CVE-2025-33073

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 this means for your business

It affects Microsoft Windows. It matters if your company, or a supplier that handles your data, runs it.
Attackers are already using it. CISA added it to its list of flaws used in real attacks on 20 October 2025.
FIRST's prediction model gives it a 83% chance of attack attempts being seen in the next 30 days, ranking above 99% of all known flaws.

What to do

1Check whether your company or your suppliers run Microsoft Windows.
2If you do, follow CISA's required action below. No patch reference has been published yet.
3Treat it as urgent. US federal agencies must fix it by 10 November 2025. That deadline does not apply to private companies, but it shows how seriously CISA takes it.
4Because attackers have used it, check the affected systems for signs of a break-in, not only for the update.

Not sure if your company is exposed?

Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.

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Required action

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

CISA’s wording, unedited.

Scoring

CVSS: Not yet scored

Dates

Published: 2025-10-20
Added to KEV: 2025-10-20
Remediation due: 2025-11-10
Sources: CISA KEV