CVE-2008-5558 in Asterisk
Summary
by MITRE
Asterisk Open Source 1.2.26 through 1.2.30.3 and Business Edition B.2.3.5 through B.2.5.5, when realtime IAX2 users are enabled, allows remote attackers to cause a denial of service (crash) via authentication attempts involving (1) an unknown user or (2) a user using hostname matching.
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Analysis
by VulDB Data Team • 08/03/2021
The vulnerability described in CVE-2008-5558 represents a critical denial of service flaw affecting Asterisk Open Source versions 1.2.26 through 1.2.30.3 and Business Edition versions B.2.3.5 through B.2.5.5. This issue specifically manifests when the realtime IAX2 users feature is enabled, creating a condition where remote attackers can exploit authentication mechanisms to crash the Asterisk service. The vulnerability operates through two distinct attack vectors involving authentication attempts that target unknown users or users utilizing hostname matching, both of which can trigger the same destabilizing behavior in the system.
The technical flaw stems from inadequate input validation and error handling within the IAX2 authentication subsystem of Asterisk. When realtime IAX2 users are enabled, the system processes authentication requests through a mechanism that fails to properly sanitize or validate user credentials before attempting to match them against the configured user database. This weakness allows attackers to craft malicious authentication attempts that exploit memory handling issues within the IAX2 channel driver. The vulnerability specifically targets the way Asterisk handles authentication failures, particularly when processing unknown users or hostname matching scenarios, leading to memory corruption or improper resource deallocation that results in a complete service crash.
From an operational impact perspective, this vulnerability presents a significant risk to organizations relying on Asterisk for voice communication services, as it can be exploited remotely without requiring authentication credentials. The denial of service condition effectively renders the telephony service unavailable, disrupting business communications and potentially affecting critical operations that depend on voice infrastructure. The remote exploit nature means that attackers can trigger the vulnerability from any network location, making it particularly dangerous in environments where Asterisk systems are exposed to public networks or lack proper network segmentation. This vulnerability directly violates the principle of system availability and can be leveraged as part of broader attack campaigns targeting telephony infrastructure.
The attack pattern associated with CVE-2008-5558 aligns with common denial of service exploitation techniques and can be categorized under CWE-121, heap-based buffer overflow, or CWE-122, stack-based buffer overflow, depending on the specific memory corruption mechanism. The vulnerability also maps to ATT&CK technique T1499.004, "Endpoint Denial of Service," as it targets system resources to prevent legitimate use of telephony services. Organizations should implement immediate mitigations including disabling realtime IAX2 users when not required, applying the relevant security patches from Asterisk releases, and implementing network-level restrictions to limit access to IAX2 ports. Additionally, monitoring for unusual authentication patterns and implementing intrusion detection systems can help identify exploitation attempts before they succeed in causing service disruption.