CVE-2021-1504 in ASA
Summary
by MITRE • 04/30/2021
Multiple vulnerabilities in Cisco Adaptive Security Appliance (ASA) Software and Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. These vulnerabilities are due to lack of proper input validation of the HTTPS request. An attacker could exploit these vulnerabilities by sending a crafted HTTPS request to an affected device. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition. Note: This vulnerability affects only specific AnyConnect and WebVPN configurations. For more information, see the Vulnerable Products section.
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Analysis
by VulDB Data Team • 07/28/2023
The vulnerability identified as CVE-2021-1504 represents a critical denial of service weakness affecting Cisco Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) software implementations. This vulnerability stems from insufficient input validation mechanisms within the HTTPS request processing pipeline of affected Cisco security appliances. The flaw specifically manifests when the system fails to properly validate incoming HTTPS requests, creating an exploitable condition that can be leveraged by remote attackers without requiring authentication credentials. Security researchers have identified that this vulnerability impacts only specific configurations involving AnyConnect and WebVPN services, making the attack surface more targeted but no less dangerous for affected organizations.
The technical exploitation of CVE-2021-1504 occurs through the submission of carefully crafted HTTPS requests that trigger improper input handling within the affected software components. When these malformed requests are processed by the vulnerable appliance, the system's insufficient validation mechanisms fail to properly sanitize or reject the malicious input. This processing failure results in an abnormal termination state where the affected device undergoes an automatic reload operation, effectively disrupting network security services and rendering the appliance temporarily unavailable to legitimate users. The vulnerability operates at the application layer of the network stack, specifically targeting the web-based management and authentication interfaces that rely on HTTPS protocols for secure communication.
From an operational impact perspective, CVE-2021-1504 presents a significant risk to enterprise network security infrastructure as it can be exploited remotely without authentication, making it particularly dangerous for organizations that maintain exposed web interfaces. The resulting denial of service condition can severely impact network availability and business continuity, especially when the affected appliance serves as a critical security gateway or acts as a primary authentication point for remote access services. Organizations utilizing AnyConnect and WebVPN configurations are particularly vulnerable since these services often provide essential remote access capabilities that may be targeted by threat actors seeking to disrupt business operations. The vulnerability's remote exploitability means that attackers can potentially target these devices from anywhere on the internet, amplifying the risk to organizations with exposed management interfaces.
Mitigation strategies for CVE-2021-1504 should prioritize immediate implementation of Cisco's official security advisories and software updates that address the input validation deficiencies in affected software versions. Organizations should also consider implementing network segmentation measures to limit exposure of vulnerable appliances to untrusted networks, while monitoring for suspicious HTTPS traffic patterns that may indicate exploitation attempts. Network administrators should verify their current software versions against Cisco's vulnerability databases and apply patches as soon as possible to remediate the issue. Additionally, implementing intrusion detection systems with signature-based detection capabilities can help identify and block exploitation attempts targeting this specific vulnerability. The weakness aligns with CWE-20, which describes improper input validation as a fundamental security flaw that can lead to various security consequences including denial of service conditions, making it essential for organizations to maintain robust input validation controls throughout their network infrastructure.