CVE-2020-3480 in IOS XE
Summary
by MITRE
Multiple vulnerabilities in the Zone-Based Firewall feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause the device to reload or stop forwarding traffic through the firewall. The vulnerabilities are due to incomplete handling of Layer 4 packets through the device. An attacker could exploit these vulnerabilities by sending a certain sequence of traffic patterns through the device. A successful exploit could allow the attacker to cause the device to reload or stop forwarding traffic through the firewall, resulting in a denial of service. For more information about these vulnerabilities, see the Details section of this advisory.
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Analysis
by VulDB Data Team • 09/25/2020
The vulnerability identified as CVE-2020-3480 resides within the Zone-Based Firewall implementation of Cisco IOS XE Software, representing a critical security flaw that affects network infrastructure devices. This issue specifically targets the handling of Layer 4 packet processing within the firewall's operational framework, creating potential pathways for unauthorized remote exploitation. The vulnerability stems from inadequate processing mechanisms that fail to properly manage certain traffic patterns, leading to system instability and service disruption. Network administrators and security professionals must understand that this flaw exists at the core of Cisco's firewall functionality, potentially compromising the integrity of network traffic control and device availability.
The technical exploitation of this vulnerability occurs through carefully crafted sequences of Layer 4 traffic that trigger incomplete packet handling routines within the Zone-Based Firewall module. When the affected Cisco IOS XE devices receive these specific traffic patterns, the system fails to properly process the packets and instead experiences either a complete device reload or a cessation of traffic forwarding capabilities through the firewall. This behavior manifests as a denial of service condition that can be triggered remotely without requiring authentication credentials, making it particularly dangerous for network environments where such devices serve as critical traffic gateways. The flaw demonstrates a clear weakness in the input validation and packet processing logic of the firewall's Layer 4 handling components.
Operational impact of CVE-2020-3480 extends beyond simple service disruption to potentially compromise network availability and traffic flow management across affected infrastructure. Organizations relying on Cisco IOS XE devices for firewall protection face significant risk of unauthorized denial of service attacks that could disrupt business operations and compromise network security posture. The remote exploitation capability means attackers can target these devices from outside the network perimeter, making the vulnerability particularly dangerous for publicly accessible network equipment. Network traffic monitoring systems may not immediately detect the subtle indicators of exploitation, as the device behavior can appear as normal network operation until the service disruption occurs, creating potential blind spots in security monitoring and incident response.
Mitigation strategies for CVE-2020-3480 should prioritize immediate software updates from Cisco, specifically addressing the Zone-Based Firewall implementation in IOS XE Software. Organizations must implement network segmentation and access controls to limit exposure of affected devices to untrusted networks while applying the relevant security patches. Network administrators should consider implementing traffic monitoring and anomaly detection systems to identify potential exploitation attempts through unusual packet patterns. Additionally, temporary workarounds such as disabling Zone-Based Firewall functionality or implementing strict access control lists may provide interim protection while permanent fixes are deployed. The vulnerability aligns with CWE-122 which addresses buffer overflow conditions in network protocol handling, and represents a potential ATT&CK technique involving denial of service through network infrastructure manipulation. Security teams should also consider implementing network access control measures to prevent unauthorized access to network devices and establish incident response procedures for rapid remediation of affected systems.