CVE-2023-33009: Zyxel Multiple Firewalls Buffer Overflow Vulnerability

Vulnerability summary

CVE-2023-33009 is a critical (CVSS 9.8) Classic Buffer Overflow vulnerability in Zyxel Multiple Firewalls. It is known to be exploited: CISA lists it, first on 05-06-2023. EPSS estimates a 28.14% chance of exploitation in the next 30 days, higher than 98% of scored vulnerabilities.

Timeline

1. 24-05-2023
   PublishedVulnerability first disclosed.
2. 05-06-2023
   Added to CISA KEVZyxel Multiple Firewalls Buffer Overflow Vulnerability
3. 26-06-2023
   CISA remediation dueApply updates per vendor instructions.
4. 21-10-2025
   Last modifiedVulnerability information updated.

Description

A buffer overflow vulnerability in the notification function in Zyxel ATP series firmware versions 4.60 through 5.36 Patch 1, USG FLEX series firmware versions 4.60 through 5.36 Patch 1, USG FLEX 50(W) firmware versions 4.60 through 5.36 Patch 1, USG20(W)-VPN firmware versions 4.60 through 5.36 Patch 1, VPN series firmware versions 4.60 through 5.36 Patch 1, ZyWALL/USG series firmware versions 4.60 through 4.73 Patch 1, could allow an unauthenticated attacker to cause denial-of-service (DoS) conditions and even a remote code execution on an affected device.

• CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer.