CVE-2020-3306 in ASA
Summary
by MITRE
A vulnerability in the DHCP module of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on the affected device. The vulnerability is due to incorrect processing of certain DHCP packets. An attacker could exploit this vulnerability by sending a crafted DHCP packet to the affected device. A successful exploit could allow the attacker to cause a DoS condition on the affected device.
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Analysis
by VulDB Data Team • 10/15/2020
The vulnerability identified as CVE-2020-3306 represents a critical denial of service weakness within Cisco's security infrastructure, specifically affecting the DHCP processing capabilities of Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) software implementations. This flaw resides in the fundamental packet handling mechanisms that govern how these security appliances process dynamic host configuration protocol communications, creating an exploitable condition that can be leveraged by remote attackers without requiring authentication credentials. The vulnerability stems from inadequate validation and processing of DHCP packets, which are standard network communications used to dynamically assign IP addresses and other network configuration parameters to devices on a network. When these malformed packets are received by the affected Cisco devices, the software fails to properly handle the unexpected packet structures, leading to system instability and potential complete service disruption.
The technical exploitation of this vulnerability occurs through the deliberate crafting of malformed DHCP packets that trigger memory corruption or resource exhaustion within the ASA or FTD software stack. Attackers can send specially constructed DHCP messages that contain invalid or unexpected field values, malformed option structures, or other aberrant packet characteristics that the vulnerable software cannot properly parse or discard. This improper handling leads to memory leaks, buffer overflows, or other internal state corruption conditions that ultimately result in the device becoming unresponsive or crashing entirely. The nature of this flaw aligns with CWE-129, which describes improper validation of input boundaries, and CWE-125, which addresses out-of-bounds read conditions. The vulnerability demonstrates characteristics consistent with the attack pattern described in the MITRE ATT&CK framework under the T1499.004 technique for network denial of service attacks, where adversaries target network infrastructure to disrupt services for legitimate users.
The operational impact of CVE-2020-3306 extends beyond simple service interruption to potentially compromise the entire network security posture of organizations relying on affected Cisco appliances. When a security device becomes unavailable due to this DoS condition, network traffic flows through the device are disrupted, potentially exposing network segments to unauthorized access or preventing legitimate administrative access to the security infrastructure itself. The attack vector is particularly concerning because it requires no authentication and can be executed from any network location capable of reaching the targeted device, making it a significant threat to network availability and business continuity. Organizations may experience extended downtime while attempting to restore services, and the vulnerability could be exploited repeatedly, causing persistent service degradation that impacts network performance and reliability. The vulnerability affects multiple Cisco product lines including ASA 5500 Series, ASA 5500-X Series, and Firepower Threat Defense appliances, with various software versions being susceptible to exploitation.
Mitigation strategies for this vulnerability require immediate implementation of security patches provided by Cisco, as well as network-level protective measures to reduce exposure. Organizations should prioritize applying the relevant security updates from Cisco's official advisory, which typically include code modifications that properly validate DHCP packet structures and implement robust error handling for malformed inputs. Network administrators should also consider implementing DHCP filtering rules at network boundaries to limit the types of DHCP packets that can reach the vulnerable devices, while deploying monitoring solutions to detect unusual DHCP traffic patterns that may indicate exploitation attempts. Additional defensive measures include implementing redundant security appliances to maintain network availability during patching operations, configuring logging and alerting mechanisms to detect DoS conditions, and establishing incident response procedures specifically for handling such vulnerabilities. The implementation of these mitigations should align with industry best practices outlined in the NIST Cybersecurity Framework and ISO 27001 standards for information security management, ensuring comprehensive protection against both current and potential future exploitation attempts.