CVE-2007-5639 in IP Softphone 2050
Summary
by MITRE
The Nortel UNIStim IP Softphone 2050, IP Phone 1140E, and other Nortel IP Phone, Mobile Voice Client, and WLAN Handsets products allow remote attackers to cause a denial of service (device hang) via a flood of Mute and UnMute messages that have a spoofed source IP address for the Signaling Server.
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Analysis
by VulDB Data Team • 11/02/2017
The vulnerability identified as CVE-2007-5639 represents a significant denial of service weakness affecting multiple Nortel IP phone and wireless handset models including the UNIStim IP Softphone 2050 and IP Phone 1140E. This flaw operates at the application layer of the network stack and specifically targets the signaling protocols used by these telecommunications devices. The vulnerability stems from inadequate validation of source IP addresses within the signaling messages that govern mute and unmute functionality, creating a pathway for malicious actors to exploit the system's trust in legitimate communication sources. The affected devices operate under the assumption that signaling messages originating from their configured signaling server are authentic, without sufficient verification mechanisms to detect spoofed addresses.
The technical implementation of this vulnerability exploits the fundamental trust model inherent in VoIP communications where devices accept signaling commands without robust authentication checks. When remote attackers flood the system with spoofed mute and unmute messages, they leverage the fact that these devices lack proper source address validation mechanisms. The spoofed source IP addresses make the devices believe that the malicious signaling commands originate from legitimate sources, causing the phones to process these commands continuously without proper filtering. This results in resource exhaustion and system instability leading to complete device hang conditions where the affected telephony equipment becomes unresponsive and requires manual intervention or power cycling to restore functionality.
The operational impact of this vulnerability extends beyond simple service disruption to encompass broader network reliability concerns within enterprise and industrial telecommunication environments. Organizations relying on Nortel IP phone systems face potential business interruption risks when attackers exploit this weakness, particularly in mission-critical communication scenarios where device availability is paramount. The vulnerability affects multiple device types across different product lines, indicating a systemic flaw in the software implementation rather than isolated component failure. Network administrators must consider that the attack can be executed remotely without requiring physical access to the devices, making it particularly dangerous in environments where network security controls may be insufficient.
From a cybersecurity perspective, this vulnerability aligns with CWE-284 Access Control Issues and represents a classic example of insufficient input validation in network protocols. The attack vector demonstrates characteristics consistent with the MITRE ATT&CK framework under the T1499 technique category for Network Denial of Service, where adversaries exploit weaknesses in network infrastructure to disrupt communication services. The implementation of proper source address validation and authentication mechanisms would significantly mitigate this risk, as would the deployment of network segmentation controls to limit the attack surface. Organizations should implement monitoring solutions that can detect unusual signaling message patterns and establish network access controls that prevent unauthorized devices from communicating with the signaling infrastructure. The vulnerability serves as a reminder of the critical importance of input validation and authentication in telecommunications systems where device availability directly impacts operational continuity and security posture.