CVE-2018-15701 in TL-WRN841N
Summary
by MITRE
The web interface in TP-Link TL-WRN841N 0.9.1 4.16 v0348.0 is vulnerable to a denial of service when an unauthenticated LAN user sends a crafted HTTP header containing an unexpected Cookie field.
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Analysis
by VulDB Data Team • 03/28/2020
The TP-Link TL-WRN841N router model running firmware version 0.9.1 4.16 v0348.0 presents a significant denial of service vulnerability through its web interface implementation. This vulnerability specifically targets the HTTP header processing mechanism where the system fails to properly validate or sanitize incoming Cookie fields. The flaw exists in the web server component that handles HTTP requests from local network users who are not authenticated to the device. When an unauthenticated user on the local network sends a specially crafted HTTP request containing an unexpected Cookie field, the router's web interface becomes unstable and ceases to respond to legitimate requests.
The technical nature of this vulnerability stems from insufficient input validation within the router's HTTP processing stack. The web interface does not implement proper bounds checking or sanitization of Cookie header values, allowing maliciously formatted data to trigger unexpected behavior in the underlying web server implementation. This weakness represents a classic example of improper input validation that can lead to resource exhaustion or application crashes. The vulnerability is particularly concerning because it requires no authentication to exploit, making it accessible to any user on the local network segment. The attack vector specifically targets the Cookie field within HTTP headers, which is commonly used for session management and other web application functions.
The operational impact of this vulnerability extends beyond simple service disruption as it can render the entire router management interface inaccessible to authorized users. Network administrators who rely on the web interface for configuration and monitoring purposes would experience complete loss of access to the device's management functions until the router is manually restarted. This denial of service condition affects both local and potentially remote management capabilities, as the web interface is often the primary means of device administration. The vulnerability creates a persistent state where legitimate users cannot access the device's configuration interface, forcing administrators to physically reboot the device or wait for the system to recover automatically. This type of vulnerability can be particularly problematic in enterprise environments where router availability is critical for network operations and where unauthorized local network users could exploit this weakness to disrupt network services.
The vulnerability aligns with CWE-20, which describes improper input validation, and demonstrates characteristics consistent with attack patterns found in the MITRE ATT&CK framework under the initial access and privilege escalation domains. Network defenders should implement network segmentation to limit local network access to administrative devices and consider deploying network monitoring tools to detect unusual HTTP traffic patterns that might indicate exploitation attempts. The recommended mitigations include applying firmware updates from TP-Link when available, implementing network access controls to restrict local network access to administrative interfaces, and configuring network-based intrusion detection systems to monitor for suspicious HTTP header patterns. Additionally, organizations should consider disabling unnecessary web interface access and implementing alternative management protocols such as SSH or SNMP with proper authentication mechanisms to reduce the attack surface and provide more secure administrative access to network devices.