Zyxel fixed a critical RCE flaw in its firewall devices and urges customers to install the patches
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2023-27991 +1 in the same advisory: …27990 | The post-authentication command injection vulnerability in the CLI command of Zyxel ATP series firmware versions 4.32 through 5.35, USG FLEX series firmware ver The post-authentication command injection vulnerability in the CLI command of Zyxel ATP series firmware versions 4.32 through 5.35, USG FLEX series firmware versions 4.50 through 5.35, USG FLEX 50(W) firmware versions 4.16 through 5.35, USG20(W)-VPN firmware versions 4.16 through 5.35, and VPN series firmware versions 4.30 through 5.35, which could allow an authenticated attacker to execute some OS commands remotely. NVD description · AI analysis pending | 8.8 group max | 1% |
| — | ||
| CVE-2023-28771 | Unauthenticated OS Command Injection in Zyxel ATP, USG FLEX, VPN, and ZyWALL Firewalls CVE-2023-28771 is an unauthenticated OS command injection flaw (CWE-78) in Zyxel firewall firmware, caused by improper error message handling in the IKE packet decoder. A remote attacker triggers it by sending crafted packets to an affected device, with no credentials or user interaction required (CVSS 3.1: 9.8, network vector, low complexity). Successful exploitation lets the attacker execute operating-system commands on the firewall, which typically means full device compromise of these perimeter/VPN gateway appliances. Organizations running Zyxel ZyWALL/USG, VPN, USG FLEX, or ATP series firewalls on the affected firmware ranges are exposed, especially where IKE/VPN traffic is reachable from the internet. Exploitation is confirmed in the wild: the flaw was added to CISA's KEV on 2023-05-31, carries a 99.3% EPSS score (100th percentile), is reportedly used by DDoS botnets, and was reportedly exploited in the May 2023 coordinated attacks against nearly two dozen Danish energy companies. Do: Apply Zyxel's patched firmware to all affected devices per the vendor advisory - releases newer than 4.73 for ZyWALL/USG and newer than 5.35 for ATP, USG FLEX, and VPN series - prioritizing internet-facing and VPN gateway appliances, as this is a KEV required-action vulnerability. Where immediate patching is not possible, restrict IKE traffic (UDP 500/4500) to trusted peers or disable unneeded IPsec VPN termination. After patching, review device logs and configurations for signs of command execution or unexpected changes, given confirmed botnet and targeted-attack use. | 9.8 | 99% | KEV PoC |
| largetens of thousands of internet-exposed Zyxel firewall/VPN gateways (order of 10,000-100,000 devices/sites); estimate |
Full article392 words · extracted from securityaffairs.com · click to collapse
A vulnerability impacting Zyxel firewalls, tracked as CVE-2023-28771, can be exploited to execute arbitary code on vulnerable devices.
Researchers from TRAPA Security have discovered a critical remote code execution vulnerability, tracked as CVE-2023-28771 (CVSS score 9.8), impacting Zyxel Firewall.
The vulnerability is an 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. A remote, unauthenticated attacker can trigger the flaw by sending specially crafted packets to a vulnerable device and execute some OS commands remotely.
Zyxel has released security patches to address the vulnerability and urges customers to install them.
“Improper error message handling in some firewall versions could allow an unauthenticated attacker to execute some OS commands remotely by sending crafted packets to an affected device.” reads the advisory published by the vendor.
The company also fixed a high-severity post-authentication command injection issue (CVE-2023-27991, CVSS score: 8.8) affecting some specific firewall versions.
The vulnerability resides in the CLI command of Zyxel ATP series firmware versions 4.32 through 5.35, USG FLEX series firmware versions 4.50 through 5.35, USG FLEX 50(W) firmware versions 4.16 through 5.35, USG20(W)-VPN firmware versions 4.16 through 5.35, and VPN series firmware versions 4.30 through 5.35. The vulnerability can be exploited by a remote, authenticated attacker to execute some OS commands.
The last vulnerability addressed by the company is an XSS vulnerability, tracked as CVE-2023-27990, that affects some firewall versions.
“The XSS vulnerability in some firewall versions could allow an authenticated attacker with administrator privileges to store malicious scripts in a vulnerable device.” reads the advisory published by the vendor. “A successful XSS attack could then result in the stored malicious scripts being executed when the user visits the Logs page of the GUI on the device.”
Both CVE-2023-27990 and CVE-2023-27991 were reported by Alessandro Sgreccia from Tecnical Service SRL.
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