CVE-2018-19278 in Asterisk
Summary
by MITRE
Buffer overflow in DNS SRV and NAPTR lookups in Digium Asterisk 15.x before 15.6.2 and 16.x before 16.0.1 allows remote attackers to crash Asterisk via a specially crafted DNS SRV or NAPTR response, because a buffer size is supposed to match an expanded length but actually matches a compressed length.
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Analysis
by VulDB Data Team • 06/06/2023
This vulnerability exists in Digium Asterisk versions 15.x before 15.6.2 and 16.x before 16.0.1, specifically affecting DNS SRV and NAPTR lookup functionality. The issue stems from improper buffer handling during DNS resolution processes where the system allocates memory based on compressed DNS response lengths rather than the actual expanded lengths that occur during decompression. This fundamental mismatch creates a classic buffer overflow condition that remote attackers can exploit to crash the Asterisk service. The vulnerability operates at the network protocol level within the DNS resolution subsystem, making it particularly dangerous as it can be triggered through normal SIP signaling operations that rely on DNS lookups for call routing and registration.
The technical flaw manifests when Asterisk processes DNS SRV or NAPTR responses that contain compressed domain names. During normal DNS processing, domain names are typically compressed using pointers to reduce message size, but when these compressed responses are expanded back to their full form for processing, the allocated buffer size remains based on the compressed length rather than the expanded length. This discrepancy allows attackers to craft malicious DNS responses where the compressed length appears reasonable but the expanded length exceeds the allocated buffer capacity. When the DNS resolution code attempts to copy the expanded data into the insufficiently sized buffer, it overflows into adjacent memory regions, causing unpredictable behavior and ultimately service disruption.
The operational impact of this vulnerability extends beyond simple service disruption as it can be leveraged in broader attack scenarios targeting VoIP infrastructure. Remote attackers can exploit this weakness to perform denial of service attacks against Asterisk servers, potentially disrupting critical communication services for businesses and organizations relying on these systems. The vulnerability is particularly concerning in environments where Asterisk serves as a core component of PBX systems, as it can lead to complete communication outages. Additionally, the crash condition can potentially be chained with other vulnerabilities to achieve more sophisticated attack objectives, though the primary risk remains service availability and reliability.
Mitigation strategies should focus on immediate patch application to the affected Asterisk versions, with administrators prioritizing updates to 15.6.2 or 16.0.1 respectively. Network administrators should also implement DNS response validation measures and consider deploying DNS filtering solutions to prevent malformed responses from reaching Asterisk systems. The vulnerability aligns with CWE-121, heap-based buffer overflow, and can be mapped to ATT&CK technique T1499.004, Network Denial of Service, through the use of crafted DNS responses to cause service disruption. Organizations should also implement monitoring for unusual DNS traffic patterns and establish incident response procedures to handle potential exploitation attempts, as the vulnerability can be difficult to detect through normal network monitoring due to its indirect nature through legitimate DNS resolution processes.