CVE-2015-6421 in WAAS
Summary
by MITRE
cifs-ao in the CIFS optimization functionality on Cisco Wide Area Application Service (WAAS) and Virtual WAAS (vWAAS) devices 5.x before 5.3.5d and 5.4 and 5.5 before 5.5.3 allows remote attackers to cause a denial of service (resource consumption and device reload) via crafted network traffic, aka Bug ID CSCus85330.
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Analysis
by VulDB Data Team • 07/06/2022
The vulnerability identified as CVE-2015-6421 affects the CIFS optimization functionality within Cisco Wide Area Application Service (WAAS) and Virtual WAAS (vWAAS) devices operating on software versions 5.x prior to 5.3.5d, 5.4, and 5.5 prior to 5.5.3. This flaw resides in the cifs-ao component which handles CIFS (Common Internet File System) optimization operations, representing a critical weakness in network infrastructure security. The vulnerability specifically targets the device's resource management mechanisms during CIFS traffic processing, creating a pathway for malicious actors to exploit the system's handling of network packets.
The technical implementation flaw stems from insufficient input validation and resource management within the CIFS optimization module. When the system processes specially crafted network traffic designed to exploit this vulnerability, it fails to properly validate the incoming CIFS packets, leading to resource exhaustion and subsequent device instability. This behavior manifests as excessive memory consumption and CPU utilization, ultimately forcing the device to reload its operating system and resulting in complete service disruption. The vulnerability operates at the network protocol level, leveraging the CIFS optimization functionality to create a resource consumption attack vector that can be executed remotely without authentication requirements.
The operational impact of CVE-2015-6421 extends beyond simple service interruption, as it represents a significant threat to network availability and business continuity. Organizations relying on WAAS and vWAAS devices for application acceleration and bandwidth optimization face potential downtime that could affect critical business applications and user access. The vulnerability's exploitation results in automatic device reloads, causing temporary network disruption that may cascade through dependent systems. This denial of service condition particularly affects enterprises with distributed network architectures where WAAS devices serve as critical components for optimizing file sharing and application performance across wide area networks.
Security professionals should note that this vulnerability aligns with CWE-400, which addresses "Uncontrolled Resource Consumption," and maps to ATT&CK technique T1499.004 for "Endpoint Denial of Service." The attack surface for this vulnerability includes any network segment where CIFS optimization is enabled on affected Cisco devices, making it particularly dangerous in enterprise environments where file sharing and application delivery optimization are common requirements. Organizations should prioritize immediate patching of affected systems to prevent exploitation, as the vulnerability provides attackers with a straightforward method to cause significant service disruption. Additionally, network segmentation and access control measures should be implemented to limit exposure to this vulnerability, while monitoring systems should be configured to detect anomalous resource consumption patterns that may indicate exploitation attempts.
Cisco has addressed this vulnerability through software updates and patches for the affected versions, requiring administrators to upgrade to versions 5.3.5d, 5.4, or 5.5.3 and later. The remediation process should include thorough testing of the updated firmware in controlled environments before deployment to production systems. Network administrators should also implement monitoring solutions to detect unusual traffic patterns that might indicate attempts to exploit this vulnerability, as the attack does not require authentication and can be executed from external network segments.