CVE-2026-42026 in Totolink
Summary
by MITRE • 10/21/2026
Multiple exploitable stack-based buffer overflow vulnerabilities exist in the boa formIpv6Setup dhcp_dns functionality of X2000R (version(s): TOTOLINK-X2000R-Gh-V1.0.0-B20250421.1327). A specially crafted HTTP request can lead to arbitrary code execution. An attacker can make an authenticated HTTP request to trigger these vulnerabilities. This vulnerability concerns the dhcp_dns2 parameter.
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Analysis
by VulDB Data Team • 10/21/2026
The identified security flaw resides within the embedded web server component of the TOTOLINK X2000R router, specifically affecting firmware version 1.0.0-B20250421.1327 and potentially earlier iterations that share the same codebase. The vulnerability is located in the formIpv6Setup function, which handles the configuration parameters for IPv6 settings via a web-based management interface. This component processes user-supplied input to configure network interfaces, including DNS server addresses and DHCP client settings. The specific point of failure involves the handling of the dhcp_dns2 parameter, where the application fails to adequately validate or bound-check the length of the incoming string data before copying it into a fixed-size stack buffer.
This architectural deficiency constitutes a classic stack-based buffer overflow condition, categorized under CWE-120: Buffer Copy without Checking Size of Input. When an attacker submits a specially crafted HTTP request containing a payload that exceeds the allocated memory space for the dhcp_dns2 variable, the excess data overwrites adjacent memory locations on the call stack. This overwrite can corrupt critical control flow data such as return addresses or function pointers stored in the stack frame. Because the vulnerable code executes with elevated privileges typical of embedded device management interfaces, successfully exploiting this overflow allows an attacker to redirect program execution to arbitrary shellcode injected into the buffer itself or elsewhere in memory.
The operational impact of this vulnerability is severe, resulting in remote unauthenticated-like access if authentication requirements are bypassed or weak credentials exist, though the description notes that authenticated HTTP requests are required to trigger it. This implies a lower attack complexity compared to fully unauthenticated exploits but still poses a critical risk to network integrity. Successful exploitation leads to arbitrary code execution on the router's processor, which typically runs Linux-based embedded systems with limited security mitigations such as Address Space Layout Randomization or non-executable stack protections. Consequently, an attacker can gain full control over the device, enabling them to pivot into the internal local area network, intercept traffic, modify routing tables, install persistent malware, or use the compromised router as a botnet node for distributed denial-of-service attacks.
From a threat intelligence perspective, this vulnerability aligns with MITRE ATT&CK techniques related to initial access and execution on embedded devices. The exploitation vector involves crafting malicious HTTP requests that target specific CGI endpoints, which is consistent with common attack patterns observed in IoT malware families targeting home routers. The reliance on authenticated access suggests that attackers may need to first compromise user credentials through phishing, brute force, or credential stuffing before leveraging this buffer overflow for privilege escalation and code execution.
Mitigation strategies should prioritize immediate firmware updates provided by the vendor if available, as patching typically involves implementing strict input validation functions such as strncpy with explicit length limits instead of unsafe string copy operations like strcpy. Network administrators who cannot immediately update their firmware should restrict access to the router's management interface by disabling remote administration features and ensuring that administrative ports are not exposed to untrusted networks. Additionally, enforcing strong, unique passwords for all user accounts reduces the likelihood of an attacker obtaining the necessary authentication credentials to trigger this vulnerability. Long-term remediation requires vendors to adopt secure coding practices, including static analysis tools during development and regular security audits focused on memory safety in embedded C codebases.