CVE-2026-76650 in TL-WR841N
Summary
by MITRE • 08/29/2026
A NULL pointer dereference vulnerability exists in TL-WR841N v14 in the UPnP service when processing SOAP state variable query requests. A specially crafted SOAP query may trigger unexpected termination or instability of the process hosting the UPnP service.
Successful exploitation may result in a denial-of-service condition affecting UPnP discovery, state query, or related management functionality until the affected process is restarted or the device is rebooted.
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Analysis
by VulDB Data Team • 08/29/2026
The vulnerability identified in TP-Link TL-WR841N v14 routers stems from an improper handling of NULL pointers within the Universal Plug and Play service implementation. Specifically, when the system processes SOAP state variable query requests, it fails to adequately validate input data before attempting to dereference a pointer that may be null. This flaw is characteristic of CWE-476, which describes a situation where code attempts to use a NULL pointer without first checking if the pointer is valid. In embedded systems like this router, such errors often arise from insufficient bounds checking or missing error handling routines during the parsing and processing of incoming network packets. The UPnP service, responsible for device discovery and configuration management on local networks, relies heavily on SOAP-based communication to maintain state information about connected devices and services. When a specially crafted request is sent that triggers this NULL pointer dereference, the underlying C code executes an invalid memory access operation.
From a technical perspective, the immediate consequence of this memory violation is typically a segmentation fault or similar critical error within the user-space process hosting the UPnP service. Because embedded devices often run services with limited isolation mechanisms compared to modern operating systems, such crashes can lead to unexpected termination of the specific daemon responsible for handling these requests. This results in an instability that disrupts normal operations. The attacker does not need authentication or prior access privileges beyond network reachability on the local area network segment where UPnP is enabled and listening. By sending a single malformed SOAP query packet, an adversary can exploit this weakness to crash the service process.
The operational impact of exploiting this vulnerability is primarily a denial-of-service condition targeting the UPnP functionality of the router. Once the process crashes or becomes unstable, devices on the network may fail to discover new services, existing state queries will return errors, and related management functionalities dependent on the UPnP daemon will cease to operate correctly. This disruption persists until the affected service is manually restarted by an administrator or the entire device undergoes a reboot cycle. While this vulnerability does not directly allow for remote code execution or privilege escalation in its current form, it significantly degrades network reliability and availability. For users relying on automatic port forwarding or device discovery features provided by UPnP, this crash effectively breaks those capabilities until remediation occurs.
Mitigation strategies should focus on both immediate operational fixes and long-term security hardening. The most effective solution is to apply the firmware update released by TP-Link that addresses this NULL pointer dereference issue through proper input validation and error handling in the SOAP processing logic. In environments where UPnP is not strictly required, disabling the service entirely eliminates the attack surface associated with this vulnerability. If UPnP must remain enabled for specific applications, administrators should consider restricting access to trusted IP ranges using firewall rules or VLAN segmentation to prevent unauthorized hosts from sending crafted requests. Additionally, monitoring logs for repeated crashes of the UPnP daemon can help in early detection and response to potential exploitation attempts. Adhering to industry standards such as CWE-476 during development and testing phases would have prevented this class of vulnerability, ensuring that all pointer dereferences are guarded by appropriate null checks before execution.