CVE-2023-33011 in ATP
Summary
by MITRE • 07/17/2023
A format string vulnerability in the Zyxel ATP series firmware versions 5.10 through 5.36 Patch 2, USG FLEX series firmware versions 5.00 through 5.36 Patch 2, USG FLEX 50(W) series firmware versions 5.10 through 5.36 Patch 2, USG20(W)-VPN series firmware versions 5.10 through 5.36 Patch 2, and VPN series firmware versions 5.00 through 5.36 Patch 2, could allow an unauthenticated, LAN-based attacker to execute some OS commands by using a crafted PPPoE configuration on an affected device when the cloud management mode is enabled.
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Analysis
by VulDB Data Team • 07/18/2023
The vulnerability identified as CVE-2023-33011 represents a critical format string flaw within multiple Zyxel network security device series including ATP, USG FLEX, USG FLEX 50(W), USG20(W)-VPN, and VPN series devices. This vulnerability exists in firmware versions ranging from 5.10 through 5.36 Patch 2 across affected models, creating a significant security risk for organizations relying on these network appliances. The flaw manifests specifically when the cloud management mode is enabled on affected devices, making it particularly concerning for enterprises that utilize remote management capabilities. The vulnerability is classified under CWE-134 which specifically addresses format string vulnerabilities, where improper use of format specifiers in functions like printf can lead to arbitrary code execution. This weakness allows attackers to manipulate the format string parameters and potentially overwrite memory locations, leading to unauthorized command execution on the underlying operating system.
The technical exploitation of this vulnerability requires an unauthenticated attacker to be positioned on the local area network of the affected device, which significantly reduces the attack surface compared to remotely exploitable vulnerabilities. However, the impact remains severe as attackers can leverage the crafted PPPoE configuration to trigger the format string vulnerability. When the cloud management mode is active, the device's configuration processing becomes more complex and potentially vulnerable to manipulation. The attack vector specifically targets the device's handling of PPPoE (Point-to-Point Protocol over Ethernet) configuration parameters, where the format string vulnerability is triggered during the parsing of malformed input data. This type of attack aligns with ATT&CK technique T1059.001 for command and script interpreter execution, as successful exploitation would enable attackers to execute arbitrary operating system commands. The vulnerability essentially allows for privilege escalation from a local network user to full system control, bypassing traditional authentication mechanisms that would normally be required for administrative access.
The operational impact of this vulnerability extends beyond simple command execution, as it provides attackers with persistent access to network infrastructure that could be used for further lateral movement within the organization. Organizations utilizing Zyxel devices in their network security infrastructure face potential exposure to advanced persistent threats that could compromise network integrity, data confidentiality, and availability. The vulnerability's presence in multiple device series indicates a systemic issue within Zyxel's firmware development processes, particularly in input validation and string handling routines. Network administrators may not immediately detect exploitation attempts as the malicious activity could appear as legitimate system behavior, especially when cloud management is enabled and normal operational traffic is present. The attack's reliance on cloud management mode creates a unique risk profile where even organizations with proper network segmentation may be vulnerable if they maintain cloud connectivity for device management purposes. This vulnerability demonstrates the critical importance of firmware security updates and proper network segmentation in protecting against sophisticated attacks that exploit seemingly minor implementation flaws.
Organizations should prioritize immediate firmware updates from Zyxel to address this vulnerability, as the manufacturer has likely released patches to resolve the format string handling issues. Network segmentation strategies should be implemented to isolate devices that support cloud management features from critical network segments, reducing the potential attack surface. Monitoring for unusual PPPoE configuration changes and anomalous network behavior should be enabled to detect potential exploitation attempts. Security teams should conduct comprehensive vulnerability assessments of all affected Zyxel device models within their network infrastructure, particularly focusing on devices operating in cloud management mode. The vulnerability also highlights the need for regular security testing of network infrastructure components, including third-party firmware validation and runtime monitoring. Organizations should consider implementing network access controls to prevent unauthorized LAN access to critical network devices, as the attack requires local network presence. Incident response procedures should be updated to include detection and response protocols for format string vulnerabilities, ensuring that security teams are prepared to handle exploitation attempts that could lead to complete system compromise. The vulnerability serves as a reminder of the critical importance of secure coding practices in embedded systems and the potential for seemingly minor flaws to create significant security risks in network infrastructure devices.