CVE-2023-28771 on CISA KEV

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 unauthenti

01What CISA says about this vulnerability

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.

02Required action — verbatim from CISA

Apply updates per vendor instructions.

03Notes & references

• www.zyxel.com — https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advis…
• packetstormsecurity.com — http://packetstormsecurity.com/files/172820/Zyxel-IKE-Packet-Decoder-Unauthentic…

04SARA's analyst layer — why this matters

This vulnerability is currently on the CISA KEV list, which CISA only adds CVEs to when there is reliable evidence of active exploitation in the wild. For federal civilian agencies, BOD 22-01 requires remediation by the due date above. For everyone else, KEV is the strongest "patch immediately" signal you can get from public threat intel.

05Affected products (summary)

Vendor	Product	Versions
Zyxel	ZyWALL/USG series firmware	4.60 through 4.73
Zyxel	VPN series firmware	4.60 through 5.35
Zyxel	USG FLEX series firmware	4.60 through 5.35
Zyxel	ATP series firmware	4.60 through 5.35

06Detection

Open the Sigma generator with a pre-filled prompt for this CVE to draft a starting detection:

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