CVE-2019-15256 in ASA
Summary
by MITRE
A vulnerability in the Internet Key Exchange version 1 (IKEv1) feature of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to trigger a reload of an affected device, resulting in a denial of service (DoS) condition. The vulnerability is due to improper management of system memory. An attacker could exploit this vulnerability by sending malicious IKEv1 traffic to an affected device. The attacker does not need valid credentials to authenticate the VPN session, nor does the attacker's source address need to match a peer statement in the crypto map applied to the ingress interface of the affected device. An exploit could allow the attacker to exhaust system memory resources, leading to a reload of an affected device.
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Analysis
by VulDB Data Team • 12/29/2023
The vulnerability described in CVE-2019-15256 represents a critical denial of service weakness within Cisco's security infrastructure products, specifically affecting the Internet Key Exchange version 1 implementation in Adaptive Security Appliance and Firepower Threat Defense software. This flaw resides in the IKEv1 protocol handling mechanism where the system fails to properly manage memory allocation during the processing of incoming IKEv1 messages. The vulnerability operates at the network protocol level, targeting the foundational security mechanisms that establish encrypted communication tunnels between network devices. The affected systems include various Cisco ASA and FTD software versions where IKEv1 functionality is enabled, making this a widespread concern across enterprise security deployments that rely on these platforms for network protection.
The technical exploitation of this vulnerability occurs through malformed IKEv1 traffic that triggers improper memory handling within the affected software implementations. The flaw stems from inadequate input validation and memory management practices during IKEv1 message processing, specifically when handling certain packet structures or sequence numbers that cause the system to allocate memory resources without proper bounds checking. According to CWE classification, this vulnerability maps to CWE-129 Input Validation and Replication, as the system fails to validate the integrity of incoming IKEv1 messages before processing them. The attack vector requires only network access to the vulnerable device, making it particularly dangerous as it can be executed from external networks without requiring authentication credentials or matching peer configurations. The attacker's source address does not need to match any configured crypto map entries, eliminating the need for sophisticated network reconnaissance or configuration matching.
The operational impact of this vulnerability extends beyond simple service disruption, as it can cause complete device reloads that effectively deny network security services for extended periods. When exploited successfully, the malicious IKEv1 traffic consumes system memory resources to the point of exhaustion, forcing the device to automatically reboot as a protective mechanism. This behavior creates a cascading effect in network security infrastructure, where the DoS condition can disrupt critical network communications and leave the organization vulnerable to other attacks during the recovery period. The vulnerability affects both ASA and FTD platforms, with the potential for widespread disruption across enterprise networks that depend on these devices for secure remote access and network segmentation. From an ATT&CK framework perspective, this vulnerability aligns with T1499.004 Network Denial of Service and T1566.001 Phishing via Social Engineering, as it can be leveraged for network disruption attacks without requiring complex credential acquisition.
Mitigation strategies for CVE-2019-15256 should focus on immediate network segmentation and access control measures to prevent unauthorized traffic from reaching vulnerable devices. Organizations should implement firewall rules to block IKEv1 traffic on affected interfaces, particularly on external boundaries where the attack surface is largest. The most effective immediate solution involves disabling IKEv1 functionality on affected devices when possible, though this may require careful planning to maintain existing VPN services. Cisco has released software updates addressing this vulnerability, and organizations should prioritize applying these patches to maintain system integrity. Network monitoring should be enhanced to detect unusual IKEv1 traffic patterns that may indicate exploitation attempts, while also implementing rate limiting on IKEv1 message processing to prevent memory exhaustion. The vulnerability highlights the importance of proper memory management in security appliances and underscores the need for robust input validation in protocol implementations. Regular security assessments of network infrastructure should include verification of IKEv1 configurations and monitoring for potential exploitation indicators.