Background exploitation KEV catalog No authentication

CVE-2023-28771

Zyxel Multiple Firewalls OS Command Injection Vulnerability

CheckOps priority index

9.3/10 Patch within 24 h

Severity9.8

Probability9.9

Exploitation4/5

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

EPSS · today 99.3% higher than 99.9% of CVEs

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

Exploited for 1,252 days 31 May 2023

CISA due date 21 Jun 2023 for US federal agencies

Exploitation probability EPSS · FIRST

EPSS probability (%)Percentile among all CVEs

Exploitation signals 4 / 5

KEV catalog (CISA)31 May 2023
Exploited in EUVD (ENISA)31 May 2023
Used by ransomwareno
EPSS above 10 %99.3%
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

Improper error message handling in Zyxel ZyWALL/USG series firmware versions 4.60 through 4.73, VPN series firmware versions 4.60 through 5.35, USG FLEX series firmware versions 4.60 through 5.35, and ATP series firmware versions 4.60 through 5.35, which could allow an unauthenticated attacker to execute some OS commands remotely by sending crafted packets to an affected device.

Affected products

USG FLEX series firmwareVPN series FirmwareATP series firmwareZyWALL/USG series firmwareMultiple Firewalls

Affected versions

4.60 through 5.35
4.60 through 4.73

Weaknesses (CWE)

CWE-78

Open source packages OSV

Affected libraries according to OSV, with fixed versions.

Timeline

25 Apr 2023
Published
31 May 2023
Exploitation reported (ENISA)
31 May 2023
Added to the KEV catalog
21 Jun 2023
CISA remediation due date
26 Sept 2026
EPSS peak: 99.3%

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