CVE-2018-15700 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 Referer field.
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Analysis
by VulDB Data Team • 03/28/2020
The vulnerability identified as CVE-2018-15700 affects the web interface of TP-Link TL-WRN841N wireless router running firmware version 0.9.1 4.16 v0348.0. This device operates as a wireless router and access point, serving as a critical network infrastructure component that provides connectivity and security services to home and small office networks. The vulnerability manifests within the router's web management interface, which is accessible via HTTP protocol and typically used by network administrators to configure and monitor the device's settings. The affected firmware version represents a specific release that contains a software flaw in the HTTP request processing logic, making it susceptible to malicious input manipulation.
The technical flaw stems from inadequate input validation within the HTTP header processing mechanism of the router's web server component. When an unauthenticated user on the local area network sends an HTTP request containing a crafted Referer field, the device fails to properly sanitize or validate this input parameter. The web interface does not implement proper bounds checking or input sanitization routines for the Referer header, allowing maliciously constructed values to trigger unexpected behavior in the underlying HTTP processing stack. This particular vulnerability classifies under CWE-20 as "Improper Input Validation" since the system does not adequately validate the format and content of the Referer header field. The flaw specifically impacts the router's ability to process HTTP requests correctly, leading to system instability and potential service interruption.
The operational impact of this vulnerability is significant as it enables a remote denial of service attack that can be executed by any user within the local network segment without requiring authentication credentials. An attacker can simply craft a malicious HTTP request with an oversized or malformed Referer header value and send it to the router's web interface, causing the device to crash or become unresponsive. This renders the router's management interface inaccessible, preventing legitimate administrators from configuring or monitoring the device. The denial of service affects not only the administrative capabilities but also potentially disrupts network connectivity for all devices relying on the router's services. The attack vector is particularly concerning because it requires no authentication, making it accessible to anyone with network access, and the impact is immediate and severe, as demonstrated by the specific firmware version affected.
Mitigation strategies for this vulnerability should focus on both immediate remediation and long-term security hardening. The primary solution involves updating to a newer firmware version that contains proper input validation for HTTP headers, which should be obtained directly from TP-Link's official website. Network administrators should implement network segmentation to limit local network access to only trusted users and devices, reducing the attack surface. Additionally, implementing firewall rules to restrict access to the router's web interface from untrusted networks and monitoring for unusual HTTP request patterns can help detect potential exploitation attempts. The vulnerability demonstrates the importance of secure coding practices and input validation, aligning with ATT&CK technique T1499.004 for "Endpoint Denial of Service" and highlighting the need for proper HTTP header handling as outlined in security best practices for embedded systems. Organizations should also consider implementing network monitoring solutions that can detect abnormal traffic patterns indicating potential exploitation attempts.