CVE-2019-9747 in tinysvcmdns
Summary
by MITRE
In tinysvcmdns through 2018-01-16, a maliciously crafted mDNS (Multicast DNS) packet triggers an infinite loop while parsing an mDNS query. When mDNS compressed labels point to each other, the function uncompress_nlabel goes into an infinite loop trying to analyze the packet with an mDNS query. As a result, the mDNS server hangs after receiving the malicious mDNS packet. NOTE: the product's web site states "This project is un-maintained, and has been since 2013. ... There are known vulnerabilities ... You are advised to NOT use this library for any new projects / products."
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Analysis
by VulDB Data Team • 08/01/2023
The vulnerability identified as CVE-2019-9747 affects the tinysvcmdns library, a lightweight implementation of Multicast DNS protocol designed for embedded systems and network service discovery. This library serves as a minimal mDNS resolver and advertiser, commonly used in IoT devices, network appliances, and embedded systems where resource constraints necessitate compact implementations of network protocols. The specific issue lies within the packet parsing mechanism that handles compressed labels in mDNS queries, creating a critical security flaw that can be exploited to cause denial of service conditions.
The technical flaw manifests when the uncompress_nlabel function encounters mDNS packets containing circular references in compressed labels, where label pointers reference each other in a loop. This creates an infinite loop during packet parsing operations, causing the mDNS server process to hang indefinitely without proper termination or error handling. The vulnerability specifically targets the decompression logic that should resolve pointer references in mDNS labels, but fails to implement proper cycle detection or maximum iteration limits. This type of flaw falls under CWE-835, which describes the weakness of infinite loops without proper termination conditions, and represents a classic example of resource exhaustion through algorithmic complexity attacks.
The operational impact of this vulnerability extends beyond simple service disruption, as it can affect the availability of network services that depend on mDNS functionality. When exploited, maliciously crafted mDNS packets can cause network devices running tinysvcmdns to become unresponsive, potentially leading to complete network service outages. This is particularly concerning in embedded systems and IoT environments where such devices may be critical infrastructure components or may operate without human intervention. The vulnerability demonstrates how seemingly benign protocol parsing operations can become attack vectors when proper input validation and loop termination mechanisms are absent, aligning with ATT&CK technique T1499.004 for network denial of service attacks.
Mitigation strategies for this vulnerability should focus on immediate code-level fixes including implementing maximum iteration limits in label decompression routines, adding cycle detection mechanisms, and incorporating proper input validation for compressed label structures. Organizations using tinysvcmdns should consider migrating to actively maintained alternatives such as libmdns, avahi, or other modern mDNS implementations that have addressed similar parsing vulnerabilities. The advisory's recommendation against using this library for new projects underscores the importance of avoiding deprecated software with known security flaws, particularly in security-sensitive environments where maintaining up-to-date and secure network protocols is essential for overall system integrity. Additionally, network segmentation and monitoring solutions should be implemented to detect and mitigate potential exploitation attempts targeting this specific vulnerability pattern.