CVE-2026-62647 in Reyrolle 7SR5
Summary
by MITRE • 09/08/2026
A vulnerability has been identified in Reyrolle 7SR5 (All versions < V2.70). A random number generator is used to generate security-relevant values (such as session identifiers used for authentication purposes) that is not initialized with a True Random Number Generator (TRNG), resulting in a predictable sequence of generated values. This could allow an unauthenticated remote attacker to more easily predict the generated values and impersonate a legitimate authenticated user, potentially gaining unauthorized access to the device.
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Analysis
by VulDB Data Team • 09/08/2026
The Reyrolle 7SR5 series protection relays are critical components within industrial control systems and power grid infrastructure, responsible for monitoring electrical parameters and initiating protective actions such as circuit breaker tripping when faults occur. These devices rely heavily on secure communication protocols to ensure that configuration changes, status updates, and command executions originate from authorized personnel only. The identified vulnerability resides in the cryptographic implementation of session management mechanisms within firmware versions prior to V2.70. Specifically, the system utilizes a pseudo-random number generator for creating security-sensitive values, including session identifiers used during authentication processes. In secure software engineering practices, any value intended to prevent replay attacks or facilitate unique session tracking must be derived from a source with high entropy and unpredictability. The failure to initialize this random number generation process using a True Random Number Generator constitutes a fundamental flaw in the device's security architecture, as it violates the principle of non-deterministic state initialization required for robust cryptographic operations.
From a technical perspective, the core issue is that the pseudo-random number generator lacks proper seeding with entropy derived from physical phenomena or hardware-based random sources. Instead, it likely relies on deterministic algorithms initialized with predictable seeds such as system uptime, default constants, or low-entropy environmental variables common in embedded systems. This results in a sequence of generated session identifiers that are not only reproducible but also potentially guessable by an attacker who can observe previous interactions or analyze the algorithm's output patterns over time. An unauthenticated remote attacker capable of network access to the device can exploit this weakness by predicting valid session tokens. By generating these predictable values, the attacker can forge authentication requests that appear legitimate to the relay’s processing logic. This effectively bypasses the intended access control mechanisms, allowing the adversary to establish a authenticated session without possessing valid credentials or multi-factor authentication factors.
The operational impact of this vulnerability is severe due to the critical nature of the protected infrastructure. Once an attacker gains unauthorized access through predicted session identifiers, they can manipulate relay settings, disable protection functions for specific line segments, or trigger false trips that lead to unplanned power outages. In a broader context, such manipulation could be used as part of a larger cyber-physical attack against energy grids, potentially causing cascading failures, equipment damage due to lack of fault isolation, or economic losses from prolonged downtime. The ability to impersonate legitimate users also compromises the integrity and auditability of system logs, making it difficult for operators to detect intrusions or trace malicious activities back to their source. This directly undermines the confidentiality, integrity, and availability pillars of information security within industrial environments where reliability is paramount.
This vulnerability aligns with CWE-330: Use of Insufficiently Random Values, which describes flaws in random number generation that lead to predictable outputs suitable for cryptographic attacks. Furthermore, it maps to MITRE ATT&CK technique T1078: Valid Accounts, specifically the sub-technique of obtaining credentials through prediction or brute-force methods facilitated by weak randomness. The exploitation path resembles aspects of CWE-284: Improper Access Control, as the attacker bypasses authentication controls via session hijacking techniques enabled by the predictable identifiers. To mitigate this risk, operators must immediately upgrade Reyrolle 7SR5 devices to version V2.70 or later where the random number generator has been corrected to utilize a True Random Number Generator with proper entropy sources. Until patching is complete, network segmentation strategies should be enforced to restrict direct remote access to these devices from untrusted networks. Additionally, implementing strict firewall rules that limit management interfaces to specific administrative IP addresses and enabling multi-factor authentication where supported can provide compensating controls against exploitation of this flaw. Regular security audits and penetration testing focused on cryptographic implementations are recommended to identify similar weaknesses in other industrial control system components.