VMware Tools: authentication bypass flaw under attack

What is affected

VMware Tools 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.

VMware Tools contains an authentication bypass vulnerability in the vgauth module. A fully compromised ESXi host can force VMware Tools to fail to authenticate host-to-guest operations, impacting the confidentiality and integrity of the guest virtual machine. An attacker must have root access over ESXi to exploit this vulnerability.

What an attacker can do

This is a authentication bypass flaw. It lets an attacker get in without a valid username and password and act as a legitimate user, often as an administrator.

How it is reached

Needs access to the device or a file opened on it

Access the attacker needs

An administrator account

Does the victim have to do something?

No, works without the victim doing anything

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 VMware Tools 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.

Vendor advisories and fixes

• vmware.comwww.vmware.com/security/advisories/VMSA-2023-0013.html

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on June 23, 2023, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by July 14, 2023, 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 14% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 96% of all scored vulnerabilities.

Its CVSS severity score is 3.9 out of 10 (low), as recorded in the US National Vulnerability Database.

Technical description

A fully compromised ESXi host can force VMware Tools to fail to authenticate host-to-guest operations, impacting the confidentiality and integrity of the guest virtual machine.