Expert found a hardcoded SSH Key in Fortinet SIEM appliances

Expert found a hardcoded SSH public key in Fortinet ’s Security Information and Event Management FortiSIEM that can allow access to the FortiSIEM Supervisor. 

Andrew Klaus, a security specialist from Cybera, discovered a hardcoded SSH public key in Fortinet’s Security Information and Event Management FortiSIEM that can be used by attackers to the FortiSIEM Supervisor. 

The expert discovered that the Fortinet devices share the same SSH key for the user ‘tunneluser‘, and it is stored in plain text.

“FortiSIEM has a hardcoded SSH public key for user “tunneluser” which is the same between all installs. An attacker with this key can successfully authenticate as this user to the FortiSIEM Supervisor.” reads the security advisory. “The unencrypted key is also stored inside the FortiSIEM image. While the user’s shell is limited to running the /opt/phoenix/phscripts/bin/tunnelshell script, SSH authentication still succeeds.”

Fortinet published a security advisory for the issue that is tracked as CVE-2019-17659.

The vulnerability could be exploited by attackers to trigger a confition of denial of service. 

“A use of hard-coded cryptographic key vulnerability in FortiSIEM may allow a remote unauthenticated attacker to obtain SSH access to the supervisor as the restricted user “tunneluser” by leveraging knowledge of the private key from another installation or a firmware image.” reads the advisory.

The user ‘tunneluser‘ only runs in a restricted shell that lets only that user create tunnel connections from the supervisor to the originating IP.

The feature was implemented to enable connecting to collectors from the supervisor when there is a firewall between the collector and the supervisor.

Fortinet invites customers that are not using the reverse tunnel feature to disable SSH on port 19999 that only allows tunneluser to authenticate. Fortinet also advise customers to disable “tunneluser” SSH access on port 22.

Below the timeline of the vulnerability:

• Dec 2, 2019: Email sent to Fortinet PSIRT with vulnerability details.
• Dec 3, 2019: Automated reply from PSIRT that email was received.
• Dec 23, 2019: Sent a reminder email to PSIRT about requesting a human confirmation.
• Jan 3, 2019: Public Release.

The flaw affects FortiSIEM version 5.2.6 and below, the tech firm addressed it with the release of FortiSIEM version 5.2.7. 

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Pierluigi Paganini

(SecurityAffairs – FortiSIEM, hacking)

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