FBI: APTs Actively Exploiting Fortinet VPN Security Holes

fortinet vpn cyberattacks

Three security vulnerabilities in the Fortinet SSL VPN are being used to gain a foothold within networks before moving laterally and carrying out recon.


The FBI and the Cybersecurity and Infrastructure Security Agency are warning that advanced persistent threat (APT) nation-state actors are actively exploiting known security vulnerabilities in the Fortinet FortiOS cybersecurity operating system, affecting the company’s SSL VPN products.

According to an alert issued Friday by the FBI and CISA, cyberattackers are scanning devices on ports 4443, 8443 and 10443, looking for unpatched Fortinet security implementations. Specifically, APTs are exploiting CVE-2018-13379, CVE-2019-5591 and CVE-2020-12812.

“It is likely that the APT actors are scanning for these vulnerabilities to gain access to multiple government, commercial and technology services networks,” according to the alert. “APT actors have historically exploited critical vulnerabilities to conduct distributed denial-of-service (DDoS) attacks, ransomware attacks, structured query language (SQL) injection attacks, spear-phishing campaigns, website defacements, and disinformation campaigns.”

The bug tracked as CVE-2018-13379 is a path-traversal issue in Fortinet FortiOS, where the SSL VPN web portal allows an unauthenticated attacker to download system files via specially crafted HTTP resource requests.

The CVE-2019-5591 flaw is a default-configuration vulnerability in FortiOS that could allow an unauthenticated attacker on the same subnet to intercept sensitive information by impersonating the LDAP server.

And finally, CVE-2020-12812 is an improper-authentication vulnerability in SSL VPN in FortiOS, which could allow a user to log in successfully without being prompted for the second factor of authentication (FortiToken) if they changed the case of their username.

“Attackers are increasingly targeting critical external applications – VPNs have been targeted even more this last year,” said Zach Hanley, senior red team engineer at Horizon3.AI, via email. “These three vulnerabilities targeting the Fortinet VPN allow an attacker to obtain valid credentials, bypass multifactor authentication (MFA), and man-in-the-middle (MITM) authentication traffic to intercept credentials.”

Hanley added, “The common theme here is: once they are successful, they will look just like your normal users.”

The bugs are popular with cyberattackers in general, due to Fortinet’s widespread footprint, researchers noted.

“CVE-2018-13379 is a critical vulnerability in the Fortinet FortiOS SSL VPN that has been favored by cybercriminals since exploit details became public in August 2019,” Satnam Narang, staff research engineer at Tenable, said via email. “In fact, Tenable’s 2020 Threat Landscape Retrospective placed it in our Top 5 Vulnerabilities of 2020 because we see threat actors continue to leverage it in the wild, well over a year after it was first disclosed.”

The FBI and CISA didn’t specify which APTs are mounting the recent activity.

“The security of our customers is our first priority,” according to a statement from Fortinet provided to Threatpost. “For example, CVE-2018-13379 is an old vulnerability resolved in May 2019. Fortinet immediately issued a PSIRT advisory and communicated directly with customers and via corporate blog posts on multiple occasions in August 2019 and July 2020 strongly recommending an upgrade. Upon resolution we have consistently communicated with customers as recently as late as 2020. CVE-2019-5591 was resolved in July 2019 and CVE-2020-12812 was resolved in July 2020. To get more information, please visit our blog and immediately refer to the May 2019 advisory. If customers have not done so, we urge them to immediately implement the upgrade and mitigations.”

Initial Compromise & Recon

Once exploited, the attackers are moving laterally and carrying out reconnaissance on targets, according to officials.

“The APT actors may be using any or all of these CVEs to gain access to networks across multiple critical-infrastructure sectors to gain access to key networks as pre-positioning for follow-on data exfiltration or data encryption attacks,” the warning explained. “APT actors may use other CVEs or common exploitation techniques—such as spear-phishing—to gain access to critical infrastructure networks to pre-position for follow-on attacks.”

The joint cybersecurity advisory from the FBI and CISA follows last year’s flurry of advisories from U.S. agencies about APT groups using unpatched vulnerabilities to target federal agencies and commercial organizations. For instance, in October an alert went out that APTs were using flaws in outdated VPN technologies from Fortinet, Palo Alto Networks and Pulse Secure to carry out cyberattacks on targets in the United States and overseas.

“It’s no surprise to see additional Fortinet FortiOS vulnerabilities like CVE-2019-5591 and CVE-2020-12812 added to the list of known, but unpatched flaws being leveraged by these threat actors,” said Narang. “Over the last few years, SSL VPN vulnerabilities have been an attractive target for APT groups and cybercriminals alike. With the shift to remote work and the increased demand for SSL VPNs like Fortinet and others, the attack surface and available targets have expanded. Organizations should take this advisory seriously and prioritize patching their Fortinet devices immediately if they haven’t done so already.”

How Can I Protect My Network from Cyberattacks?

The FBI and CISA suggest a range of best practices to help organizations thwart these and other attacks:

  • Immediately patch CVEs 2018-13379, 2020-12812 and 2019-5591.
  • If FortiOS is not used by your organization, add key artifact files used by FortiOS to your organization’s execution-deny list. Any attempts to install or run this program and its associated files should be prevented.
  • Regularly back up data, air-gap and password-protect backup copies offline. Ensure copies of critical data are not accessible for modification or deletion from the primary system where the data resides.
  • Implement network segmentation.
  • Require administrator credentials to install software.
  • Implement a recovery plan to restore sensitive or proprietary data from a physically separate, segmented, secure location (e.g., hard drive, storage device, the cloud).
  • Install updates/patch operating systems, software, and firmware as soon as updates/patches are released.
  • Use multifactor authentication where possible.
  • Regularly change passwords to network systems and accounts, and avoid reusing passwords for different accounts. Implement the shortest acceptable timeframe for password changes.
  • Disable unused remote access/Remote Desktop Protocol (RDP) ports and monitor remote access/RDP logs.
  • Audit user accounts with administrative privileges and configure access controls with least privilege in mind.
  • Install and regularly update antivirus and anti-malware software on all hosts.
  • Consider adding an email banner to emails received from outside your organization.
  • Disable hyperlinks in received emails.
  • Focus on awareness and training. Provide users with training on information security principles and techniques, particularly on recognizing and avoiding phishing emails.

This story was updated at 2:30 p.m. ET on April 7, to include a statement from Fortinet.

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