CVE-2007-3372 in Avahi
Summary
by MITRE
The Avahi daemon in Avahi before 0.6.20 allows attackers to cause a denial of service (exit) via empty TXT data over D-Bus, which triggers an assert error.
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Analysis
by VulDB Data Team • 07/20/2021
The vulnerability identified as CVE-2007-3372 affects the Avahi daemon version 0.6.19 and earlier, representing a critical denial of service weakness that can be exploited to terminate the service entirely. This issue specifically manifests when the daemon receives empty TXT data through the D-Bus communication interface, creating a scenario where the system encounters an assertion error that results in the daemon's abrupt exit. The Avahi daemon serves as a crucial component for service discovery in Linux environments, implementing the DNS Service Discovery protocol and Zeroconf networking standards to enable automatic network service detection without centralized configuration. The vulnerability stems from inadequate input validation within the daemon's D-Bus message handling mechanism, where the system fails to properly sanitize or validate TXT record data before processing.
The technical flaw resides in the daemon's failure to handle empty TXT data fields gracefully during D-Bus communication, leading to an assertion failure that terminates the process. According to CWE-248, this represents an improper handling of an exception condition, specifically manifesting as an unchecked assertion error that causes program termination. The vulnerability operates through the D-Bus interface where Avahi listens for service registration and announcement messages, particularly those containing TXT records that are used to publish service metadata. When an attacker crafts a malicious D-Bus message with empty TXT data fields, the daemon's internal assertion checks fail, causing an immediate process exit. This behavior aligns with ATT&CK technique T1499.004, which covers network denial of service attacks through service disruption.
The operational impact of this vulnerability extends beyond simple service interruption, as the Avahi daemon's role in network service discovery means that its termination can cascade into broader network connectivity issues. The daemon typically runs as a system service and is essential for automatic discovery of printers, file shares, and other network services in Linux environments. When the daemon exits due to this assertion error, it leaves the system unable to properly announce or discover network services, potentially disrupting network functionality for all users and applications that depend on Avahi for service discovery. The vulnerability is particularly concerning because it can be triggered remotely through the D-Bus interface without requiring authentication, making it accessible to any attacker with network access to the system. The lack of proper input validation creates a direct path for exploitation that can be automated, potentially leading to repeated service disruption attacks.
Mitigation strategies for CVE-2007-3372 primarily involve upgrading to Avahi version 0.6.20 or later, where the issue has been resolved through improved input validation and assertion handling. System administrators should also implement D-Bus access controls to limit which applications can communicate with the Avahi daemon, reducing the attack surface. The fix typically involves adding proper bounds checking and validation for TXT record data before assertion checks are performed, ensuring that empty or malformed data does not trigger critical errors. Organizations should also consider implementing monitoring for unusual daemon restart patterns that might indicate exploitation attempts, and establish regular patch management procedures to address such vulnerabilities promptly. Additionally, network segmentation and firewall rules can be implemented to restrict D-Bus communication to trusted hosts only, further reducing the risk of exploitation.