CVE-2026-42019 in Totolink
Summary
by MITRE • 10/21/2026
Multiple stack-based buffer overflow vulnerabilities exist in the boa formIpv6Setup pppoe functionality of Totolink X2000R 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 pppoe_dns1 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 Totolink X2000R routers running firmware version TOTOLINK-X2000R-Gh-V1.0.0-B20250421.1327, specifically affecting the formIpv6Setup function associated with Point-to-Point Protocol over Ethernet (PPPoE) configuration handling. This vulnerability is classified as a stack-based buffer overflow, which occurs when the application writes more data to a fixed-length block of memory on the call stack than it can hold. In this specific instance, the flaw is triggered by the pppoe_dns1 parameter, indicating that the input validation and bounds checking mechanisms for DNS server address entries are insufficient or entirely absent during the processing of HTTP requests destined for IPv6 setup configurations.
The technical mechanism behind this exploitation involves an attacker sending a specially crafted HTTP request containing a payload with excessive characters in the pppoe_dns1 field. Because the underlying C code does not properly verify the length of the input string before copying it into a stack-allocated buffer, the excess data overwrites adjacent memory locations on the stack. This overwrite can corrupt critical control flow data such as the return address or saved frame pointer. By carefully crafting the overflow payload to include shellcode and precise memory addresses, an attacker can hijack the execution flow of the router's firmware, leading to arbitrary code execution with the privileges of the compromised process, which is typically root level in embedded Linux environments.
From a threat modeling perspective, this vulnerability aligns with CWE-121: Stack-based Buffer Overflow, highlighting the failure to enforce proper bounds on memory operations within local stack variables. Furthermore, because exploitation requires an authenticated HTTP request, it falls under the category of vulnerabilities that require prior access or credential compromise, often categorized in MITRE ATT&CK frameworks under techniques involving Local Application Exploitation or potentially Command and Control if used for persistence after initial access. The requirement for authentication suggests that this is not a remote unauthenticated exploit but rather an insider threat vector or a consequence of compromised administrative credentials being leveraged to escalate privileges further within the device's internal network services.
The operational impact of successfully exploiting this vulnerability is severe, as it allows an attacker to gain full control over the router firmware. This can lead to complete compromise of the local area network, enabling traffic interception, man-in-the-middle attacks against connected devices, and using the compromised router as a pivot point for lateral movement into more sensitive internal systems. Additionally, persistent backdoors could be installed, allowing long-term unauthorized access even after reboots if the firmware image is modified or malicious scripts are injected via the web interface.
Mitigation strategies should prioritize immediate patching to the latest available firmware version from Totolink that addresses this buffer overflow issue in the formIpv6Setup function. If updating is not immediately feasible, network segmentation policies should be enforced to restrict access to the router's administrative HTTP interface solely to trusted management VLANs or IP ranges. Input validation controls must also be implemented at any proxy or gateway layer if possible, filtering out excessively long strings for DNS parameters before they reach the device. Long-term remediation involves adopting secure coding practices that enforce strict bounds checking and using static analysis tools during firmware development to detect stack-based buffer overflows prior to deployment.