CVE-2024-20495 in ASA
Summary
by MITRE • 10/23/2024
A vulnerability in the Remote Access VPN feature 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 on an affected device.
This vulnerability is due to improper validation of client key data after the TLS session is established. An attacker could exploit this vulnerability by sending a crafted key value to an affected system over the secure TLS session. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.
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Analysis
by VulDB Data Team • 08/01/2025
This vulnerability resides within the Remote Access VPN functionality of Cisco Adaptive Security Appliance and Cisco Firepower Threat Defense software products, representing a critical security flaw that undermines the availability of network infrastructure devices. The issue manifests as an unexpected device reload condition that effectively renders the affected system inaccessible to legitimate users. The vulnerability specifically targets the TLS session handling mechanism where client key data validation occurs after the secure connection has been established, creating a window of opportunity for exploitation that bypasses normal authentication procedures.
The technical root cause stems from inadequate input validation of cryptographic key material within the TLS handshake process. When a client establishes a secure connection to the affected device, the system fails to properly validate the integrity and format of key data provided by the connecting client. This weakness allows an attacker to inject malformed or specially crafted key values that trigger an internal error condition within the device's processing logic. The improper validation occurs at a stage where the system has already authenticated the TLS session but before it has fully processed the cryptographic parameters, creating a logic flaw that can be leveraged for malicious purposes.
From an operational perspective, this vulnerability presents a severe denial of service threat that can be executed remotely without requiring any authentication credentials. The attack vector is particularly dangerous because it can be performed over the network without physical access to the device, making it accessible to any attacker with network connectivity to the affected system. The consequence of a successful exploit is a complete device reload, which disrupts all network services provided by the appliance and requires manual intervention to restore normal operations. This type of vulnerability directly impacts business continuity and can cause cascading effects throughout network infrastructure when critical security devices become unavailable.
The vulnerability maps to CWE-20, "Improper Input Validation," which classifies it as a fundamental flaw in data validation practices within security software implementations. From an adversary perspective, this vulnerability aligns with ATT&CK technique T1499.004, "Endpoint Denial of Service," as it enables attackers to cause system unavailability through manipulation of service parameters. The attack requires minimal privileges since no authentication is needed to trigger the vulnerability, making it particularly attractive to threat actors seeking to disrupt network operations. Organizations should consider implementing network segmentation and monitoring to detect unusual reload patterns that might indicate exploitation attempts.
Mitigation strategies should include immediate deployment of vendor security updates that address the validation logic flaw in the TLS processing code. Network administrators should also implement monitoring solutions that can detect anomalous reload patterns or unusual VPN connection attempts that might indicate exploitation activity. Additional defensive measures include restricting access to VPN services through network access control lists and implementing intrusion detection systems that can identify the specific packet patterns associated with this vulnerability. Organizations should also conduct regular vulnerability assessments to identify other potential weaknesses in their security infrastructure that might be similarly exploitable through improper input validation techniques. The long-term solution involves strengthening input validation procedures across all cryptographic processing components to prevent similar vulnerabilities from emerging in future software releases.