CVE-2015-0615 in Unity Connection
Summary
by MITRE
The call-handling implementation in Cisco Unity Connection 8.5 before 8.5(1)SU7, 8.6 before 8.6(2a)SU4, 9.x before 9.1(2)SU2, and 10.0 before 10.0(1)SU1, when SIP trunk integration is enabled, allows remote attackers to cause a denial of service (port consumption) by improperly terminating SIP sessions, aka Bug ID CSCul28089.
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Analysis
by VulDB Data Team • 05/02/2022
The vulnerability described in CVE-2015-0615 represents a critical denial of service weakness within Cisco Unity Connection's SIP session management implementation. This flaw specifically affects versions of Cisco Unity Connection running before the mentioned service pack releases, creating a pathway for remote attackers to exploit the system's handling of SIP (Session Initiation Protocol) sessions. The vulnerability manifests when SIP trunk integration is enabled, making it particularly concerning for organizations relying on unified communications infrastructure. The issue stems from the improper termination of SIP sessions, which leads to sustained port consumption and ultimately system resource exhaustion.
The technical root cause of this vulnerability lies in the insufficient validation and handling of SIP session termination sequences within the Cisco Unity Connection platform. When attackers send malformed or improperly terminated SIP messages to the system, the platform fails to properly release associated network resources and ports. This creates a resource leak condition where network ports remain occupied indefinitely, preventing legitimate SIP sessions from establishing. The flaw operates at the protocol level where SIP session management should properly clean up resources upon session termination, but instead maintains references to closed sessions. This behavior aligns with CWE-400, which categorizes resource exhaustion vulnerabilities as a critical weakness in software design and implementation.
The operational impact of this vulnerability extends beyond simple service disruption, creating a persistent threat to unified communications infrastructure. Organizations utilizing Cisco Unity Connection with SIP trunk integration face the risk of sustained denial of service conditions where legitimate users cannot establish voice or video communications. The port consumption effect means that the system gradually becomes less responsive as more resources are consumed, potentially leading to complete system failure. Attackers can maintain this attack with minimal resources and effort, making it particularly dangerous for mission-critical communication systems. The vulnerability also impacts the broader communication ecosystem as it affects the reliability of SIP trunk services and can cascade into other integrated systems that depend on stable communication infrastructure.
Organizations affected by this vulnerability should immediately implement mitigations including applying the recommended service packs and patches provided by Cisco. The vendor released specific updates addressing the SIP session termination handling, including the service pack releases mentioned in the CVE description. Network administrators should also consider implementing SIP-specific firewalls and rate limiting mechanisms to prevent excessive session termination attempts. Monitoring systems should be enhanced to detect unusual port consumption patterns and abnormal SIP session termination behaviors. Additionally, organizations should review their SIP trunk configurations and implement proper session timeout mechanisms. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique for network denial of service attacks, while also demonstrating characteristics of T1566.001 for initial access through network services. The vulnerability highlights the importance of proper resource management in telecommunications systems and demonstrates how protocol-level flaws can create persistent security risks in enterprise communication infrastructure.