CVE-2023-33009: Zyxel Multiple Firewalls Buffer Overflow Vulnerability
- Is it exploited?
Yes. CISA added it to the Known Exploited Vulnerabilities catalog on , 12 days after the CVE record was published.
- How likely is exploitation in the next 30 days?
- 28.1%
EPSS score, percentile 98.1 of all scored records
- How severe?
- 9.8 Critical
CVSS v3.1 base score, given by the CNA
- What should I do?
CISA deadline . Apply updates per vendor instructions.
The CVE record links no vendor advisory, patch or mitigation.
- Which versions are affected?
Affected
- 4.60 through 5.36 Patch 1
- 4.60 through 5.36 Patch 1
- 4.60 through 5.36 Patch 1
- 4.60 through 5.36 Patch 1
- 4.60 through 5.36 Patch 1
- 4.60 through 4.73 Patch 1
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of ; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of ; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.
What to do
Required action, set by CISA
Apply updates per vendor instructions.
CISA due date for this action: .
Advisories and patches
The CVE record links no vendor advisory, patch or mitigation.
Linked from CISA's catalog entry
- https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-multiple-buffer-overflow-vulnerabilities-of-firewalls
- https://nvd.nist.gov/vuln/detail/CVE-2023-33009
Affected products and versions
As listed in the CVE record.
| Status | Versions |
|---|---|
| Affected | 4.60 through 5.36 Patch 1 |
Versions not listed are: unaffected.
| Status | Versions |
|---|---|
| Affected | 4.60 through 5.36 Patch 1 |
Versions not listed are: unaffected.
| Status | Versions |
|---|---|
| Affected | 4.60 through 5.36 Patch 1 |
Versions not listed are: unaffected.
| Status | Versions |
|---|---|
| Affected | 4.60 through 5.36 Patch 1 |
Versions not listed are: unaffected.
| Status | Versions |
|---|---|
| Affected | 4.60 through 5.36 Patch 1 |
Versions not listed are: unaffected.
| Status | Versions |
|---|---|
| Affected | 4.60 through 4.73 Patch 1 |
Versions not listed are: unaffected.
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.
About this 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.
Summary: CISA's KEV catalog, as of .
- CISA added CVE-2023-33009 to its Known Exploited Vulnerabilities (KEV) catalog on 5 Jun 2023.
- CISA's ransomware flag for this entry is "Unknown": no evidence of ransomware use in the catalog, which is not proof of none.
- The due date CISA sets for the required action is 26 Jun 2023.
- The CVE record was published on 24 May 2023, 12 days before it was added to KEV.
- The CVE record carries a CVSS v3.1 base score of 9.8 (Critical), given by its CNA.
- FIRST's EPSS model puts the probability of exploitation in the next 30 days at 28.1% (percentile 98.1), as of 28 Oct 2026.
- CISA's SSVC assessment in the CVE record: exploitation active, automatable yes, technical impact total.
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of ; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of ; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of . About the data.
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.
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.
Weakness
- CWE-120: Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.
Timeline
| Date | Event |
|---|---|
| CVE record published | |
| Added to CISA KEV | |
| CISA due date for the required action | |
| CVE record last updated |
References
More exploited Zyxel vulnerabilities
- CVE-2026-7273: Zyxel GS1900 Series Switches Stack-Based Buffer Overflow Vulnerability
- CVE-2024-40890: Zyxel DSL CPE OS Command Injection Vulnerability
- CVE-2024-40891: Zyxel DSL CPE OS Command Injection Vulnerability
- CVE-2024-11667: Zyxel Multiple Firewalls Path Traversal Vulnerability
- CVE-2017-6884: Zyxel EMG2926 Routers Command Injection Vulnerability
- CVE-2017-18368: Zyxel P660HN-T1A Routers Command Injection Vulnerability