CVE-2006-6870 in avahi
Summary
by MITRE
The consume_labels function in avahi-core/dns.c in Avahi before 0.6.16 allows remote attackers to cause a denial of service (infinite loop) via a crafted compressed DNS response with a label that points to itself.
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Analysis
by VulDB Data Team • 12/22/2016
The vulnerability identified as CVE-2006-6870 affects Avahi versions prior to 0.6.16 and resides within the consume_labels function in avahi-core/dns.c. This flaw represents a classic case of improper input validation and lack of recursion detection in DNS parsing operations. The issue manifests when processing compressed DNS responses where a label contains a self-referencing pointer, creating a circular reference that the parsing function cannot properly handle.
The technical implementation of this vulnerability exploits the DNS compression mechanism used in the Domain Name System to reduce message size. In standard DNS operations, labels can contain pointers to other locations within the same message to avoid repeating domain names. However, when a label points directly to itself, the consume_labels function enters an infinite loop as it attempts to resolve the pointer reference repeatedly without termination conditions. This condition occurs because the function lacks proper cycle detection logic to identify when a pointer reference has already been processed, leading to unbounded resource consumption.
The operational impact of this vulnerability is significant as it enables remote attackers to perform denial of service attacks against Avahi daemon services. When exploited, the infinite loop consumes excessive CPU cycles and memory resources, effectively rendering the affected system unavailable to legitimate users. This vulnerability particularly impacts network services that rely on Avahi for service discovery, such as mDNS (multicast DNS) implementations, making it a critical concern for network infrastructure and IoT devices that utilize Avahi for zero-configuration networking.
From a cybersecurity perspective, this vulnerability aligns with CWE-835, which specifically addresses the issue of infinite loops in software. The attack vector requires only a crafted DNS response packet sent to a vulnerable Avahi service, making it easily exploitable in network environments where Avahi is running. The ATT&CK framework categorizes this as a Denial of Service attack technique under the T1499.004 sub-technique for Network Denial of Service, as it specifically targets network service availability through resource exhaustion.
Mitigation strategies include upgrading to Avahi version 0.6.16 or later, which contains the necessary fixes to detect and prevent recursive pointer references. Network administrators should also implement proper input validation and bounds checking in DNS processing components, along with monitoring for unusual CPU utilization patterns that may indicate exploitation attempts. Additionally, firewalls and network segmentation can help limit the attack surface by restricting access to Avahi services to trusted networks only, reducing the potential impact of such attacks on broader network infrastructure.