CVE-2026-121597 in A950RG
Summary
by MITRE • 11/04/2026
A weakness has been identified in TOTOLINK A950RG 4.1.2cu.5268_B20221104. This affects the function setAppEasyWizardConfig of the file /cgi-bin/cstecgi.cgi of the component Easy Setup Wizard Handler. Executing a manipulation of the argument functionType can lead to stack-based buffer overflow. The attack may be performed from remote. The exploit has been made available to the public and could be used for attacks.
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Analysis
by VulDB Data Team • 11/04/2026
The vulnerability identified in TOTOLINK A950RG firmware version 4.1.2cu.5268_B20221104 represents a critical security flaw within the device's web management interface, specifically affecting the Easy Setup Wizard Handler component. This subsystem is responsible for processing configuration requests submitted by users or automated scripts to simplify network setup procedures. The core of the issue resides in the setAppEasyWizardConfig function located within the /cgi-bin/cstecgi.cgi script. As a Common Gateway Interface (CGI) application, this binary handles HTTP POST data directly from remote clients without adequate input validation or bounds checking on specific parameters. This architectural design choice creates an environment where malicious actors can interact with low-level memory operations through high-level network protocols, bypassing many traditional perimeter defenses that do not inspect payload content deeply enough to detect buffer manipulation attempts.
The technical nature of this flaw is a stack-based buffer overflow triggered by the functionType argument passed during execution of the setAppEasyWizardConfig routine. When an attacker sends a crafted HTTP request containing a functionType value with excessive length, the application fails to verify that the input fits within the allocated memory space on the call stack. Instead of truncating or rejecting the oversized data, the program copies it into a fixed-size buffer, causing adjacent memory locations to be overwritten. This corruption can overwrite critical control flow data such as return addresses and saved frame pointers stored on the stack. Because this vulnerability is exploitable remotely via standard web traffic, an attacker does not need physical access or prior authentication credentials if the management interface is exposed to untrusted networks or has weak default login settings often found in consumer-grade routers.
The operational impact of successfully exploiting this buffer overflow is severe and typically results in arbitrary code execution with the privileges of the CGI process, which frequently runs as root on embedded Linux devices like home routers. By carefully crafting the payload to overwrite the return address with a pointer to shellcode injected into the same request or via environment variables, an attacker can gain full control over the device. This level of compromise allows for significant network disruption and further exploitation within the local area network. Compromised IoT devices are frequently recruited into botnets such as Mirai variants to launch distributed denial-of-service attacks against other targets. Additionally, attackers may use the compromised router as a pivot point to scan internal networks, intercept unencrypted traffic through man-in-the-middle techniques, or install persistent backdoors for long-term espionage and data exfiltration from connected devices like computers and smartphones.
From a classification perspective, this vulnerability aligns with CWE-120 Buffer Copy without Checking Size of Input in C/C++ as the root cause, while the exploitation technique falls under ATT&CK Tactic TA0004 Privilege Escalation and specifically techniques such as T1068 Exploitation for Privilege Escalation. The remote nature of the attack also maps to ATT&CK tactic TA0001 Initial Access via valid accounts or service vulnerabilities, particularly when combined with default credential usage common in these devices. To mitigate this risk, users should immediately update their TOTOLINK A950RG firmware to a patched version that addresses the input validation logic within cstecgi.cgi if such an update is available from the vendor. In cases where updates are not provided or delayed, network segmentation strategies can limit exposure by placing IoT devices on isolated VLANs with restricted access to critical internal resources. Furthermore disabling remote management features and changing default administrative passwords reduces the attack surface significantly. Security monitoring tools should be configured to detect anomalous HTTP POST requests containing unusually large payloads directed at CGI endpoints as an indicator of potential exploitation attempts.