Microsoft Task Scheduler: privilege escalation flaw under attack

What is affected

Microsoft Task Scheduler is mostly run by companies, schools and public bodies, not on home computers. You are unlikely to have it yourself, but organisations that hold your data may. Breaches that start with flaws like this one are how personal data ends up leaked.

A privilege escalation vulnerability exists in the way the Task Scheduler Service validates certain file operations.

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

Needs access to the device or a file opened on it

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. At home: nothing to install. Keep your own devices updated and use a different password for every service, so that a breach at one organisation does not open your other accounts.
2. If you administer Microsoft Task Scheduler at work: apply the vendor's fix or mitigation now and review logs for signs of compromise, because the flaw was being exploited before it was listed.
3. If the product is past its support date and no fix exists, take it off the internet or retire it.

Apply updates per vendor instructions.

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on March 15, 2022, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by April 5, 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 6.1% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 93% of all scored vulnerabilities.

Its CVSS severity score is 7.8 out of 10 (high), as recorded in the US National Vulnerability Database.

Technical description

An elevation of privilege vulnerability exists in the way the Task Scheduler Service validates certain file operations. An attacker who successfully exploited the vulnerability could gain elevated privileges on a victim system. To exploit the vulnerability, an attacker would require unprivileged code execution on a victim system. The security update addresses the vulnerability by correctly validating file operations.