CVE-2023-22913 in USG FLEX
Summary
by MITRE • 04/24/2023
A post-authentication command injection vulnerability in the “account_operator.cgi” CGI program of Zyxel USG FLEX series firmware versions 4.50 through 5.35, and VPN series firmware versions 4.30 through 5.35, which could allow a remote authenticated attacker to modify device configuration data, resulting in denial-of-service (DoS) conditions on an affected device.
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Analysis
by VulDB Data Team • 10/04/2025
The vulnerability identified as CVE-2023-22913 represents a critical post-authentication command injection flaw within the Zyxel USG FLEX series and VPN series network security appliances. This weakness resides in the account_operator.cgi CGI program component of affected firmware versions, specifically targeting devices running firmware versions 4.50 through 5.35 for USG FLEX series and 4.30 through 5.35 for VPN series. The vulnerability classification aligns with CWE-77 and CWE-94, which respectively address command injection and code injection flaws that enable attackers to execute arbitrary commands on affected systems. The issue manifests as a post-authentication vector, meaning that an attacker must first establish valid credentials to exploit the vulnerability, though this requirement does not significantly diminish the threat level given the potential for privilege escalation and system compromise.
The technical implementation of this vulnerability stems from insufficient input validation and sanitization within the account_operator.cgi program, which processes user-supplied parameters without adequate filtering mechanisms. When authenticated users submit specific inputs to this CGI interface, the system fails to properly sanitize these parameters before incorporating them into system commands or configuration modifications. This flaw allows attackers to inject malicious commands that are then executed with the privileges of the authenticated user, potentially escalating to administrative level access depending on the user's permissions. The vulnerability specifically impacts configuration data modification capabilities, enabling attackers to manipulate device settings in ways that can disrupt normal operations and potentially cause complete system failure.
The operational impact of CVE-2023-22913 extends beyond simple denial-of-service conditions to encompass broader network security implications. While the primary consequence is the potential for denial-of-service scenarios that can render network appliances inoperative, the vulnerability's command injection nature opens pathways for more sophisticated attacks including persistent backdoor establishment, data exfiltration, and network reconnaissance. The affected devices operate as critical network infrastructure components, serving as firewalls and security gateways that protect enterprise networks from external threats. When compromised, these appliances can lose their protective capabilities, potentially allowing attackers to bypass security controls and gain unauthorized access to internal network segments. The vulnerability's presence in firmware versions spanning multiple releases indicates a prolonged exposure window that increases the likelihood of exploitation across various network deployments.
Mitigation strategies for this vulnerability should prioritize immediate firmware updates from Zyxel to address the identified command injection flaw. Organizations should implement strict access controls and network segmentation to limit the potential impact of compromised accounts, while also establishing robust monitoring procedures to detect anomalous configuration changes or unauthorized access attempts. The vulnerability's classification under the ATT&CK framework places it within the privilege escalation and persistence domains, suggesting that defenders should monitor for suspicious command execution patterns and unauthorized configuration modifications. Network administrators should also consider implementing additional security controls such as intrusion detection systems and privileged access management solutions to provide defense-in-depth against exploitation attempts. The remediation process requires careful planning due to the critical nature of these network security appliances, with downtime considerations and rollback procedures being essential components of any comprehensive mitigation strategy.