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Actively exploited vulnerability

Microsoft Skype for Business: privilege escalation flaw under attack

CVE-2023-41763 · Microsoft Skype for Business Privilege Escalation Vulnerability

Concerns everyone who uses it5.3 medium

What is affected

Microsoft Skype for Business 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 Skype for Business contains an unspecified vulnerability that allows for privilege escalation.

CISA's description

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
No account needed
Does the victim have to do something?
No, works without the victim doing anything

What to do

  1. Update Microsoft Skype for Business 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 or discontinue use of the product if mitigations are unavailable.

Action required by CISA for US federal agencies

Vendor advisories and fixes

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on October 10, 2023, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by October 31, 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 90% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 99.8% of all scored vulnerabilities.

Its CVSS severity score is 5.3 out of 10 (medium), as recorded in the US National Vulnerability Database.

Technical description

Skype for Business Elevation of Privilege Vulnerability

NIST National Vulnerability Database
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