CVE-2008-1923 in Asterisk
Summary
by MITRE
The IAX2 channel driver (chan_iax2) in Asterisk 1.2 before revision 72630 and 1.4 before revision 65679, when configured to allow unauthenticated calls, sends "early audio" to an unverified source IP address of a NEW message, which allows remote attackers to cause a denial of service (traffic amplification) via a spoofed NEW message.
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Analysis
by VulDB Data Team • 07/31/2021
The vulnerability identified as CVE-2008-1923 resides within the IAX2 channel driver implementation of Asterisk versions prior to specific revisions, creating a significant security flaw that enables traffic amplification attacks. This issue specifically affects Asterisk 1.2 before revision 72630 and 1.4 before revision 65679, where the system's configuration allows unauthenticated calls to proceed without proper verification mechanisms.
The technical flaw manifests in the improper handling of NEW messages within the IAX2 protocol implementation. When an unauthenticated call is initiated, the system sends "early audio" data to the source IP address specified in the NEW message header without validating the authenticity of the originating address. This design decision creates a fundamental weakness where attackers can exploit the lack of source address verification to manipulate the system's behavior. The vulnerability stems from the absence of proper authentication checks and source validation mechanisms that should occur before any media stream initiation.
The operational impact of this vulnerability is severe and directly enables denial of service attacks through traffic amplification techniques. Remote attackers can craft spoofed NEW messages with malicious source IP addresses, causing the vulnerable Asterisk system to forward audio streams to unintended recipients. This creates a massive amplification effect where a single attack message can generate multiple responses, overwhelming network resources and potentially disrupting legitimate communication services. The attack vector leverages the inherent trust model of the IAX2 protocol implementation, where the system assumes the source IP address in NEW messages is legitimate without proper verification.
This vulnerability maps directly to CWE-284, which addresses improper access control, and aligns with ATT&CK technique T1498, specifically focusing on network denial of service attacks. The flaw represents a classic case of insufficient input validation and trust assumptions in network protocols. The attack demonstrates how protocol-level weaknesses can be exploited to create cascading effects that amplify the impact of simple spoofing attempts. Organizations utilizing Asterisk systems in environments where unauthenticated calls are permitted face significant risk of being used as amplification points in larger distributed denial of service campaigns.
The recommended mitigations include applying the specific patches and revisions mentioned in the vulnerability description, updating to versions that implement proper source address validation for NEW messages. Additionally, system administrators should consider disabling unauthenticated call functionality when possible, implementing proper network segmentation, and deploying rate limiting mechanisms to prevent excessive traffic generation. Network monitoring should be enhanced to detect unusual patterns of early audio transmission and spoofed IP address activity. The fix requires modifications to the chan_iax2 module to validate source addresses before sending early audio, implementing proper authentication checks, and ensuring that the system does not blindly trust information contained in NEW message headers.