CVE-2018-15397 in ASA
Summary
by MITRE
A vulnerability in the implementation of Traffic Flow Confidentiality (TFC) over IPsec functionality in 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 restart unexpectedly, resulting in a denial of service (DoS) condition. The vulnerability is due to an error that may occur if the affected software renegotiates the encryption key for an IPsec tunnel when certain TFC traffic is in flight. An attacker could exploit this vulnerability by sending a malicious stream of TFC traffic through an established IPsec tunnel on an affected device. A successful exploit could allow the attacker to cause a daemon process on the affected device to crash, which could cause the device to crash and result in a DoS condition.
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Analysis
by VulDB Data Team • 11/26/2024
The vulnerability identified as CVE-2018-15397 represents a critical denial of service weakness within Cisco's security infrastructure products, specifically affecting the Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) platforms. This flaw manifests in the Traffic Flow Confidentiality (TFC) implementation over IPsec functionality, which is designed to obscure traffic patterns and prevent adversaries from inferring sensitive information about network communications. The TFC mechanism operates by introducing deliberate traffic noise to mask the actual flow of data, but this feature has been compromised by a fundamental implementation error that creates instability in the system's cryptographic operations. The vulnerability exists in the software's handling of encryption key renegotiation processes when TFC traffic is actively flowing through IPsec tunnels, creating a condition where normal network operations can trigger system instability.
The technical exploitation of this vulnerability occurs through a carefully crafted malicious traffic stream that specifically targets the IPsec tunnel renegotiation process during active TFC traffic transmission. When an attacker successfully sends such traffic through an established IPsec tunnel on an affected device, the system's handling of the encryption key renegotiation triggers an error condition that causes a daemon process to crash. This daemon process failure cascades through the system architecture, ultimately leading to a complete device crash and subsequent denial of service condition. The vulnerability's exploitation requires only unauthenticated remote access and does not demand elevated privileges or complex attack vectors, making it particularly dangerous as it can be leveraged by any remote attacker with network access to the affected device. The error condition specifically impacts the IPsec daemon responsible for maintaining secure communications, which is a core component of the device's security functionality.
From an operational impact perspective, this vulnerability creates a severe disruption to network security infrastructure, as affected Cisco ASA and FTD devices become completely unavailable during the crash and subsequent restart cycles. The DoS condition affects not only the immediate device but also compromises the overall network security posture by eliminating the device's ability to enforce security policies and inspect traffic. Organizations relying on these security appliances for network protection face potential exposure to other attacks during the device downtime, as the security appliance becomes unavailable to monitor and control network traffic flow. The vulnerability's impact extends beyond simple service disruption to include potential data exposure risks, as the device's security functions are temporarily suspended during the crash event. Network administrators must also contend with the operational overhead of monitoring for exploitation attempts and managing the recovery process for affected devices.
Security mitigations for CVE-2018-15397 should prioritize immediate patch deployment from Cisco, as the vendor has released software updates specifically addressing the TFC implementation error. Organizations should also implement network segmentation strategies to limit the attack surface and prevent unauthorized access to IPsec tunnels that may be vulnerable to exploitation. Monitoring for unusual traffic patterns that could indicate TFC traffic manipulation attempts should be enabled, and network administrators should consider temporarily disabling TFC functionality on affected devices until patches are deployed. The vulnerability aligns with CWE-209, which describes errors in handling of encryption key management, and relates to ATT&CK technique T1499.004 for network denial of service attacks. Additionally, this vulnerability demonstrates characteristics of the broader category of configuration weaknesses that can lead to privilege escalation and system instability, as outlined in various cybersecurity frameworks and standards for secure network device management. Organizations should also implement redundant security infrastructure to maintain network protection during the patching process and ensure that monitoring systems can detect the specific exploitation patterns associated with this vulnerability.