CVE-2023-28771
Zyxel Multiple Firewalls OS Command Injection Vulnerability
Zyxel Multiple Firewalls
Improper error message handling in Zyxel ZyWALL/USG series firmware versions 4.60 through 4.73, VPN series firmware versions 4.60 through 5.35, USG FLEX series firmware versions 4.60 through 5.35, and ATP series firmware versions 4.60 through 5.35, which could allow an unauthenticated attacker to execute some OS commands remotely by sending crafted packets to an affected device.
Exploitation status
CISA Known Exploited Vulnerabilities
Listed by CISA on 31 May 2023. US federal agencies were required to remediate it by 21 June 2023.
EPSS — exploitation probability
FIRST puts the probability of exploitation activity in the next 30 days at 99.3%, which is higher than 99.9% of all scored vulnerabilities. EPSS is a forecast of activity, not a measure of severity, and it is rescored daily.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Frequently asked questions
Is CVE-2023-28771 being exploited by ransomware groups?
No ransomware group in this database is currently recorded as exploiting CVE-2023-28771.
What does CVE-2023-28771 affect?
CVE-2023-28771 affects Zyxel Multiple Firewalls. Improper error message handling in Zyxel ZyWALL/USG series firmware versions 4.60 through 4.73, VPN series firmware versions 4.60 through 5.35, USG FLEX series firmware versions 4.60 through 5.35, and ATP series firmware versions 4.60 through 5.35, which could allow an unauthenticated attacker to execute some OS commands remotely by sending crafted packets to an affected device.
How severe is CVE-2023-28771?
CVE-2023-28771 is rated CRITICAL with a CVSS base score of 9.8. EPSS puts the probability of exploitation in the next 30 days at 99.3%, higher than 99.9% of all scored vulnerabilities. It is listed in the CISA Known Exploited Vulnerabilities catalog, with a federal remediation deadline of 21 June 2023.
How should organisations respond to CVE-2023-28771?
Apply the vendor patch for Zyxel Multiple Firewalls as the first priority, and treat any internet-facing instance as the most urgent. Because this vulnerability is associated with ransomware activity, also review whether the affected systems were reachable before patching, rather than assuming that patching alone closes the incident.