CVE-2024-20402 in ASA
Summary
by MITRE • 10/23/2024
A vulnerability in the SSL VPN feature for Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause an affected device to reload unexpectedly, resulting in a denial of service (DoS) condition.
This vulnerability is due to a logic error in memory management when the device is handling SSL VPN connections. An attacker could exploit this vulnerability by sending crafted SSL/TLS packets to the SSL VPN server of the affected device. 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 • 07/15/2025
The vulnerability identified as CVE-2024-20402 represents a critical denial of service weakness within Cisco's Adaptive Security Appliance and Firepower Threat Defense software platforms. This flaw specifically targets the SSL VPN functionality, which serves as a crucial remote access mechanism for organizations relying on Cisco security infrastructure. The vulnerability stems from a fundamental logic error in the memory management subsystem of these devices, creating a condition where legitimate network traffic can trigger catastrophic system behavior. The affected devices operate under the assumption that certain memory allocation patterns will remain consistent during SSL VPN session handling, but this assumption fails when confronted with carefully crafted malicious input.
The technical exploitation mechanism involves sending specifically crafted SSL/TLS packets to the SSL VPN server component of the affected Cisco appliances. These packets are designed to trigger the memory management logic error, causing the device to enter an unstable state where it must restart its entire operating system to recover from the condition. The vulnerability does not require authentication credentials or privileged access, making it particularly dangerous as any remote attacker can potentially exploit this weakness. The memory management flaw likely involves improper handling of memory allocation, deallocation, or reference counting during SSL VPN connection establishment or maintenance phases, creating a scenario where the device's memory pool becomes corrupted or exhausted.
From an operational impact perspective, this vulnerability creates significant business disruption potential for organizations relying on Cisco ASA and FTD devices for their network security infrastructure. The unexpected device reloads can occur at any time, potentially during critical network operations or security monitoring activities, leading to extended periods of network unavailability. The DoS condition affects not just the SSL VPN functionality but can also impact other services running on the same appliance, as the device restart process typically affects the entire system. Organizations may experience loss of network visibility, interruption of remote access capabilities, and potential security gaps during the device recovery period. The vulnerability essentially allows attackers to perform a form of service disruption that can be difficult to detect and mitigate in real-time.
Security professionals should consider this vulnerability in the context of the MITRE ATT&CK framework, specifically mapping it to the privilege escalation and denial of service tactics. The vulnerability could potentially be leveraged as part of broader attack campaigns where initial access is achieved through other means, and this DoS capability is used to disrupt network operations or create cover for more sophisticated attacks. Organizations should implement immediate mitigations including disabling SSL VPN functionality when not required, applying the latest security patches from Cisco, and monitoring network traffic for anomalous SSL/TLS patterns that might indicate exploitation attempts. The vulnerability also aligns with CWE-129, which addresses improper validation of array index bounds, as the memory management error likely involves incorrect handling of memory allocation boundaries during SSL VPN processing. Network segmentation and redundant security appliances should be considered as additional protective measures to ensure continued network availability during potential exploitation events.