CVE-2011-2665 in Asterisk
Summary
by MITRE
reqresp_parser.c in the SIP channel driver in Asterisk Open Source 1.8.x before 1.8.4.3 allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via a SIP packet with a Contact header that lacks a < (less than) character.
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Analysis
by VulDB Data Team • 11/14/2021
The vulnerability described in CVE-2011-2665 represents a critical denial of service flaw within the Asterisk Open Source telephony system, specifically affecting versions 1.8.x prior to 1.8.4.3. This issue resides in the SIP channel driver's request response parser component, which is responsible for processing incoming SIP packets and managing session initiation protocol communications. The vulnerability stems from inadequate input validation within the parsing logic that handles Contact headers in SIP messages, creating a scenario where maliciously crafted packets can trigger system instability and complete daemon termination.
The technical flaw manifests through a NULL pointer dereference condition that occurs when the reqresp_parser.c module encounters a SIP packet containing a Contact header lacking the required less than character <. This fundamental parsing error demonstrates a classic software defect pattern where the application fails to properly validate input data before attempting to dereference pointers. The absence of proper boundary checking and input sanitization allows attackers to craft packets that bypass normal validation routines, leading to memory access violations that crash the entire Asterisk daemon process. This behavior aligns with CWE-476, which categorizes NULL pointer dereference vulnerabilities as a significant class of software defects that can lead to system crashes and service disruption.
The operational impact of this vulnerability extends beyond simple service interruption, as it provides remote attackers with a straightforward method to compromise telephony infrastructure. Organizations relying on Asterisk for voice communication services face substantial risk of unauthorized service disruption, potentially affecting business continuity and customer communication capabilities. The vulnerability's remote exploitability means that attackers need not have physical access to the system, making it particularly dangerous for publicly accessible telephony servers. Network administrators must consider the broader implications for their communication infrastructure, as successful exploitation can result in complete loss of telephony services until the daemon is manually restarted or the system is rebooted.
Mitigation strategies for CVE-2011-2665 should prioritize immediate patch application to upgrade to Asterisk version 1.8.4.3 or later, which contains the necessary code fixes to properly validate Contact header formats. Network segmentation and access control measures can provide additional defense layers by limiting exposure of SIP endpoints to untrusted networks. Implementing proper input validation at multiple levels of the communication stack, including firewall rules that filter malformed SIP packets, can help reduce attack surface. The vulnerability also highlights the importance of robust software testing practices and adherence to secure coding guidelines, particularly in telecommunications software where reliability and availability are paramount. Organizations should also consider implementing intrusion detection systems that can identify and alert on suspicious SIP traffic patterns that may indicate exploitation attempts. This vulnerability serves as a reminder of the critical importance of maintaining up-to-date security patches in telephony infrastructure and demonstrates how seemingly simple parsing flaws can result in significant service disruption.