Background exploitation KEV catalog No authentication

CVE-2023-33009

Zyxel Multiple Firewalls Buffer Overflow Vulnerability

CheckOps priority index

7.2/10 Patch within 7 days

Severity9.8

Probability2.8

Exploitation4/5

Severity = CVSS. Probability = EPSS (FIRST). Exploitation = public signals: KEV, EUVD, ransomware, EPSS above 10 %, no account required.

EPSS · today 28.1% higher than 98.1% of CVEs

CVSS 3.1 9.8 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:

Exploited for 1,247 days 05 Jun 2023

CISA due date 26 Jun 2023 for US federal agencies

Exploitation probability EPSS · FIRST

EPSS probability (%)Percentile among all CVEs

Exploitation signals 4 / 5

KEV catalog (CISA)05 Jun 2023
Exploited in EUVD (ENISA)05 Jun 2023
Used by ransomwareno
EPSS above 10 %28.1%
No account, over the networkyes

What to do

Fix

Apply the vendor’s fix as soon as it is available.

CISA guidance: Apply updates per vendor instructions.

Meanwhile

Take the service off the internet or restrict access to it, watch the logs and look for signs of compromise.

Manufacturers (CRA)

Exploited vulnerability in your product: early warning to ENISA within 24 h, then notification within 72 h (Article 14 of the Cyber Resilience Act). The CRA explained

Description ENISA EUVD

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.

Affected products

ATP series firmwareUSG FLEX series firmwareUSG FLEX 50(W) firmwareZyWALL/USG series firmwareVPN series FirmwareUSG20(W)-VPN firmwareMultiple Firewalls

Affected versions

4.60 through 5.36 Patch 1
4.60 through 4.73 Patch 1

Weaknesses (CWE)

CWE-120

Open source packages OSV

Affected libraries according to OSV, with fixed versions.

Timeline

24 May 2023
Published
05 Jun 2023
Exploitation reported (ENISA)
05 Jun 2023
Added to the KEV catalog
26 Jun 2023
CISA remediation due date
26 Sept 2026
EPSS peak: 28.1%

References

Other exploited vulnerabilities from the same vendor

CVE-2026-7273Zyxel GS1900 Series Switches Stack-Based Buffer Overflow Vulnerability
4.8 · Actively exploited
CVE-2024-40891Zyxel DSL CPE OS Command Injection Vulnerability
6.0 · Background exploitation
CVE-2024-40890Zyxel DSL CPE OS Command Injection Vulnerability
5.9 · Background exploitation
CVE-2024-11667Zyxel Multiple Firewalls Path Traversal Vulnerability
5.5 · Background exploitation
CVE-2017-6884Zyxel EMG2926 Routers Command Injection Vulnerability
6.9 · Background exploitation
CVE-2017-18368Zyxel P660HN-T1A Routers Command Injection Vulnerability
9.2 · Background exploitation