CVE-2025-56301 is a vulnerability discovered in the Chipsalliance Rocket-Chip processor, specifically in the Control and Status Register (CSR) logic that manages exception handling and privilege state transitions. The flaw arises from a defective interaction between the exception handling mechanism and the MRET (Machine-mode Return from Exception) instruction. Normally, MRET is used to return from an exception by restoring the previous privilege state and program counter. However, if an exception is triggered during the execution of MRET in machine mode without an active exception state, both the exception handling logic and the MRET return logic activate simultaneously. This simultaneous activation causes conflicting updates to the CSR registers, resulting in faulty trap behavior and triggering an Instruction Access Fault. The vulnerability can corrupt the processor's exception handling flow and privilege state transitions, potentially causing system instability or denial of service. The CVSS v3.1 base score is 7.5 (high), reflecting its network attack vector, low attack complexity, no privileges required, no user interaction, unchanged scope, no confidentiality or integrity impact, but high impact on availability. No patches or exploits are currently available, but the flaw is significant for systems relying on Rocket-Chip processors, commonly used in embedded and specialized computing environments.

The primary impact of CVE-2025-56301 is on system availability due to the potential for denial of service caused by corrupted exception handling and privilege state transitions. For European organizations, especially those deploying Rocket-Chip-based embedded systems in critical infrastructure, industrial control, telecommunications, or IoT devices, this vulnerability could lead to unexpected system crashes or reboots. Although confidentiality and integrity are not directly affected, the disruption of exception handling could indirectly impair system reliability and safety. Given the network attack vector and no requirement for privileges or user interaction, attackers could remotely trigger this fault, increasing risk in exposed environments. The lack of known exploits in the wild reduces immediate threat but does not diminish the urgency for mitigation. Organizations relying on Rocket-Chip designs for critical applications should assess their exposure and prepare for patch deployment to avoid operational disruptions.

Since no official patches are currently available, European organizations should implement the following specific mitigations: 1) Conduct an inventory to identify all systems using the Chipsalliance Rocket-Chip processor, focusing on embedded and specialized devices. 2) Isolate vulnerable devices from untrusted networks to reduce exposure to remote exploitation. 3) Implement strict network segmentation and firewall rules to limit access to devices running Rocket-Chip processors. 4) Monitor system logs and exception handling events for anomalies indicative of corrupted trap behavior or unexpected Instruction Access Faults. 5) Engage with hardware vendors and Chipsalliance for updates or firmware patches addressing this vulnerability. 6) For new deployments, consider alternative processor designs until the vulnerability is resolved. 7) Develop incident response plans specifically addressing potential denial of service scenarios caused by this flaw. 8) Apply hardware-level mitigations if available, such as disabling or restricting MRET execution contexts where feasible. These targeted actions go beyond generic advice by focusing on network isolation, monitoring, and vendor engagement specific to the Rocket-Chip environment.