CVE-2023-39239 in RT-AX56U V2
Summary
by MITRE • 09/07/2023
It is identified a format string vulnerability in ASUS RT-AX56U V2’s General function API. This vulnerability is caused by lacking validation for a specific value within its apply.cgi module. An unauthenticated remote attacker can exploit this vulnerability without privilege to perform remote arbitrary code execution, arbitrary system operation or disrupt service.
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Analysis
by VulDB Data Team • 09/07/2023
The vulnerability identified as CVE-2023-39239 represents a critical format string vulnerability within the ASUS RT-AX56U V2 router's General function API implementation. This flaw exists specifically within the apply.cgi module where insufficient input validation allows malicious actors to manipulate format specifiers in user-controlled data. The vulnerability stems from the router's web interface failing to properly sanitize or validate parameters passed to format string functions, creating an exploitable condition that can be leveraged by unauthenticated remote attackers. The affected device operates under the assumption that all incoming data from the network is trustworthy, which creates a dangerous attack surface where malicious input can be directly processed through vulnerable printf-style functions without proper sanitization.
The technical exploitation of this vulnerability enables attackers to achieve arbitrary code execution capabilities on the affected router system. When an attacker submits maliciously crafted input containing format specifiers to the vulnerable apply.cgi endpoint, the router's processing logic interprets these specifiers as instructions for memory access and data formatting rather than simple text input. This misinterpretation allows attackers to read arbitrary memory locations, potentially leading to information disclosure of sensitive system data including credentials, configuration parameters, or even kernel memory contents. The vulnerability's classification aligns with CWE-134 which specifically addresses the use of user-controlled format strings in applications, making this a well-documented and dangerous class of vulnerability that has been exploited in numerous other router and network device attacks.
The operational impact of this vulnerability extends beyond simple remote code execution to include complete system compromise and service disruption capabilities. An unauthenticated attacker can leverage this vulnerability to perform arbitrary system operations including but not limited to modifying router configuration settings, accessing restricted system files, disabling security features, or even installing malicious firmware. The service disruption aspect means that attackers could potentially render the router inoperable through carefully crafted input that causes the system to crash or enter an unstable state. This vulnerability particularly affects enterprise and home network environments where ASUS RT-AX56U V2 routers are deployed, as these devices typically serve as the primary gateway for network traffic and security enforcement.
Mitigation strategies for CVE-2023-39239 should prioritize immediate firmware updates from ASUS, as the vendor has likely released patches addressing this specific vulnerability. Network administrators should implement strict firewall rules to restrict access to the router's web interface from untrusted networks, particularly blocking direct access to the apply.cgi endpoint. The implementation of network monitoring solutions can help detect anomalous patterns in router API calls that might indicate exploitation attempts. Additionally, organizations should consider disabling unnecessary web management interfaces and implementing multi-factor authentication where possible. Security teams should also conduct thorough network segmentation to limit the potential impact of a successful exploitation, ensuring that even if one device is compromised, lateral movement within the network is restricted. The vulnerability's presence in a consumer-grade router highlights the importance of regular firmware updates and security assessments for all network infrastructure components, as these devices often remain unpatched for extended periods, creating persistent attack vectors for threat actors.