CVE-2019-9748 in tinysvcmdns
Summary
by MITRE
In tinysvcmdns through 2018-01-16, an mDNS server processing a crafted packet can perform arbitrary data read operations up to 16383 bytes from the start of the buffer. This can lead to a segmentation fault in uncompress_nlabel in mdns.c and a crash of the server (depending on the memory protection of the CPU and the operating system), or disclosure of memory content via error messages or a server response. 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-2019-9748 affects the tinysvcmdns library, a lightweight implementation of the Multicast DNS protocol designed for embedded systems and small applications. This mDNS server implementation processes network packets containing DNS queries and responses, but suffers from a critical buffer over-read condition that can be exploited by malicious actors to gain unauthorized access to memory contents or cause system crashes. The vulnerability stems from improper handling of DNS label compression during packet parsing, specifically in the uncompress_nlabel function within the mdns.c source file. The flaw allows an attacker to craft specially formatted DNS packets that trigger memory access beyond the intended buffer boundaries, potentially reading up to 16383 bytes of adjacent memory content.
The technical exploitation of this vulnerability occurs when the mDNS server receives a malformed packet containing crafted DNS labels that exceed the expected buffer limits during decompression operations. According to CWE-129, this represents an implementation of an insufficient bounds check, specifically a buffer overflow condition that manifests as an out-of-bounds read rather than a write operation. The vulnerability is categorized under the ATT&CK technique T1059.007 for Command and Scripting Interpreter: Python, as attackers could potentially leverage the memory disclosure to discover system information or application state that could aid in further exploitation. When the buffer over-read occurs, the system may experience segmentation faults in the uncompress_nlabel function, leading to server crashes and denial of service conditions that can impact legitimate network services relying on mDNS resolution.
The operational impact of this vulnerability extends beyond simple service disruption to include potential information disclosure that could expose sensitive data from the server's memory space. Attackers who successfully exploit this vulnerability may gain access to memory segments containing application state, configuration data, or even cryptographic keys that are stored in the server's address space. The severity of the impact depends on the memory protection mechanisms of the target system, including features like address space layout randomization and data execution prevention that may mitigate some exploitation vectors. This vulnerability is particularly concerning in embedded environments where tinysvcmdns is commonly deployed, as these systems often lack robust security mitigations and may be used in critical infrastructure applications where the exposure of memory contents could lead to more severe consequences.
The recommended mitigation strategies for this vulnerability include immediate discontinuation of using the tinysvcmdns library in production environments, as the project has been unmaintained since 2013 and contains known security issues. Organizations should migrate to actively maintained DNS resolution libraries such as libmdns or other modern implementations that have proper bounds checking and memory protection mechanisms. System administrators should implement network segmentation and access controls to limit exposure to potentially malicious DNS traffic, while also monitoring for unusual DNS packet patterns that might indicate exploitation attempts. The vulnerability serves as a prime example of why organizations should avoid using unmaintained software libraries, particularly in security-critical applications where memory safety is paramount. Additionally, implementing proper input validation and bounds checking in all network-facing applications can help prevent similar vulnerabilities from being exploited in other software components.