CVE-2024-20339 in Firepower Threat Defense Software
Summary
by MITRE • 10/23/2024
A vulnerability in the TLS processing feature of Cisco Firepower Threat Defense (FTD) Software for Cisco Firepower 2100 Series could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.
This vulnerability is due to an issue that occurs when TLS traffic is processed. An attacker could exploit this vulnerability by sending certain TLS traffic over IPv4 through an affected device. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition and impacting traffic to and through the affected device.
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Analysis
by VulDB Data Team • 08/08/2025
The vulnerability identified as CVE-2024-20339 resides within the TLS processing capabilities of Cisco Firepower Threat Defense software operating on Cisco Firepower 2100 Series appliances. This represents a critical weakness that fundamentally undermines the availability of network security infrastructure by enabling unauthorized remote actors to disrupt service operations. The affected devices operate as network security appliances designed to protect enterprise environments from various cyber threats while maintaining uninterrupted network traffic flow, making this vulnerability particularly concerning for organizations relying on these systems for their security posture.
The technical flaw manifests specifically during the processing of Transport Layer Security traffic, where the software fails to properly handle certain TLS protocol interactions. This issue occurs when attackers transmit carefully crafted TLS traffic over IPv4 networks toward affected FTD devices, exploiting a weakness in the software's TLS handling mechanisms. The vulnerability stems from inadequate input validation and error handling within the TLS processing module, which fails to properly validate or sanitize incoming TLS packets before attempting to process them. According to CWE classification, this vulnerability aligns with CWE-20: Improper Input Validation, as the system does not adequately validate the TLS traffic it receives, and potentially with CWE-682: Incorrect Calculation, if the issue involves improper handling of cryptographic parameters or session management during TLS negotiations.
The operational impact of this vulnerability extends beyond simple service disruption to encompass complete network availability compromise. When successfully exploited, the vulnerability forces the affected Cisco Firepower device to undergo an automatic system reload, effectively taking the appliance offline and rendering it incapable of processing network traffic for the duration of the restart cycle. This DoS condition creates a cascading effect throughout the network infrastructure, as traffic that would normally be inspected and filtered by the FTD appliance is no longer protected, potentially exposing the network to other threats during the outage period. The vulnerability affects the fundamental operational continuity of security infrastructure, as organizations may experience extended periods of reduced network security coverage while the device recovers from the reload.
Organizations should implement immediate mitigations including applying the latest security patches from Cisco, which address the underlying TLS processing flaw through enhanced input validation and improved error handling mechanisms. Network segmentation strategies should be employed to limit exposure of affected devices to untrusted networks, while monitoring solutions should be configured to detect anomalous TLS traffic patterns that may indicate exploitation attempts. Additionally, implementing rate limiting on TLS connections and configuring the devices to disable unnecessary TLS processing capabilities can help reduce the attack surface. From an ATT&CK framework perspective, this vulnerability maps to T1499.004: Endpoint Denial of Service, as it specifically targets the availability of network security endpoints. The mitigation strategies should align with defensive techniques such as T1562.001: Impairing Defenses and T1595.001: Network Denial of Service, focusing on maintaining system availability and preventing exploitation through proper configuration and patch management practices.