Cring ransomware operators are exploiting an old path traversal vulnerability in the FortiOS SSL VPN web portal to gain access to enterprise networks, Kaspersky warns.
At the beginning of 2021, the threat actors behind the Cring ransomware were observed launching numerous attacks on European industrial enterprises, forcing at least one organization to shut down a production site.
The initial vector of attack was later identified as CVE-2018-13379, a vulnerability in the FortiOS SSL VPN web portal that could allow unauthenticated attackers to download FortiOS system files.
The directory traversal vulnerability can be exploited to extract the session file of the VPN Gateway, thus allowing unauthenticated attackers to gain access to usernames and plaintext passwords.
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The attacks observed by Kaspersky started with test connections to the VPN Gateway, to check the software version on the target devices, followed by the main attack phase several days later.
“The attackers may have identified the vulnerable device themselves by scanning IP addresses. Alternatively, they may have bought a ready-made list containing IP addresses of vulnerable Fortigate VPN Gateway devices,” Kaspersky notes.
After gaining initial access to the enterprise network, the attackers deployed credential harvesting utilities that allowed them to compromise the domain administrator account. Next, they deployed the Cobalt Strike backdoor to take control of the infected systems, followed by the Cring ransomware.
“Various details of the attack indicate that the attackers had carefully analyzed the infrastructure of the attacked organization and prepared their own infrastructure and toolset based on the information collected at the reconnaissance stage,” Kaspersky says.
In May 2019, Fortinet issued an advisory to inform customers about the availability of patches for CVE-2018-13379, yet many systems remain unpatched and threat actors continue to exploit this state of facts for their own benefit.
In fact, the FBI and CISA issued an alert last week to warn governmental, commercial, and technology services organizations about attacks targeting multiple vulnerabilities in FortiOS. Fortinet too once again urged customers to apply the available patches, to remain protected from attacks.
In addition to ensuring their SSL VPN Gateway is up to date, organizations are advised to change the active directory policy using the principle of least privilege, restrict VPN access, and keep systems backed up and periodically verify the integrity of backups.
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