CVE-2020-27736 in Nucleus NET
Summary
by MITRE • 04/23/2021
A vulnerability has been identified in Nucleus 4 (All versions < V4.1.0), Nucleus NET (All versions), Nucleus RTOS (versions including affected DNS modules), Nucleus ReadyStart (All versions < V2017.02.3), Nucleus Source Code (versions including affected DNS modules), SIMOTICS CONNECT 400 (All versions < V0.5.0.0), VSTAR (versions including affected DNS modules). The DNS domain name label parsing functionality does not properly validate the null-terminated name in DNS-responses. The parsing of malformed responses could result in a read past the end of an allocated structure. An attacker with a privileged position in the network could leverage this vulnerability to cause a denial-of-service condition or leak the read memory.
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Analysis
by VulDB Data Team • 04/27/2021
This vulnerability resides within the Domain Name System parsing functionality of multiple Nucleus operating system variants and related software components including Nucleus 4, Nucleus NET, Nucleus RTOS, Nucleus ReadyStart, Nucleus Source Code, SIMOTICS CONNECT 400, and VSTAR. The flaw manifests in the DNS domain name label parsing mechanism where the system fails to properly validate null-terminated strings within DNS responses. This represents a classic buffer over-read condition that falls under CWE-125, where the parsing logic attempts to read memory beyond the boundaries of allocated structures. The vulnerability affects all versions of these components prior to their respective security patches, with Nucleus 4 requiring version 4.1.0 or higher, Nucleus ReadyStart requiring version 2017.02.3 or higher, and SIMOTICS CONNECT 400 requiring version 0.5.0.0 or higher to be protected.
The technical implementation of this vulnerability stems from improper validation of DNS response structures during the parsing of domain name labels. When a malformed DNS response is received, the parsing code does not adequately check bounds before accessing memory locations that may extend beyond the legitimate allocated buffer space. This occurs specifically in the handling of null-terminated strings within DNS name labels where the parser assumes proper termination without validating the actual structure of the received data. The vulnerability operates at the network protocol level where DNS responses are processed by embedded systems, making it particularly dangerous in industrial control environments where these systems are prevalent. The flaw allows for both denial-of-service conditions through system crashes or hangs, and information disclosure through memory leaks that could expose sensitive data from the system's memory space.
From an operational perspective, this vulnerability presents a significant risk to embedded systems and industrial environments where Nucleus-based software is deployed. The attack vector requires an attacker with a privileged network position, meaning they must be able to inject malicious DNS responses into the network traffic flow. This could occur through man-in-the-middle attacks, compromised network infrastructure, or DNS poisoning techniques that are commonly employed in advanced persistent threat campaigns. The impact of exploitation includes system instability leading to denial-of-service conditions that could disrupt critical operations, particularly in industrial control systems where availability is paramount. Additionally, the memory leak aspect could expose sensitive information including system configuration details, authentication credentials, or operational data that might be stored in the memory regions being accessed beyond their intended boundaries.
The mitigation strategy for this vulnerability involves upgrading all affected components to their patched versions as specified by the vendor. Organizations should prioritize updating Nucleus 4 to version 4.1.0 or higher, Nucleus ReadyStart to version 2017.02.3 or higher, and SIMOTICS CONNECT 400 to version 0.5.0.0 or higher. Network segmentation and monitoring should be implemented to detect anomalous DNS traffic patterns that might indicate attempted exploitation. Implementing DNS security measures such as DNSSEC validation can help prevent injection of malicious DNS responses. Additionally, network administrators should consider deploying intrusion detection systems that can monitor for DNS response anomalies and establish secure communication channels where possible. The vulnerability aligns with ATT&CK technique T1071.004 for application layer protocol tunneling and T1566 for credential access through network infrastructure compromise, making it a critical target for defensive measures in industrial control system security programs.