A critical vulnerability in the Siemens Reyrolle 7SR5 web interface permits unauthenticated attackers to bypass authentication by predicting session IDs, posing a high risk of unauthorized device access.

The device suffers from a flaw in session management where predictable session identifiers are exposed via the web interface. This allows an unauthenticated attacker to bypass authentication mechanisms and interact with critical device functions.

The ability for an unauthenticated attacker to gain full access to a critical power protection relay poses a severe threat to operational technology environments. Given the CVSS score of 9.8, this vulnerability could lead to unauthorized configuration changes, device manipulation, or disruption of industrial processes, potentially resulting in significant physical damage or operational downtime.

Immediate Action: Administrators must update the Siemens Reyrolle 7SR5 firmware to version V2.70 or later as specified in the official Siemens security advisory.

Proactive Monitoring: Security teams should monitor device access logs for unusual login patterns or multiple failed authentication attempts originating from unexpected IP addresses.

Compensating Controls: Restrict network access to the device web interface by placing it behind a secure gateway or firewall, ensuring only authorized management workstations can communicate with the device.

Public Exploit Available: No (exploit_available unknown).

Due to the critical nature of this vulnerability and the potential for complete loss of control over industrial hardware, immediate remediation is required. Organizations should prioritize patching all affected Reyrolle 7SR5 units to version V2.70 and audit network configurations to ensure these devices are not directly exposed to untrusted networks.