CVE-2020-6071 in libmicrodns
Summary
by MITRE
An exploitable denial-of-service vulnerability exists in the resource record-parsing functionality of Videolabs libmicrodns 0.1.0. When parsing compressed labels in mDNS messages, the compression pointer is followed without checking for recursion, leading to a denial of service. An attacker can send an mDNS message to trigger this vulnerability.
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Analysis
by VulDB Data Team • 05/05/2026
The vulnerability identified as CVE-2020-6071 represents a critical denial-of-service weakness within the Videolabs libmicrodns library version 0.1.0, specifically affecting the resource record parsing mechanism used in multicast dns implementations. This flaw resides in the library's handling of compressed labels within mDNS messages, where the software fails to validate recursive pointer references during decompression operations. The issue stems from insufficient input validation and lacks proper bounds checking mechanisms that would normally prevent infinite loops or stack exhaustion during recursive decompression processes. As a result, the library becomes susceptible to malformed mDNS packets that contain maliciously constructed compression pointers designed to create recursive references.
The technical exploitation of this vulnerability occurs when the libmicrodns library processes mDNS messages containing compressed labels with recursive pointers. During the decompression phase, the parser follows compression pointers without implementing recursion depth limits or cycle detection mechanisms. This allows an attacker to craft mDNS packets with circular or deeply nested compression references that cause the parser to enter infinite loops or consume excessive memory resources. The vulnerability specifically targets the decompression algorithm's pointer traversal logic, where each dereferenced pointer leads to another pointer without proper validation of previously visited locations or maximum recursion thresholds. This flaw aligns with CWE-674, which describes the issue of uncontrolled recursion in software systems, and represents a classic example of insufficient input validation leading to resource exhaustion.
The operational impact of this vulnerability extends beyond simple service disruption, as it affects any application or system that relies on libmicrodns for mDNS resolution services. Network devices, IoT systems, and applications implementing multicast dns functionality become vulnerable to remote denial-of-service attacks that can render them unusable until manual intervention occurs. The attack vector requires only the transmission of a specially crafted mDNS message to the target system, making it particularly dangerous in networked environments where mDNS traffic is common. Systems running affected software may experience complete service unavailability, memory exhaustion, or process termination, potentially affecting critical infrastructure components that depend on multicast dns for device discovery and service resolution. The vulnerability's exploitation does not require authentication or elevated privileges, making it accessible to any attacker with network access to the target system.
Mitigation strategies for CVE-2020-6071 should focus on immediate library updates to versions that implement proper recursion detection and depth limiting mechanisms. Organizations should prioritize patching affected systems and updating the libmicrodns library to versions that address the recursive pointer handling issue. Additionally, network-level defenses such as rate limiting for mDNS traffic and implementing firewall rules to restrict mDNS packet processing can provide temporary protection while patches are deployed. The implementation of input validation controls and bounds checking for compression pointer references should be enforced across all mDNS implementations. Security monitoring should include detection of anomalous mDNS traffic patterns that might indicate exploitation attempts, and system administrators should implement proper logging and alerting mechanisms to identify potential attacks targeting this vulnerability. This vulnerability demonstrates the importance of proper input validation and recursion handling in network protocol implementations, aligning with ATT&CK technique T1499.002 for network denial of service attacks and highlighting the need for robust defensive measures in protocol parsing components.