CVE-2025-11676 in TL-WR940N V6
Summary
by MITRE • 11/20/2025
Improper input validation vulnerability in TP-Link System Inc. TL-WR940N V6 (UPnP modules), which allows unauthenticated adjacent attackers to perform DoS attack. This issue affects TL-WR940N V6 <= Build 220801.
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Analysis
by VulDB Data Team • 11/23/2025
The vulnerability identified as CVE-2025-11676 represents a critical improper input validation flaw within the UPnP modules of TP-Link TL-WR940N V6 wireless routers. This weakness specifically impacts devices running firmware versions up to and including Build 220801, creating a significant security risk for network administrators and end users who rely on these networking devices for their connectivity needs. The vulnerability's classification aligns with CWE-20, which addresses improper input validation as a fundamental software security weakness that can lead to various attack vectors including denial of service conditions.
The technical flaw manifests in the router's UPnP implementation where insufficient validation occurs on incoming network requests that are processed by the Universal Plug and Play service. This service, designed to allow automatic port configuration and device discovery within home and small office networks, becomes a vector for exploitation when malformed or excessively large input data is sent to the vulnerable device. Adjacent attackers who have network access to the router can leverage this weakness by crafting specific packets that trigger buffer overflow conditions or resource exhaustion within the UPnP module. The vulnerability's impact is particularly concerning as it requires no authentication credentials to exploit, making it accessible to any attacker within the router's network range.
The operational impact of this vulnerability extends beyond simple disruption as it enables unauthenticated denial of service attacks that can render the affected router completely non-functional. When exploited successfully, the vulnerability causes the UPnP service to crash or consume excessive system resources, resulting in complete network connectivity loss for all devices connected to the router. This condition affects the router's ability to perform its primary function of routing network traffic, potentially causing extended outages that can last until manual intervention or device reboot occurs. Network administrators may experience significant operational disruption when multiple devices in a network are affected, particularly in environments where the router serves as a critical infrastructure component.
Mitigation strategies for CVE-2025-11676 should prioritize immediate firmware updates from TP-Link to address the identified input validation issues within the UPnP modules. Organizations should implement network segmentation to isolate critical systems from potentially compromised devices, while also considering disabling UPnP functionality entirely if it is not required for network operations. Network monitoring solutions should be deployed to detect anomalous traffic patterns that may indicate exploitation attempts, and security teams should maintain awareness of the specific attack vectors that could be leveraged through the UPnP service. The ATT&CK framework categorizes this vulnerability under T1499.004 for network denial of service attacks, while the CWE classification of 20 emphasizes the need for comprehensive input validation controls. Additional defensive measures include implementing firewall rules to restrict UPnP traffic to trusted sources, conducting regular vulnerability assessments of network infrastructure, and maintaining updated security patches across all network devices to prevent similar exploitation vectors from being available to attackers.