CVE-2009-4055 in s800i
Summary
by MITRE
rtp.c in Asterisk Open Source 1.2.x before 1.2.37, 1.4.x before 1.4.27.1, 1.6.0.x before 1.6.0.19, and 1.6.1.x before 1.6.1.11; Business Edition B.x.x before B.2.5.13, C.2.x.x before C.2.4.6, and C.3.x.x before C.3.2.3; and s800i 1.3.x before 1.3.0.6 allows remote attackers to cause a denial of service (daemon crash) via an RTP comfort noise payload with a long data length.
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Analysis
by VulDB Data Team • 05/22/2025
The vulnerability described in CVE-2009-4055 represents a critical denial of service flaw affecting the Asterisk open source telephony platform across multiple version branches. This issue specifically targets the rtp.c component responsible for handling Real-time Transport Protocol packets, which are fundamental to voice communication in VoIP systems. The vulnerability manifests when the system receives an RTP comfort noise payload containing an excessively long data length field, causing the Asterisk daemon to crash and terminate operations. This type of attack falls under the category of resource exhaustion and daemon disruption, directly impacting the availability of telephony services for organizations relying on Asterisk for their communication infrastructure.
The technical flaw stems from inadequate input validation within the RTP packet processing logic. Comfort noise payloads are used in VoIP systems to maintain audio quality during periods of silence or low activity by transmitting periodic noise packets. However, the vulnerable Asterisk versions fail to properly validate the length field within these comfort noise payloads, allowing malicious actors to craft specially crafted packets with oversized data lengths. When the system attempts to process these malformed packets, the unchecked length field triggers buffer overflow conditions or memory corruption within the RTP handling module. This vulnerability is classified as a CWE-121, heap-based buffer overflow, or potentially CWE-787, out-of-bounds write, depending on the specific execution path taken during packet processing. The attack vector is remote and requires no authentication, making it particularly dangerous for systems exposed to the internet or untrusted networks.
The operational impact of this vulnerability extends beyond simple service disruption, potentially affecting critical business communications and emergency services that rely on Asterisk-based systems. Organizations using affected versions may experience unexpected daemon crashes, leading to complete loss of VoIP service until manual intervention and system restart occur. In enterprise environments where Asterisk serves as the primary communication backbone, such attacks can result in significant downtime and productivity loss. The vulnerability is particularly concerning because it affects multiple release branches including both stable and business editions, indicating a widespread issue that required patches across different product lines. Network administrators and security teams must consider this vulnerability as part of their broader threat landscape, especially in environments where VoIP systems are integral to business operations.
Mitigation strategies for CVE-2009-4055 involve immediate patching of all affected Asterisk installations to the patched versions specified in the advisory. Organizations should also implement network-level filtering to restrict RTP traffic from untrusted sources and consider deploying intrusion detection systems that can identify and alert on anomalous RTP packet patterns. The ATT&CK framework categorizes this vulnerability under T1499.004, Network Denial of Service, and T1595.001, Network Infrastructure Compromise, as it enables attackers to disrupt network services through protocol-level exploitation. Additionally, implementing proper input validation and bounds checking in network protocol handlers should be a standard practice for all telephony and communication systems. Regular security assessments and vulnerability scanning should include checks for outdated Asterisk versions, and organizations should maintain updated security patches for their telephony infrastructure to prevent similar issues from arising in the future.