Microsoft Windows: improper access control 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 SMB Client contains an improper access control vulnerability that could allow for privilege escalation. An attacker could execute a specially crafted malicious script to coerce the victim machine to connect back to the attack system using SMB and authenticate.

What an attacker can do

This is a improper access control flaw. It lets an attacker perform actions or reach data that should be restricted to authorised users.

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

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 mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Vendor advisories and fixes

• msrc.microsoft.commsrc.microsoft.com/update-guide/en-US/advisory/CVE-2025-33073

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on October 20, 2025, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by November 10, 2025, 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 83% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 99.7% 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

Improper access control in Windows SMB allows an authorized attacker to elevate privileges over a network.