CVE-2024-20331 in ASA
Summary
by MITRE • 10/23/2024
A vulnerability in the session authentication functionality of the Remote Access SSL VPN feature of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to prevent users from authenticating.
This vulnerability is due to insufficient entropy in the authentication process. An attacker could exploit this vulnerability by determining the handle of an authenticating user and using it to terminate their authentication session. A successful exploit could allow the attacker to force a user to restart the authentication process, preventing a legitimate user from establishing remote access VPN sessions.
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Analysis
by VulDB Data Team • 10/23/2024
The vulnerability identified as CVE-2024-20331 represents a critical weakness in the session authentication mechanisms of Cisco's Adaptive Security Appliance and Firepower Threat Defense platforms. This flaw specifically targets the Remote Access SSL VPN functionality where insufficient entropy in the authentication process creates exploitable conditions for malicious actors. The vulnerability stems from predictable session handling that allows attackers to manipulate authentication flows without requiring valid credentials or prior access to the system. Security researchers have classified this issue under CWE-330, which addresses insufficient entropy in random number generation, making it particularly dangerous in authentication contexts where unpredictability is essential for security.
The technical implementation of this vulnerability exploits the deterministic nature of session handle generation within the authentication framework. When users initiate VPN authentication attempts, the system assigns session identifiers that lack sufficient randomness to prevent attackers from predicting or determining valid session handles. This weakness enables an attacker positioned outside the network to observe legitimate authentication sessions and subsequently use their knowledge of session handles to forcibly terminate active authentication processes. The mechanism operates through the manipulation of session state management, where the attacker can send termination requests using discovered session identifiers, effectively disrupting legitimate user access attempts. This type of attack aligns with techniques described in the MITRE ATT&CK framework under T1566 for credential access and T1071 for application layer protocols.
The operational impact of CVE-2024-20331 extends beyond simple denial of service conditions to create persistent access barriers for legitimate users attempting remote network access. When exploited successfully, the vulnerability prevents authenticated users from completing their VPN connection establishment, forcing them to restart the entire authentication process repeatedly. This creates a cascading effect where users may experience extended downtime, reduced productivity, and potential business disruption. Organizations relying on remote access capabilities for business continuity face significant operational challenges, as the vulnerability can be exploited at scale to impact multiple users simultaneously. The attack requires minimal privileges and can be executed remotely, making it particularly dangerous for organizations with distributed workforces or those relying heavily on remote access for critical business operations.
Organizations must implement immediate mitigations to address this vulnerability through multiple defensive layers. The primary recommendation involves updating affected Cisco ASA and FTD devices to patched software versions that correct the entropy generation issues in session handling. Network administrators should also consider implementing additional monitoring controls to detect unusual authentication termination patterns that might indicate exploitation attempts. Configuration changes including enhanced session timeout settings and improved logging of authentication events can provide early warning capabilities. The vulnerability demonstrates the importance of cryptographic randomness in security protocols, emphasizing that insufficient entropy in session management can undermine entire authentication frameworks. Organizations should conduct comprehensive vulnerability assessments to identify all affected systems and implement network segmentation to limit the potential impact of exploitation attempts. Regular security audits of authentication mechanisms and adherence to NIST guidelines for cryptographic key management practices should be maintained to prevent similar vulnerabilities from emerging in future deployments.