CVE-2007-4103 in Asterisk
Summary
by MITRE
The IAX2 channel driver (chan_iax2) in Asterisk Open 1.2.x before 1.2.23, 1.4.x before 1.4.9, and Asterisk Appliance Developer Kit before 0.6.0, when configured to allow unauthenticated calls, allows remote attackers to cause a denial of service (resource exhaustion) via a flood of calls that do not complete a 3-way handshake, which causes an ast_channel to be allocated but not released.
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Analysis
by VulDB Data Team • 08/06/2019
The vulnerability identified as CVE-2007-4103 represents a critical resource exhaustion flaw within the IAX2 channel driver of Asterisk Open Source PBX systems. This vulnerability specifically affects versions prior to 1.2.23 in the 1.2.x series, 1.4.9 in the 1.4.x series, and Asterisk Appliance Developer Kit versions before 0.6.0. The flaw manifests when systems are configured to accept unauthenticated calls, creating an exploitable condition that can be leveraged by remote attackers to disrupt service availability. The issue stems from improper resource management within the channel allocation mechanism, where connections are established but never properly terminated, leading to progressive system resource depletion.
The technical implementation of this vulnerability exploits the IAX2 protocol's three-way handshake mechanism which is designed to establish reliable communication channels between Asterisk servers and clients. When attackers send a flood of connection requests that deliberately fail to complete the handshake process, the system allocates ast_channel structures to manage these incomplete connections. These allocated channels remain in memory indefinitely, creating a memory leak that gradually consumes available system resources. The flaw is classified under CWE-400 as an Uncontrolled Resource Consumption vulnerability, specifically manifesting as a denial of service condition. The attack vector operates entirely over the network without requiring authentication, making it particularly dangerous for systems that expose IAX2 services to untrusted networks.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise entire telephony infrastructure. As the system continues to allocate channels without proper cleanup, memory consumption increases linearly with the number of attack packets, eventually leading to system crashes or severe performance degradation that affects legitimate users. This resource exhaustion can occur rapidly with minimal bandwidth requirements, making it an effective low-cost attack vector against telephony systems. The vulnerability directly maps to ATT&CK technique T1499.004 for Network Denial of Service, where adversaries leverage protocol implementation weaknesses to consume system resources. Organizations running affected Asterisk versions face significant risk of service interruption, particularly those with public IAX2 endpoints or systems that do not properly restrict access to their telephony infrastructure.
Mitigation strategies for CVE-2007-4103 require immediate implementation of both configuration changes and software updates. The primary defense involves upgrading to patched versions of Asterisk Open Source, specifically versions 1.2.23 or later for the 1.2.x series, 1.4.9 or later for the 1.4.x series, and 0.6.0 or later for the Asterisk Appliance Developer Kit. Additionally, system administrators should implement strict access controls to limit IAX2 service exposure, disable unauthenticated calls when possible, and configure appropriate rate limiting mechanisms to prevent flood attacks. Network-level protections such as firewall rules that restrict IAX2 traffic to trusted sources and intrusion detection systems that monitor for anomalous connection patterns can provide additional defense layers. The vulnerability demonstrates the importance of proper resource management in telephony systems and highlights the need for comprehensive security testing of protocol implementations. Organizations should also implement monitoring solutions to detect unusual resource consumption patterns that may indicate exploitation attempts, as the attack is designed to be stealthy while gradually consuming system resources.