CVE-2019-5591

What this means for your business

• It affects Fortinet FortiOS. 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 3 November 2021.
• Ransomware gangs are known to have used it.
• An attacker can use it from inside the same network, without a login, and without anyone at your company clicking anything.
• FIRST's prediction model gives it a 18% chance of attack attempts being seen in the next 30 days, ranking above 97% of all known flaws.

What to do

1. 1Check whether your company or your suppliers run Fortinet FortiOS, and which version. The affected versions are listed further down this page.
2. 2If you do, apply the vendor's fix. A patch or vendor advisory has been published.
3. 3Treat it as urgent. US federal agencies must fix it by 3 May 2022. That deadline does not apply to private companies, but it shows how seriously CISA takes it.
4. 4Because attackers have used it, check the affected systems for signs of a break-in, not only for the update.