CVE-2016-9225 in ASA
Summary
by MITRE
A vulnerability in the data plane IP fragment handler of the Cisco Adaptive Security Appliance (ASA) CX Context-Aware Security module could allow an unauthenticated, remote attacker to cause the CX module to be unable to process further traffic, resulting in a denial of service (DoS) condition. The vulnerability is due to improper handling of IP fragments. An attacker could exploit this vulnerability by sending crafted fragmented IP traffic across the CX module. An exploit could allow the attacker to exhaust free packet buffers in shared memory (SHM), causing the CX module to be unable to process further traffic, resulting in a DoS condition. This vulnerability affects all versions of the ASA CX Context-Aware Security module. Cisco has not released and will not release software updates that address this vulnerability. There are no workarounds that address this vulnerability. Cisco Bug IDs: CSCva62946.
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Analysis
by VulDB Data Team • 11/04/2022
The vulnerability identified as CVE-2016-9225 represents a critical denial of service weakness within Cisco's Adaptive Security Appliance (ASA) CX Context-Aware Security module. This flaw specifically targets the data plane IP fragment handler, which is responsible for processing fragmented internet protocol packets that traverse the security appliance. The vulnerability stems from inadequate handling of IP fragment reassembly mechanisms, creating a pathway for remote attackers to disrupt the normal operation of the CX module. The issue affects all versions of the ASA CX module, making it a widespread concern across deployed security infrastructure. The vulnerability's classification aligns with CWE-129, which addresses improper handling of input boundaries, and specifically relates to issues in network protocol processing where fragment handling is insufficiently validated. The flaw operates at the fundamental level of packet processing within the security appliance, making it particularly dangerous as it can be exploited without authentication credentials.
The technical exploitation of this vulnerability occurs through the deliberate crafting of fragmented IP traffic that is processed by the CX module's data plane. When the module receives these specially crafted fragments, the improper handling causes the system to allocate and manage packet buffers in an inefficient manner. The attack specifically targets shared memory (SHM) resources where free packet buffers are maintained for processing incoming traffic. As the attacker sends maliciously constructed fragmented packets, the CX module's buffer management system becomes overwhelmed, leading to exhaustion of available packet buffers. This process creates a cascading failure where the module cannot allocate new buffers for legitimate traffic processing, effectively rendering the CX functionality non-operational. The vulnerability's exploitation mechanism directly relates to the ATT&CK technique T1498, which involves network denial of service attacks that exhaust system resources. The attack vector is particularly concerning as it requires no authentication and can be executed remotely, making it accessible to any attacker with network access to the affected appliance.
The operational impact of this vulnerability extends beyond simple service disruption, as it fundamentally compromises the security appliance's ability to perform context-aware security functions. When the CX module becomes unable to process further traffic, the entire security posture of the network is weakened, as context-aware features such as application awareness, user identification, and policy enforcement become unavailable. The DoS condition affects not just the CX module itself but can potentially impact the overall performance and reliability of the ASA appliance, as the module's failure can cause cascading effects throughout the security infrastructure. Organizations relying on ASA CX for advanced security features face significant operational challenges when this vulnerability is exploited, as the disruption can occur without warning and may persist until manual intervention occurs. The lack of available software updates or workarounds from Cisco creates a particularly challenging scenario for affected organizations, as they cannot rely on vendor-provided patches to address the issue. This vulnerability demonstrates the critical importance of proper buffer management and input validation in network security appliances, where resource exhaustion attacks can be devastating to operational continuity.
The absence of available fixes or workarounds from Cisco presents a particularly difficult situation for security administrators and network operators who must manage risk exposure. Organizations affected by this vulnerability must consider alternative security strategies such as implementing additional network segmentation, deploying redundant security appliances, or modifying network architecture to reduce reliance on the vulnerable CX module. The vulnerability's persistence across all versions of the ASA CX module indicates that this was a fundamental design flaw rather than an isolated issue, making it more challenging to remediate through simple configuration changes. Security teams should implement monitoring solutions to detect abnormal packet processing patterns that might indicate exploitation attempts, and establish incident response procedures specifically addressing this vulnerability. The lack of vendor support for this issue highlights the importance of maintaining awareness of vendor security advisories and understanding the risks associated with legacy security solutions that may no longer receive updates or patches. Organizations should also consider the broader implications of relying on security appliances with known vulnerabilities that cannot be addressed through standard update mechanisms, as this situation creates long-term security exposure that may require architectural changes to resolve effectively.