CVE-2018-17020 in GT-AC5300
Summary
by MITRE
ASUS GT-AC5300 devices with firmware through 3.0.0.4.384_32738 allow remote attackers to cause a denial of service via a single "GET / HTTP/1.1\r\n" line.
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Analysis
by VulDB Data Team • 03/23/2020
The vulnerability identified as CVE-2018-17020 affects ASUS GT-AC5300 wireless routers running firmware versions up to 3.0.0.4.384_32738. This represents a denial of service condition that can be triggered through a simple HTTP request containing only a single GET line without proper HTTP headers or formatting. The flaw exists in the web server component of the router's firmware, specifically in how it processes incoming HTTP requests. Attackers can exploit this vulnerability by sending a malformed HTTP request that consists solely of the GET method followed by a single line feed character, without proper HTTP version specification or additional headers that would normally be required for a valid HTTP request. This particular attack vector demonstrates a failure in input validation and request parsing within the router's embedded web server implementation.
The technical nature of this vulnerability stems from inadequate validation of HTTP request syntax in the router's web interface. When the web server receives the malformed request containing only a single GET line, it fails to properly handle this malformed input, leading to a system crash or restart that results in denial of service for legitimate users. The vulnerability is classified under CWE-129 as an insufficient input validation issue, specifically manifesting as a failure to properly validate HTTP request format. This type of vulnerability represents a classic example of a buffer overflow or parsing error that occurs when the system does not adequately check the structure of incoming data before processing it. The attack requires minimal sophistication and can be executed remotely, making it particularly dangerous as it allows an unauthenticated attacker to disrupt network services without requiring any special privileges or credentials.
The operational impact of this vulnerability extends beyond simple service disruption as it can affect network availability for all users connected to the affected router. When exploited successfully, the denial of service condition renders the router inaccessible, preventing users from accessing the web-based management interface, configuring network settings, or utilizing internet connectivity. Network administrators may experience significant downtime while investigating and resolving the issue, particularly if multiple devices are affected within the same network segment. The vulnerability also demonstrates a broader concern about embedded device security, as it shows that consumer-grade networking equipment often lacks robust input validation mechanisms that would be expected in enterprise-grade systems. This type of vulnerability can be particularly problematic in environments where network reliability is critical, as it allows attackers to disrupt services with minimal effort and resources.
Mitigation strategies for CVE-2018-17020 should focus on firmware updates provided by ASUS, which typically include enhanced input validation and proper HTTP request parsing mechanisms. Network administrators should implement regular firmware update schedules and maintain inventory of all network devices to ensure timely patch deployment. Additional defensive measures include network segmentation to isolate affected devices, implementing intrusion detection systems that can identify malformed HTTP requests, and configuring access controls to limit exposure of the router's web interface to trusted networks only. The vulnerability also highlights the importance of following security best practices such as those outlined in the NIST Cybersecurity Framework and ISO 27001 standards for embedded system security. Organizations should consider implementing network monitoring solutions that can detect unusual traffic patterns or malformed requests that may indicate exploitation attempts, as this vulnerability can be part of a broader attack campaign targeting network infrastructure devices. The ATT&CK framework categorizes this type of vulnerability under T1499.004 for Network Denial of Service, emphasizing the need for both preventive measures and incident response capabilities when dealing with such network infrastructure attacks.