CVE-2023-33009A buffer overflow vulnerability in the notification function in Zyxel ATP series firmware versions 4.60 through 5.36 Patch 1, USG FLEX…
- 9.8CriticalCVSS base score
- 28.1%Exploitation in 30 daysEPSS · top 1.9% of all CVEs
- YesKnown exploitedin CISA's KEV since 5 Jun 2023
- YesPublic exploitsa reference or SSVC says so
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.
Exploited in the wild
CISA lists this vulnerability in its Known Exploited Vulnerabilities catalog as Zyxel Multiple Firewalls Buffer Overflow Vulnerability.
- Added
- 5 Jun 2023
- Fix due (US federal)
- 26 Jun 2023
- Used by ransomware
- Not known
Apply updates per vendor instructions.
ENISA's EU Vulnerability Database lists it as exploited, from CISA's KEV, since 5 Jun 2023.
Public exploit
An exploit or proof of concept is public: anyone can try it against an unpatched system. CISA's SSVC rates its exploitation: it is being exploited.
Timeline
ID reserved
By Zyxel
- 7 days later
· 7 days later
Published
- 12 days later
· 12 days later
Added to CISA KEV
Known exploited in the wild
- 2 years later
· 2 years later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| ZyxelCNA (assigner) | 3.1 | Critical9.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
| NVDNVD · Analyzed | 3.1 | Critical9.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
- EPSS (exploitation in 30 days)
- 28.1% · top 1.9% of all CVEs (12 Nov 2026)
- CISA SSVC
- Exploitation: active · Automatable: yes · Technical impact: total
The list uses the assigner's score when there is one, then CISA's, then NVD's: Critical 9.8.
Affected products
- affected 4.60 through 5.36 Patch 1
Zyxel · USG FLEX series firmware
- affected 4.60 through 5.36 Patch 1
Zyxel · USG FLEX 50(W) firmware
- affected 4.60 through 5.36 Patch 1
- affected 4.60 through 5.36 Patch 1
- affected 4.60 through 5.36 Patch 1
Zyxel · ZyWALL/USG series firmware
- affected 4.60 through 4.73 Patch 1
References
References2
- https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-multiple-buffer-overflow-vulnerabilities-of-firewalls (opens in a new tab)x_transferred
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-33009 (opens in a new tab)government-resource
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- CISA KEV catalog (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2023-37198 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2023-33009)Record last updated .