CVE-2020-9307 in OS2
Summary
by MITRE • 02/12/2021
Hirschmann OS2, RSP, and RSPE devices before HiOS 08.3.00 allow a denial of service. An unauthenticated, adjacent attacker can cause an infinite loop on one of the HSR ring ports of the device. This effectively breaks the redundancy of the HSR ring. If the attacker can perform the same attack on a second device, the ring is broken into two parts (thus disrupting communication between devices in the different parts).
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Analysis
by VulDB Data Team • 02/28/2021
The vulnerability identified as CVE-2020-9307 affects Hirschmann OS2, RSP, and RSPE network devices running firmware versions prior to HiOS 08.3.00. This represents a critical denial of service weakness that specifically targets the High Availability Ethernet Redundancy (HSR) protocol implementation within these industrial networking devices. The flaw exists in the handling of HSR ring port operations and creates a condition where an attacker can induce an infinite loop within the device's processing logic, fundamentally compromising the redundant network architecture that these devices are designed to provide.
The technical exploitation of this vulnerability requires an attacker to be physically adjacent to the target device, eliminating the need for authentication while maintaining network access. This adjacency requirement aligns with attack patterns classified under the MITRE ATT&CK framework's Initial Access phase, specifically targeting network infrastructure components. The vulnerability manifests as an infinite loop on one of the HSR ring ports, which causes the device to become unresponsive to normal network traffic while maintaining its physical presence on the network. The flaw operates at the protocol level where the device fails to properly handle malformed or maliciously crafted HSR ring messages, leading to resource exhaustion and system instability.
The operational impact of this vulnerability extends beyond simple service disruption, as it fundamentally undermines the redundancy mechanisms that industrial networks rely upon for high availability. When an infinite loop occurs on a single HSR ring port, the device cannot properly maintain its role in the redundant ring topology, effectively breaking the intended fault tolerance. If an attacker successfully targets multiple devices within the same HSR ring, the network can be partitioned into separate segments, completely disrupting communication between devices in different parts of the network. This scenario creates a cascading failure effect that can bring entire industrial control systems to a halt, particularly in environments where network redundancy is critical for operational continuity.
This vulnerability maps directly to CWE-835, which describes the weakness of an infinite loop or infinite recursion in software implementations. The flaw represents a classic example of improper input validation and resource management where the device fails to properly validate the integrity of HSR protocol messages before processing them. The attack vector demonstrates how industrial network devices can be compromised through physical proximity attacks, highlighting the importance of physical security controls in addition to traditional network security measures. Organizations should implement immediate mitigations including firmware updates to HiOS 08.3.00 or later versions, network segmentation to isolate affected devices, and monitoring for unusual network behavior that might indicate exploitation attempts. The vulnerability also underscores the need for comprehensive security assessments of industrial control systems, as traditional network security approaches may not adequately protect against physical proximity attacks targeting network infrastructure components.