CVE-2016-2232 in Asterisk
Summary
by MITRE
Asterisk Open Source 1.8.x, 11.x before 11.21.1, 12.x, and 13.x before 13.7.1 and Certified Asterisk 1.8.28, 11.6 before 11.6-cert12, and 13.1 before 13.1-cert3 allow remote authenticated users to cause a denial of service (uninitialized pointer dereference and crash) via a zero length error correcting redundancy packet for a UDPTL FAX packet that is lost.
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Analysis
by VulDB Data Team • 07/08/2022
The vulnerability identified as CVE-2016-2232 represents a critical denial of service weakness affecting Asterisk Open Source and Certified Asterisk versions across multiple release lines. This flaw manifests in the handling of UDPTL FAX packets where the system processes zero length error correcting redundancy packets that are subsequently lost during transmission. The vulnerability specifically impacts Asterisk versions 1.8.x, 11.x before 11.21.1, 12.x, and 13.x before 13.7.1, along with their certified counterparts. The issue stems from an uninitialized pointer dereference condition that occurs when the system attempts to process malformed UDPTL FAX packets, creating a scenario where legitimate system operations can be disrupted through carefully crafted malicious input.
The technical exploitation of this vulnerability involves authenticated attackers who can leverage the system's failure to properly validate incoming UDPTL FAX packets. When a zero length error correcting redundancy packet is transmitted and subsequently lost, the Asterisk system encounters an uninitialized pointer that leads to an immediate crash. This behavior aligns with CWE-476 which describes null pointer dereference vulnerabilities, and represents a classic example of improper input validation leading to system instability. The flaw operates at the protocol handling layer where the system fails to account for edge cases in packet processing, particularly when dealing with zero length packets that should be rejected or properly handled rather than causing system termination.
The operational impact of this vulnerability extends beyond simple service disruption as it can be leveraged by malicious actors to systematically degrade the availability of telephony services. Organizations relying on Asterisk for voice and fax communications face potential downtime and service interruptions when this vulnerability is exploited. The authenticated nature of the attack means that only users with legitimate access credentials can trigger the vulnerability, but this still represents a significant risk in environments where access controls may be compromised or where insider threats exist. The crash condition affects the entire Asterisk process, potentially requiring manual intervention to restore service and disrupting ongoing communications. This vulnerability particularly impacts businesses that depend heavily on fax services through SIP trunks, as UDPTL FAX transmission is commonly used for document exchange in enterprise telephony environments.
Mitigation strategies for CVE-2016-2232 should prioritize immediate patching of affected systems to the latest available versions that contain the necessary code fixes. Organizations should implement network segmentation to limit access to Asterisk servers and reduce the attack surface for authenticated exploitation attempts. Additionally, monitoring systems should be configured to detect unusual patterns in FAX packet processing that may indicate exploitation attempts. The fix typically involves implementing proper input validation for UDPTL FAX packets and ensuring that zero length error correcting redundancy packets are handled gracefully without causing system crashes. Organizations should also consider implementing rate limiting for FAX packet processing and establishing automated alerting mechanisms to detect system instability. From an ATT&CK framework perspective, this vulnerability maps to T1499.004 which covers network denial of service, and represents a common exploitation pattern where authenticated users leverage protocol implementation flaws to cause service disruption.