CVE-2008-5081 in avahi
Summary
by MITRE
The originates_from_local_legacy_unicast_socket function (avahi-core/server.c) in avahi-daemon in Avahi before 0.6.24 allows remote attackers to cause a denial of service (crash) via a crafted mDNS packet with a source port of 0, which triggers an assertion failure.
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Analysis
by VulDB Data Team • 05/25/2025
The vulnerability identified as CVE-2008-5081 resides within the Avahi daemon implementation, specifically in the avahi-core/server.c file where the originates_from_local_legacy_unicast_socket function fails to properly validate incoming mDNS packets. This flaw affects Avahi versions prior to 0.6.24 and represents a classic input validation issue that can be exploited to trigger a denial of service condition. The vulnerability manifests when a remote attacker crafts a malicious mDNS packet with a source port set to zero, which then causes the daemon to encounter an assertion failure during processing. This type of vulnerability falls under CWE-20, which encompasses improper input validation, and specifically demonstrates how malformed network traffic can lead to application instability. The Avahi daemon serves as a zero-configuration networking implementation that enables automatic discovery of services on local networks, making it a critical component in many networked environments.
The technical exploitation of this vulnerability occurs through the manipulation of the mDNS protocol implementation within Avahi's core server functionality. When the daemon receives a packet with source port zero, the originates_from_local_legacy_unicast_socket function fails to properly handle this edge case, leading to an assertion failure that terminates the daemon process. This assertion failure represents a fundamental breakdown in the software's error handling mechanisms, where the code assumes certain conditions will always be met but encounters an unexpected scenario. The mDNS protocol typically operates over UDP port 5353, and the vulnerability exploits the fact that the daemon does not adequately validate the source port field in incoming packets. This issue directly maps to ATT&CK technique T1499.004, which involves network disruption through protocol manipulation, and demonstrates how network-level attacks can be leveraged to cause service availability issues.
The operational impact of this vulnerability extends beyond simple daemon crashes, as it can disrupt network discovery services that depend on Avahi for proper operation. When the Avahi daemon crashes, it affects the automatic discovery of network services, printers, and other devices that rely on zero-configuration networking. This disruption can cascade into broader network availability issues, particularly in environments where multiple services depend on the seamless operation of Avahi for service registration and discovery. The vulnerability affects both desktop and server environments where Avahi is deployed, creating potential for widespread service disruption in enterprise networks that utilize zero-configuration networking. Organizations running affected versions of Avahi are particularly vulnerable during peak network discovery periods when the daemon is actively processing multicast DNS queries, as attackers can repeatedly exploit this flaw to maintain persistent service disruption. The vulnerability also represents a significant concern for embedded systems and IoT devices that rely on Avahi for network service discovery, as these systems may not have robust recovery mechanisms in place to handle daemon crashes.
Mitigation strategies for CVE-2008-5081 primarily focus on upgrading to Avahi version 0.6.24 or later, where the vulnerability has been addressed through improved input validation and assertion handling. Network administrators should implement proper network segmentation to limit exposure to untrusted networks where such malicious packets could be injected, and deploy intrusion detection systems that can identify and alert on anomalous mDNS traffic patterns. Additionally, implementing rate limiting on mDNS packet processing and monitoring for unusual source port patterns can help detect potential exploitation attempts. The fix implemented in version 0.6.24 involves strengthening the validation logic within the originates_from_local_legacy_unicast_socket function to properly handle edge cases such as source port zero, thereby preventing the assertion failure that previously caused daemon crashes. Organizations should also consider implementing firewall rules that filter out suspicious mDNS traffic originating from unexpected source ports, and regularly audit their network infrastructure for devices running vulnerable versions of Avahi to ensure comprehensive protection against this and similar vulnerabilities.