CVE-2024-20293 in ASA
Summary
by MITRE • 05/22/2024
A vulnerability in the activation of an access control list (ACL) on Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to bypass the protection that is offered by a configured ACL on an affected device. This vulnerability is due to a logic error that occurs when an ACL changes from inactive to active in the running configuration of an affected device. An attacker could exploit this vulnerability by sending traffic through the affected device that should be denied by the configured ACL. The reverse condition is also true—traffic that should be permitted could be denied by the configured ACL. A successful exploit could allow the attacker to bypass configured ACL protections on the affected device, allowing the attacker to access trusted networks that the device might be protecting. Note: This vulnerability applies to both IPv4 and IPv6 traffic as well as dual-stack ACL configurations in which both IPv4 and IPv6 ACLs are configured on an interface.
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Analysis
by VulDB Data Team • 07/30/2025
This vulnerability resides in the Cisco Adaptive Security Appliance (ASA) and Cisco Firepower Threat Defense (FTD) software platforms, representing a critical flaw in the access control list activation mechanism that undermines fundamental network security controls. The issue manifests when an access control list transitions from an inactive to active state within the running configuration of an affected device, creating a logic error that compromises the integrity of configured security policies. This represents a direct violation of the principle of least privilege and undermines the core security model that organizations rely upon for network segmentation and access control. The vulnerability affects both IPv4 and IPv6 traffic configurations including dual-stack implementations, making it particularly dangerous as it impacts modern network environments that utilize both protocol versions simultaneously.
The technical exploitation of this vulnerability occurs through a specific logic error that affects the ACL activation process during runtime configuration changes. When an ACL transitions from inactive to active status, the software fails to properly evaluate and enforce the configured access control rules, resulting in a complete bypass of the intended security protections. This flaw creates a temporal window where the device's security policies become inconsistent, allowing unauthorized traffic flows that should be either permitted or denied based on the configured ACL rules. The vulnerability's impact is particularly severe because it affects the fundamental operation of network access control, where traffic that should be denied by the ACL can be permitted, and conversely, traffic that should be permitted can be denied. This creates a bidirectional bypass condition that can be exploited to gain unauthorized access to protected network segments. The flaw affects all versions of the software where ACLs can be dynamically activated, making it a persistent threat across multiple device configurations.
The operational impact of this vulnerability extends far beyond simple network access control bypass, as it fundamentally compromises the security posture of organizations that rely on Cisco ASA and FTD devices for network protection. Attackers can leverage this vulnerability to traverse network boundaries that should be protected by configured ACLs, potentially gaining access to sensitive internal networks, critical infrastructure, or confidential data stores. The vulnerability's ability to affect both IPv4 and IPv6 traffic means that modern dual-stack networks are equally at risk, eliminating any potential protection that might be offered by protocol separation. Organizations may experience unauthorized data exfiltration, lateral movement within their networks, and potential compromise of systems that should be isolated by the configured ACL protections. The vulnerability's remote and unauthenticated nature means that attackers do not require any credentials or privileged access to exploit the flaw, making it particularly dangerous for perimeter security devices that are designed to protect against external threats.
Mitigation strategies for this vulnerability must address the immediate risk while maintaining network functionality and security posture. Cisco has released patches and software updates that correct the logic error in the ACL activation process, requiring organizations to apply these updates as a priority to remediate the vulnerability. Network administrators should implement temporary workarounds such as disabling unused ACLs, implementing additional monitoring for unauthorized traffic patterns, and strengthening other security controls to compensate for the compromised ACL functionality. The vulnerability aligns with several ATT&CK framework techniques including T1046 Network Service Scanning and T1071 Application Layer Protocol, as attackers may use the bypassed access to explore network services and establish persistence within protected segments. From a CWE perspective, this vulnerability maps to CWE-284 Improper Access Control, specifically addressing the inadequate enforcement of access control mechanisms during runtime configuration changes. Organizations should conduct comprehensive network assessments to identify any unauthorized access that may have occurred during the vulnerability window and implement enhanced monitoring for anomalous traffic patterns that could indicate exploitation attempts. The vulnerability underscores the critical importance of maintaining up-to-date security patches and the potential consequences of configuration changes that affect core security mechanisms.