CVE-2011-2535 in Asterisk
Summary
by MITRE
chan_iax2.c in the IAX2 channel driver in Asterisk Open Source 1.4.x before 1.4.41.1, 1.6.2.x before 1.6.2.18.1, and 1.8.x before 1.8.4.3, and Asterisk Business Edition C.3 before C.3.7.3, accesses a memory address contained in an option control frame, which allows remote attackers to cause a denial of service (daemon crash) or possibly have unspecified other impact via a crafted frame.
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Analysis
by VulDB Data Team • 11/14/2021
The vulnerability described in CVE-2011-2535 represents a critical memory access flaw within the IAX2 channel driver of Asterisk Open Source and Business Edition products. This issue affects multiple versions of the Asterisk telephony platform, specifically targeting the chan_iax2.c component that handles IAX2 protocol communications. The vulnerability stems from improper validation of option control frames received during IAX2 protocol operations, creating a potential attack surface for remote exploitation. The affected versions include Asterisk 1.4.x before 1.4.41.1, 1.6.2.x before 1.6.2.18.1, 1.8.x before 1.8.4.3, and Business Edition C.3 before C.3.7.3, indicating a widespread impact across the platform's major release lines.
The technical flaw manifests when the IAX2 channel driver processes maliciously crafted option control frames that contain invalid memory addresses or malformed data structures. This improper handling leads to memory access violations that can result in daemon crashes and complete system denial of service. The vulnerability is classified as a buffer over-read or invalid memory access condition, which falls under CWE-125 - Out-of-bounds Read and CWE-787 - Out-of-bounds Write, depending on the specific execution path. Attackers can exploit this weakness by sending specially crafted IAX2 frames that cause the Asterisk daemon to access memory locations outside the intended bounds, potentially leading to crashes or more severe consequences.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it can potentially allow attackers to execute arbitrary code or cause system instability. When the daemon crashes due to memory access violations, legitimate users lose access to telephony services, creating significant business disruption for organizations relying on Asterisk for their communication infrastructure. The vulnerability affects both the availability and integrity of the telephony system, as the crash can occur at any time during normal operation, potentially during critical communication events. Organizations using IAX2-based telephony systems face the risk of sustained service disruption and potential data loss from system restarts.
Mitigation strategies for CVE-2011-2535 focus primarily on applying the vendor-provided patches and updates that address the memory access validation issues in the IAX2 channel driver. System administrators should immediately upgrade to the patched versions of Asterisk, specifically versions 1.4.41.1, 1.6.2.18.1, 1.8.4.3, and Business Edition C.3.7.3 or later. Network-level defenses should include implementing firewall rules to restrict IAX2 traffic to trusted sources only, as the vulnerability is exploitable over the network. Additionally, monitoring and logging of IAX2 protocol communications can help detect anomalous frame patterns that may indicate attempted exploitation. The ATT&CK framework categorizes this vulnerability under T1499 - Endpoint Denial of Service and T1595 - Active Scanning, as attackers would need to actively scan for vulnerable systems and craft specific malicious frames to exploit the memory access flaw. Organizations should also consider implementing intrusion detection systems that can identify suspicious IAX2 frame patterns and provide early warning of potential exploitation attempts.