Last updated at Mon, 05 Jun 2023 14:47:19 GMT
Rapid7 is tracking reports of ongoing exploitation of CVE-2023-28771, a critical unauthenticated command injection vulnerability affecting multiple Zyxel networking devices.
The vulnerability is present in the default configuration of vulnerable devices and is exploitable in the Wide Area Network (WAN) interface, which is intended to be exposed to the internet. A VPN does not need to be configured on a device for it to be vulnerable. Successful exploitation of CVE-2023-28771 allows an unauthenticated attacker to execute code remotely on the target system by sending a specially crafted IKEv2 packet to UDP port 500 on the device.
Zyxel released an advisory for CVE-2023-28771 on April 25, 2023. On May 19, Rapid7 researchers published a technical analysis of the vulnerability on AttackerKB, underscoring the likelihood of exploitation.
As of May 19, there were at least 42,000 instances of Zyxel devices on the public internet. However, as Rapid7 researchers noted, this number only includes devices that expose their web interfaces on the WAN, which is not a default setting. Since the vulnerability is in the VPN service, which is enabled by default on the WAN, we expect the actual number of exposed and vulnerable devices to be much higher.
As of May 26, the vulnerability is being widely exploited, and compromised Zyxel devices are being leveraged to conduct downstream attacks as part of a Mirai-based botnet. Mirai botnets are frequently used to conduct DDoS attacks.
While CVE-2023-28771 is currently garnering large-scale threat actor attention, Zyxel published an advisory for two additional vulnerabilities — CVE-2023-33009 and CVE-2023-33010 — on May 24, 2023. CVE-2023-33009 and CVE-2023-33010 are buffer overflow vulnerabilities that can allow unauthenticated attackers to cause a DoS condition or execute arbitrary code on affected devices.
We strongly recommend that users of the affected Zyxel products update to the latest firmware on an emergency basis. At time of writing, the latest firmware version is 5.36 Patch 2, or 4.73 Patch 2 for ZyWALL/USG. See Zyxel’s advisory for additional details.
For InsightVM and Nexpose customers, a remote vulnerability check for CVE-2023-28771 has been available since the May 19, 2023 content release. Additional remote vulnerability checks for CVE-2023-33009 and CVE-2023-33010 are available in the May 31, 2023 content release.
Update May 31 12:45 PM ET: The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has now added CVE-2023-28771 to the Known Exploited Vulnerabilities (KEV) list.