Fortinet FortiOS: authentication bypass flaw under attack

What is affected

Fortinet FortiOS 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.

Fortinet FortiOS contains a use of hard-coded credentials vulnerability that could allow an attacker to cipher sensitive data in FortiOS configuration backup file via knowledge of the hard-coded key.

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

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

CISA records this vulnerability as known to be used in ransomware campaigns: attackers use it to get in, then encrypt files and demand payment.

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 Fortinet FortiOS 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 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

• fortiguard.comfortiguard.com/advisory/FG-IR-19-007

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on June 25, 2025, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by July 16, 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 5.8% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 93% of all scored vulnerabilities.

Its CVSS severity score is 6.5 out of 10 (medium), as recorded in the US National Vulnerability Database.

Technical description

Use of a hard-coded cryptographic key to cipher sensitive data in FortiOS configuration backup file may allow an attacker with access to the backup file to decipher the sensitive data, via knowledge of the hard-coded key. The aforementioned sensitive data includes users' passwords (except the administrator's password), private keys' passphrases and High Availability password (when set).