CVE-2024-20494 in ASA
Summary
by MITRE • 10/23/2024
A vulnerability in the TLS cryptography functionality of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial of service (DoS) condition.
This vulnerability is due to improper data validation during the TLS 1.3 handshake. An attacker could exploit this vulnerability by sending a crafted TLS 1.3 packet to an affected system through a TLS 1.3-enabled listening socket. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.
Note: This vulnerability can also impact the integrity of a device by causing VPN HostScan communication failures or file transfer failures when Cisco ASA Software is upgraded using Cisco Adaptive Security Device Manager (ASDM).
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Analysis
by VulDB Data Team • 08/01/2025
The vulnerability identified as CVE-2024-20494 represents a critical weakness in the cryptographic processing capabilities of Cisco's network security infrastructure, specifically affecting both Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software. This flaw manifests within the TLS 1.3 handshake implementation where inadequate input validation occurs during the cryptographic negotiation process, creating an exploitable condition that can be leveraged by remote attackers without requiring authentication credentials. The vulnerability's impact extends beyond simple service disruption as it fundamentally compromises the reliability and integrity of security communications within affected network environments. The improper data validation mechanism fails to properly sanitize or verify the integrity of incoming TLS 1.3 handshake packets, creating a pathway for malicious actors to manipulate the cryptographic session establishment process.
The technical exploitation of this vulnerability occurs through the manipulation of TLS 1.3 protocol packets sent to listening sockets that have TLS 1.3 enabled, with the attack vector being particularly concerning due to its remote nature and lack of authentication requirements. When a crafted TLS 1.3 packet is received and processed by the vulnerable software, the insufficient validation leads to an unexpected system state that triggers an automatic device reload or reboot sequence. This behavior constitutes a denial of service condition that can be repeatedly triggered, potentially leading to sustained network disruption and service unavailability. The flaw specifically targets the handshake phase of TLS 1.3, which is critical for establishing secure communication channels, making it particularly dangerous for network security devices that rely heavily on proper TLS implementation for their operations. This vulnerability aligns with CWE-20, which describes improper input validation, and represents a classic example of how cryptographic protocol implementation flaws can create system instability.
The operational impact of CVE-2024-20494 extends significantly beyond immediate denial of service conditions, as the vulnerability can compromise the integrity of critical security functions within affected devices. Network administrators face the potential for unexpected device reboots that can interrupt ongoing security operations, particularly affecting VPN connectivity and HostScan communications that are essential for remote access security policies. The vulnerability's influence on file transfer operations during software upgrades through Cisco Adaptive Security Device Manager (ASDM) creates additional operational concerns, as it can cause upgrade failures and potentially leave devices in inconsistent states. This disruption can severely impact security posture maintenance and network management processes, as administrators may be unable to perform critical updates or maintenance activities during active attacks. The vulnerability's potential to cause repeated device reloads also creates a risk of accelerated hardware degradation and increased administrative overhead, as system monitoring and recovery procedures must be continuously managed. From an ATT&CK framework perspective, this vulnerability maps to T1499.004 (Endpoint Denial of Service) and T1566.001 (Phishing via Service) as it can be leveraged to disrupt network services and potentially used in broader attack campaigns targeting network infrastructure.
Mitigation strategies for CVE-2024-20494 should prioritize immediate implementation of vendor-provided security patches and updates, as these will contain the necessary fixes for the TLS 1.3 handshake validation logic. Network administrators should consider implementing temporary network segmentation or access controls to limit exposure while patches are deployed, particularly focusing on restricting access to TLS 1.3 enabled services from untrusted networks. The vulnerability's nature suggests that monitoring for unusual device restart patterns or unexpected TLS handshake activity could serve as an early detection mechanism, though such monitoring should not replace proper patch management. Organizations should also prepare contingency plans for maintaining network security during the patch deployment process, ensuring that critical security functions remain operational even when individual devices are temporarily unavailable. The implementation of robust network monitoring solutions that can detect abnormal TLS 1.3 traffic patterns may help identify exploitation attempts before they cause significant disruption. Additionally, administrators should verify that their Cisco ASA and FTD configurations properly implement TLS version restrictions where possible, potentially disabling TLS 1.3 temporarily until comprehensive security updates are applied across all affected systems.