CVE-2018-15388 in ASA
Summary
by MITRE
A vulnerability in the WebVPN login process of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause increased CPU utilization on an affected device. The vulnerability is due to excessive processing load for existing WebVPN login operations. An attacker could exploit this vulnerability by sending multiple WebVPN login requests to the device. A successful exploit could allow the attacker to increase CPU load on the device, resulting in a denial of service (DoS) condition.
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Analysis
by VulDB Data Team • 09/12/2023
The vulnerability identified as CVE-2018-15388 represents a significant denial of service weakness within Cisco's Adaptive Security Appliance and Firepower Threat Defense software platforms. This flaw specifically targets the WebVPN login process, which serves as a critical authentication mechanism for remote network access. The vulnerability manifests when the system encounters excessive processing demands during legitimate WebVPN authentication attempts, creating a scenario where normal operational traffic can be exploited to generate abnormal resource consumption patterns. The affected devices operate under the assumption that authentication requests will follow standard processing patterns, but the flaw allows for exploitation through carefully crafted multiple login attempts that overwhelm the system's processing capabilities.
Technical analysis reveals that the vulnerability stems from insufficient input validation and resource management within the WebVPN authentication module of Cisco's security appliances. The flaw operates by causing the system to perform excessive computational work during the login process without adequate rate limiting or resource allocation controls. When multiple WebVPN login requests are simultaneously processed, the system's CPU utilization increases dramatically beyond normal operational parameters. This occurs because the authentication routine does not properly handle concurrent or rapid successive authentication attempts, leading to a cascading effect where each additional request consumes progressively more system resources. The vulnerability is classified as a resource exhaustion issue that directly impacts the availability of the security appliance services, making it particularly dangerous in network environments where continuous availability is critical.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the overall security posture of affected networks. An unauthenticated remote attacker can leverage this weakness to launch denial of service attacks against Cisco ASA and FTD devices, effectively rendering them unable to process legitimate authentication requests or provide their intended security services. The attack vector requires no authentication credentials, making it particularly dangerous as it can be exploited from any location on the internet. The resulting CPU utilization spikes can cause the affected devices to become unresponsive, preventing legitimate users from accessing network resources while simultaneously creating opportunities for additional attacks. This vulnerability directly relates to CWE-400, which categorizes resource exhaustion as a fundamental weakness in software design that can lead to denial of service conditions.
Mitigation strategies for CVE-2018-15388 should focus on implementing rate limiting controls and monitoring mechanisms to detect abnormal authentication patterns. Network administrators should deploy configuration changes that limit the number of concurrent WebVPN login attempts and establish automated alerts for unusual CPU utilization patterns. Cisco recommends applying the latest software patches and updates that address the specific processing inefficiencies in the WebVPN authentication module. The implementation of access control lists and firewall rules can help limit the sources of WebVPN authentication requests, while monitoring systems should be configured to detect and respond to rapid successive login attempts. From an ATT&CK framework perspective, this vulnerability aligns with techniques related to denial of service and resource exhaustion, specifically targeting the availability aspect of the CIA triad. Organizations should also consider implementing redundant security appliances and failover mechanisms to maintain network availability during potential exploitation attempts. The vulnerability demonstrates the importance of proper input validation and resource management in security-critical applications, emphasizing that authentication mechanisms must be designed to withstand both legitimate and malicious usage patterns.