CVE-2020-27738 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 record decompression functionality does not properly validate the pointer offset values. The parsing of malformed responses could result in a read access 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.
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Analysis
by VulDB Data Team • 04/27/2021
This vulnerability exists within multiple Nucleus embedded operating system components including Nucleus 4, Nucleus NET, Nucleus RTOS, Nucleus ReadyStart, Nucleus Source Code, SIMOTICS CONNECT 400, and VSTAR products. The flaw resides in the DNS domain name record decompression functionality where pointer offset values are not properly validated during parsing operations. This represents a classic implementation error that falls under CWE-129 Input Validation and CWE-787 Out-of-bounds Write, specifically manifesting as improper validation of pointer offsets in DNS response processing. The vulnerability affects all versions of these products prior to the specified patches, creating a widespread exposure across embedded systems that rely on DNS resolution for network communication.
The technical execution of this vulnerability occurs when malformed DNS responses are processed by the affected systems. During DNS decompression, the system attempts to follow pointer references within the DNS packet structure without adequate validation of the offset values. When an attacker crafts a malicious DNS response containing invalid pointer offsets, the decompression routine can attempt to read memory locations beyond the allocated buffer boundaries. This leads to a buffer over-read condition that can cause system instability and ultimately result in denial-of-service scenarios. The vulnerability is particularly dangerous because it requires only a privileged network position to exploit, making it accessible to attackers who can inject malicious DNS responses into the network traffic.
The operational impact of this vulnerability extends beyond simple denial-of-service conditions as it can compromise the availability and reliability of embedded systems that depend on DNS resolution. In industrial control systems, medical devices, and other critical infrastructure applications, such a vulnerability could lead to system outages that affect operational continuity. The affected products span various embedded environments where DNS resolution is critical for system functionality, including network connectivity, remote management, and application communication. The vulnerability's presence across multiple Nucleus product lines indicates a fundamental flaw in the DNS processing implementation that requires immediate attention.
Mitigation strategies should focus on implementing proper pointer validation during DNS decompression operations, which aligns with ATT&CK technique T1071.004 Application Layer Protocol: DNS. Organizations should upgrade to the patched versions of affected Nucleus products, specifically targeting Nucleus 4 version 4.1.0 and later, Nucleus ReadyStart version 2017.02.3 and later, and SIMOTICS CONNECT 400 version 0.5.0.0 and later. Additionally, network segmentation and DNS filtering mechanisms should be implemented to reduce the attack surface and prevent malicious DNS responses from reaching vulnerable systems. The fix should include bounds checking for pointer offset values, proper validation of DNS packet structures, and implementation of defensive programming practices to prevent out-of-bounds memory access. Regular security assessments and network monitoring should be conducted to identify and remediate similar vulnerabilities in embedded systems across the organization's infrastructure.