CVE-2026-20082 in Secure Firewall Adaptive Security Appliance Software
Summary
by MITRE • 03/04/2026
A vulnerability in the handling of the embryonic connection limits in Cisco Secure Firewall Adaptive Security Appliance (ASA) Software could allow an unauthenticated, remote attacker to cause incoming TCP SYN packets to be dropped incorrectly. This vulnerability is due to improper handling of new, incoming TCP connections that are destined to management or data interfaces when the device is under a TCP SYN flood attack. An attacker could exploit this vulnerability by sending a crafted stream of traffic to an affected device. A successful exploit could allow the attacker to prevent all incoming TCP connections to the device from being established, including remote management access, Remote Access VPN (RAVPN) connections, and all network protocols that are TCP-based. This results in a denial of service (DoS) condition for affected features.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 05/05/2026
This vulnerability resides in the Cisco Secure Firewall Adaptive Security Appliance software where the system fails to properly manage embryonic connection limits during TCP SYN flood attacks. The flaw manifests when the device encounters a high volume of incoming TCP SYN packets destined for management or data interfaces, causing the system to incorrectly drop legitimate connection requests. The vulnerability represents a critical weakness in the network device's traffic handling mechanisms, particularly under stress conditions where the system's connection tracking capabilities become overwhelmed. This improper handling of connection limits creates a scenario where legitimate network traffic is mistakenly classified as malicious or excessive, leading to the systematic dropping of valid TCP connections.
The technical implementation of this vulnerability stems from the ASA software's inadequate state management during high-concurrency network events. When subjected to SYN flood attacks, the device's embryonic connection tracking mechanism fails to distinguish between legitimate connection attempts and malicious traffic patterns. This misclassification results in the premature termination of legitimate TCP connections, effectively creating a denial of service condition that impacts all TCP-based services. The flaw specifically affects the device's ability to maintain proper connection state tables under load, causing it to drop incoming SYN packets even when the connection limits have not been legitimately exceeded. This behavior violates fundamental network protocol handling standards and creates a security gap that can be exploited without authentication.
The operational impact of this vulnerability is severe and multifaceted, as it affects critical network services including remote management access, remote access VPN connections, and all TCP-based protocols that depend on the device for connectivity. An attacker exploiting this vulnerability can effectively render the network device unusable by preventing legitimate TCP connections from being established, thereby creating a complete denial of service condition. The vulnerability's exploitation can result in extended network outages that impact business continuity and security operations, as administrators lose access to manage the device remotely and end users experience complete loss of connectivity to services protected by the firewall. This type of attack directly impacts the availability aspect of the CIA triad and can be classified as a network-level DoS attack that targets the fundamental connection handling capabilities of the device.
Organizations should implement multiple layers of defense to mitigate this vulnerability, including rate limiting configurations, connection tracking parameter adjustments, and network segmentation strategies to reduce the attack surface. The Cisco ASA software should be updated to the latest patched versions that address the embryonic connection handling flaw, and administrators should monitor connection statistics to detect potential exploitation attempts. Network administrators should also consider implementing SYN cookies or other TCP protection mechanisms to prevent the exploitation of this vulnerability during attack scenarios. Additionally, organizations should establish monitoring protocols to detect unusual traffic patterns that may indicate SYN flood attacks targeting this specific vulnerability, as the behavior of dropped connections can serve as an indicator of exploitation attempts. This vulnerability aligns with CWE-129 and CWE-131 categories related to improper input validation and insufficient resource pool sizing, and it maps to ATT&CK technique T1498 for network denial of service attacks.