CVE-2023-6906 in A7100RU
Summary
by MITRE • 12/18/2023
A vulnerability, which was classified as critical, was found in Totolink A7100RU 7.4cu.2313_B20191024. Affected is the function main of the file /cgi-bin/cstecgi.cgi?action=login of the component HTTP POST Request Handler. The manipulation of the argument flag with the input ie8 leads to buffer overflow. It is possible to launch the attack remotely. The exploit has been disclosed to the public and may be used. The identifier of this vulnerability is VDB-248268. NOTE: The vendor was contacted early about this disclosure but did not respond in any way.
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Analysis
by VulDB Data Team • 01/12/2024
The vulnerability identified as CVE-2023-6906 represents a critical buffer overflow flaw within the Totolink A7100RU wireless router firmware version 7.4cu.2313_B20191024. This vulnerability exists within the HTTP POST Request Handler component, specifically in the main function of the /cgi-bin/cstecgi.cgi script where the action parameter is set to login. The flaw manifests when processing the flag argument through user-supplied input containing the string "ie8", which triggers a buffer overflow condition that can be exploited remotely without requiring authentication. The vulnerability's classification as critical stems from its remote exploitability and the potential for arbitrary code execution within the router's operating system environment.
The technical implementation of this buffer overflow vulnerability occurs within the HTTP POST request handling mechanism of the router's web interface. When an attacker submits a malicious POST request containing the specific payload "ie8" in the flag parameter, the application fails to properly validate the input length before copying it into a fixed-size buffer. This improper bounds checking creates an exploitable condition where the overflow can overwrite adjacent memory locations including return addresses and control data structures. The vulnerability directly maps to CWE-121, which describes stack-based buffer overflow conditions, and potentially CWE-787, which covers out-of-bounds writes in heap-based buffers. The attack vector operates entirely through the web interface, making it accessible to remote adversaries without physical access to the device.
The operational impact of this vulnerability extends beyond simple remote code execution to encompass complete system compromise of the affected router. Successful exploitation could enable attackers to gain unauthorized administrative access to the device, allowing them to modify network configurations, install malicious firmware, redirect traffic through command and control servers, or establish persistent backdoors. The vulnerability's public disclosure through VDB-248268 indicates that exploit code is readily available in the wild, increasing the likelihood of active exploitation. Network traffic passing through the compromised router could be intercepted, modified, or redirected, potentially affecting all devices connected to the network. Additionally, the router's role as a gateway device means that compromise could provide attackers with a strategic foothold for lateral movement within the network infrastructure.
Mitigation strategies for CVE-2023-6906 should prioritize immediate firmware updates from the vendor when available, though the lack of vendor response to earlier disclosure attempts suggests this may not be forthcoming. Network administrators should implement firewall rules to restrict access to the router's web interface from untrusted networks, particularly blocking external access to the /cgi-bin/cstecgi.cgi endpoint. The implementation of network monitoring solutions that can detect unusual traffic patterns or malformed HTTP requests may help identify exploitation attempts. Device hardening measures including disabling unnecessary services, changing default credentials, and implementing secure network segmentation can reduce the attack surface. From an ATT&CK framework perspective, this vulnerability aligns with techniques such as T1059.007 (Command and Scripting Interpreter: PowerShell) and T1071.001 (Application Layer Protocol: Web Protocols) as attackers may leverage the compromised router for command execution and web-based communication. Organizations should also consider implementing network access control measures to prevent unauthorized devices from connecting to the network and establish incident response procedures specifically addressing router compromise scenarios.