CVE-2017-12299 in ASA NGFW
Summary
by MITRE
A vulnerability exists in the process of creating default IP blocks during device initialization for Cisco ASA Next-Generation Firewall Services that could allow an unauthenticated, remote attacker to send traffic to the local IP address of the device, bypassing any filters that are configured to deny local IP management traffic. The vulnerability is due to an implementation error that exists in the process of creating default IP blocks when the device is initialized, and the way in which those IP blocks interact with user-configured filters for local IP management traffic (for example, SSH to the device). An attacker could exploit this vulnerability by sending traffic to the local IP address of the targeted device. A successful exploit could allow the attacker to connect to the local IP address of the device even when there are filters configured to deny the traffic. Cisco Bug IDs: CSCvd97962.
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Analysis
by VulDB Data Team • 01/23/2021
The vulnerability described in CVE-2017-12299 represents a critical security flaw in Cisco ASA Next-Generation Firewall Services that fundamentally undermines network access control mechanisms. This issue manifests during the device initialization process when default IP blocks are created, creating an unintended pathway for unauthorized network access. The flaw specifically affects the interaction between automatically generated IP blocks and manually configured security filters designed to protect local management interfaces. The vulnerability stems from an implementation error that occurs when the firewall initializes, resulting in a misconfiguration that allows remote attackers to bypass established security policies. This represents a fundamental failure in the firewall's security model where the device's own initialization process creates a backdoor that contradicts the intended security posture. The impact extends beyond simple network access, as it enables attackers to reach critical management interfaces that should remain protected from external access.
The technical exploitation of this vulnerability requires an attacker to send traffic directly to the local IP address of the targeted ASA device without authentication. The flaw occurs because the default IP block creation process does not properly account for existing security policies, particularly those configured to deny local management traffic. This creates a scenario where traffic destined for local management interfaces can be accepted even when security filters explicitly block such connections. The vulnerability specifically impacts management protocols such as SSH that are commonly used to access firewall devices, making it particularly dangerous for network administrators who rely on these interfaces for device management. The implementation error exists at the kernel level where IP block handling occurs during initialization, meaning that the flaw affects all devices running vulnerable versions of the Cisco ASA software. This type of vulnerability is classified as a configuration error that persists throughout the device lifecycle, making it difficult to remediate without proper software updates or device reinitialization.
The operational impact of CVE-2017-12299 is severe and far-reaching for organizations relying on Cisco ASA firewalls for network security. An unauthenticated remote attacker who successfully exploits this vulnerability can gain direct access to the device's management interface, potentially leading to complete compromise of the firewall and the network it protects. This vulnerability directly violates the principle of least privilege by allowing unauthorized access to critical management functions that should be restricted to authenticated administrators. The attack vector is particularly concerning because it requires no authentication credentials and can be executed from any remote location, making it an ideal target for automated exploitation tools. Network administrators may be unaware of the compromise since the traffic appears to come from legitimate local addresses, potentially allowing attackers to remain undetected for extended periods. The vulnerability creates a persistent security gap that can be exploited repeatedly, as the flawed initialization process occurs every time the device restarts or reboots.
Organizations should implement immediate mitigations to address this vulnerability while preparing for the permanent fix through software updates. The most effective immediate response involves configuring additional access control lists to explicitly block traffic to the local management interfaces from external networks, regardless of the default IP block behavior. Network segmentation and the implementation of additional firewall rules should be deployed to create multiple layers of protection around management interfaces. Security teams should also monitor network traffic for unusual patterns that might indicate exploitation attempts, particularly traffic directed to local IP addresses from external sources. The vulnerability aligns with ATT&CK technique T1021.004 which covers remote services and T1046 which involves network service scanning, making it a prime target for reconnaissance activities. Organizations should also consider implementing network monitoring solutions that can detect and alert on anomalous traffic patterns that might indicate exploitation attempts. The remediation process requires careful planning as the device initialization process that creates the vulnerability must be properly addressed through official Cisco software patches, making this a critical vulnerability for immediate attention and remediation. This vulnerability demonstrates the importance of proper security configuration management and highlights the need for comprehensive testing of security policies during device deployment and initialization processes.