CVE-2017-6721 in Wide Area Application Services
Summary
by MITRE
A vulnerability in the ingress processing of fragmented TCP packets by Cisco Wide Area Application Services (WAAS) could allow an unauthenticated, remote attacker to cause the WAASNET process to restart unexpectedly, causing a denial of service (DoS) condition. More Information: CSCvc57428. Known Affected Releases: 6.3(1). Known Fixed Releases: 6.3(0.143) 6.2(3c)6 6.2(3.22).
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Analysis
by VulDB Data Team • 12/30/2020
The vulnerability identified as CVE-2017-6721 represents a critical flaw in Cisco Wide Area Application Services (WAAS) systems that specifically targets the ingress processing of fragmented TCP packets. This weakness exists within the WAASNET process, which serves as the core component responsible for handling network traffic in Cisco WAAS deployments. The issue manifests when the system encounters fragmented TCP packets, which are commonly used in network communications to handle large data transfers that exceed the maximum transmission unit of network segments. The vulnerability affects the processing logic that handles these fragmented packets, creating a condition where the system's stability is compromised through improper handling of network traffic patterns.
The technical implementation of this vulnerability stems from inadequate validation and processing of TCP packet fragments within the WAASNET subsystem. When the system receives fragmented TCP packets, it fails to properly validate the fragment boundaries and sequence numbers, leading to a scenario where malformed or unexpected fragment combinations can trigger an internal process crash. This flaw operates at the network protocol processing layer and specifically impacts how the WAAS device handles TCP segmentation, where the device's ingress packet processing engine does not adequately account for all possible fragment combinations that could occur during normal network operations. The vulnerability is particularly concerning because it can be exploited remotely without requiring authentication, making it accessible to any attacker who can reach the affected WAAS device on its network interfaces.
The operational impact of CVE-2017-6721 creates a significant denial of service condition that can severely disrupt network operations for organizations relying on WAAS for application acceleration and optimization. When the WAASNET process restarts unexpectedly, all active connections through that WAAS device are terminated, forcing network clients to reconnect and potentially causing application disruptions. The DoS condition affects the entire WAAS appliance, as the process restart affects the device's ability to process subsequent network traffic. This vulnerability particularly impacts organizations using WAAS for WAN optimization, where the service is critical for maintaining application performance across distributed networks. The restart of the WAASNET process can occur multiple times, potentially leading to sustained service degradation or complete service unavailability, especially in environments where WAAS is actively processing large volumes of fragmented TCP traffic.
Organizations affected by this vulnerability should prioritize immediate remediation through the application of the patches available in the fixed releases mentioned in the advisory. The recommended fixed versions include 6.3(0.143), 6.2(3c)6, and 6.2(3.22), which contain the necessary code modifications to properly handle fragmented TCP packet processing. Security teams should conduct comprehensive vulnerability assessments to identify all WAAS devices in their environment that are running the affected software versions. Network monitoring should be enhanced to detect potential exploitation attempts, as the vulnerability may be used as part of broader attack campaigns targeting network infrastructure components. The vulnerability aligns with CWE-129, which describes improper validation of input boundaries, and can be mapped to ATT&CK technique T1498, which involves network denial of service attacks. Organizations should also consider implementing network segmentation strategies to limit the potential impact of such vulnerabilities and establish incident response procedures for handling unexpected service restarts in critical network infrastructure components.