attackers pair it with another flaw or a malicious file: once anything of theirs runs on the device, this bug lets it take over completely.

How it is reached

Over the internet or network

Access the attacker needs

A basic user account

Does the victim have to do something?

No, works without the victim doing anything

CISA records this vulnerability as known to be used in ransomware campaigns: attackers use it to get in, then encrypt files and demand payment.

What to do

1. Update Microsoft Windows now. Open the update or "About" screen, install whatever is offered and restart the app or device, because the fix is not active until you do.
2. Turn on automatic updates so the next fix arrives without you having to look for it.
3. If your device is too old to receive this update, stop using the affected app for anything sensitive and plan a replacement.

Apply updates per vendor instructions.

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on November 3, 2021, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by May 3, 2022, a deadline that has already passed. That deadline does not bind anyone else, but it shows how seriously the agency rates it.

The EPSS model estimates a 65% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 99.2% of all scored vulnerabilities.

Its CVSS severity score is 8.8 out of 10 (high), as recorded in the US National Vulnerability Database.

Technical description

The Group Policy implementation in Microsoft Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8, Windows 8.1, and Windows Server 2012 Gold and R2 does not properly handle distribution of passwords, which allows remote authenticated users to obtain sensitive credential information and consequently gain privileges by leveraging access to the SYSVOL share, as exploited in the wild in May 2014, aka "Group Policy Preferences Password Elevation of Privilege Vulnerability."