Enlarge

Hackers working for the Chinese government gained access to more than 20,000 VPN appliances sold by Fortinet using a critical vulnerability that the company failed to disclose for two weeks after fixing it, Netherlands government officials said.

The vulnerability, tracked as CVE-2022-42475, is a heap-based buffer overflow that allows hackers to remotely execute malicious code. It carries a severity rating of 9.8 out of 10. A maker of network security software, Fortinet silently fixed the vulnerability on November 28, 2022, but failed to mention the threat until December 12 of that year, when the company said it became aware of an “instance where this vulnerability was exploited in the wild.” On January 11, 2023—more than six weeks after the vulnerability was fixed—Fortinet warned a threat actor was exploiting it to infect government and government-related organizations with advanced custom-made malware.

Enter CoatHanger

The Netherlands officials first reported in February that Chinese state hackers had exploited CVE-2022-42475 to install an advanced and stealthy backdoor tracked as CoatHanger on Fortigate appliances inside the Dutch Ministry of Defense. Once installed, the never-before-seen malware, specifically designed for the underlying FortiOS operating system, was able to permanently reside on devices even when rebooted or receiving a firmware update. CoatHanger could also escape traditional detection measures, the officials warned. The damage resulting from the breach was limited, however, because infections were contained inside a segment reserved for non-classified uses.