CVE-2023-33009
Published: June 5, 2023
Official Description
Zyxel ATP, USG FLEX, USG FLEX 50(W), USG20(W)-VPN, VPN, and ZyWALL/USG firewalls contain a buffer overflow vulnerability in the notification function that could allow an unauthenticated attacker to cause denial-of-service (DoS) conditions and remote code execution on an affected device.
CISA KEV Advisory
Zyxel Multiple Firewalls Buffer Overflow Vulnerability
Zyxel ATP, USG FLEX, USG FLEX 50(W), USG20(W)-VPN, VPN, and ZyWALL/USG firewalls contain a buffer overflow vulnerability in the notification function that could allow an unauthenticated attacker to cause denial-of-service (DoS) conditions and remote code execution on an affected device.
Apply updates per vendor instructions.
Risk Analysis
This buffer overflow vulnerability in Zyxel ATP, USG FLEX, USG FLEX 50(W), USG20(W)-VPN, VPN, and ZyWALL/USG firewalls' notification function allows an unauthenticated attacker to cause denial-of-service (DoS) conditions and remote code execution. It is a high-severity flaw and is urgent due to its inclusion in CISA's KEV catalog, confirming active exploitation. The EPSS score of 0.06174 indicates a moderate likelihood of exploitation.
This vulnerability is actively exploited in the wild and is listed in CISA's KEV catalog, confirming its use by attackers. It is remotely exploitable by an unauthenticated attacker.
Apply available patches and firmware updates for all affected Zyxel ATP, USG FLEX, USG FLEX 50(W), USG20(W)-VPN, VPN, and ZyWALL/USG firewalls. Ensure firewalls are configured with strong access controls and are regularly updated.
Technical Analysis
CVE-2023-33009 requires local access, meaning attackers must already have a foothold on the target system.
Exploitation requires some privileges, which limits the exposure to scenarios where an attacker has already gained initial access.
CISA has added CVE-2023-33009 to the Known Exploited Vulnerabilities (KEV) catalog, confirming active exploitation in the wild. U.S. federal agencies are required to patch this within the mandated timeframe, and all organizations should treat remediation as urgent.
Exploit & PoC Resources
All References (2)
Quick Facts
Recommended Actions
- →Apply vendor patches immediately
- →Monitor CVE-2023-33009 in threat intel feeds
- →Review IDS/IPS signatures for exploitation attempts
- !CISA KEV: Federal agencies must patch per BOD 22-01 timeline
- !Active exploitation confirmed — treat as P1