CVE-2024-20299 in ASA
Summary
by MITRE • 10/23/2024
A vulnerability in the AnyConnect firewall for Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to bypass a configured access control list (ACL) and allow traffic that should have been denied to flow through an affected device. This vulnerability is due to a logic error in populating group ACLs when an AnyConnect client establishes a new session toward an affected device. An attacker could exploit this vulnerability by establishing an AnyConnect connection to the affected device. A successful exploit could allow the attacker to bypass configured ACL rules.
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Analysis
by VulDB Data Team • 08/01/2025
This vulnerability exists within Cisco's Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) platforms, specifically affecting the AnyConnect VPN client functionality. The issue stems from a fundamental logic error in how group access control lists are populated during new AnyConnect session establishment processes. When an AnyConnect client connects to an affected device, the system fails to properly validate or enforce the configured ACL rules that should normally restrict traffic flow based on predefined security policies. This represents a critical failure in the network's security enforcement mechanisms, effectively creating a backdoor that allows unauthorized traffic to bypass normal access controls.
The technical flaw manifests as a logic error in the group ACL population process, where the system does not correctly apply or enforce the security policies that should normally be enforced at the network boundary. This vulnerability operates at the session establishment phase of the AnyConnect protocol, meaning that an attacker who can establish a connection to the device can potentially bypass all configured ACL rules. The flaw does not require authentication to exploit, making it particularly dangerous as any remote attacker can potentially leverage this weakness. The vulnerability affects the core security enforcement functionality of the device, undermining the fundamental principle of network segmentation and access control that these appliances are designed to provide.
The operational impact of this vulnerability is severe and far-reaching for organizations relying on Cisco ASA and FTD devices for network security. An attacker who successfully exploits this vulnerability can gain unauthorized access to network resources that should be restricted by ACL rules, potentially leading to lateral movement within the network, data exfiltration, or further exploitation of other systems. The vulnerability essentially allows attackers to establish a foothold that bypasses the very security controls that should prevent such access. This could result in significant compromise of network integrity, confidentiality, and availability, particularly in environments where strict access controls are critical for compliance and security posture. The attack surface expands significantly as this affects all AnyConnect sessions, potentially impacting remote workforce access while simultaneously weakening network perimeter defenses.
Organizations should implement immediate mitigations including applying the latest security patches from Cisco, which address the logic error in group ACL population. Network administrators should also consider implementing additional monitoring controls to detect anomalous AnyConnect session establishment patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-284 Access Control Bypass, specifically targeting improper access control enforcement mechanisms. From an ATT&CK perspective, this vulnerability maps to T1078 Valid Accounts and T1566 Phishing, as it could enable attackers to establish persistent access through legitimate VPN connections while potentially supporting further reconnaissance and lateral movement activities. Organizations should also review their existing security monitoring procedures to ensure they can detect unauthorized traffic patterns that might indicate successful exploitation of this vulnerability.