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CVE-2026-62645 – Authentication Bypass via Session ID Prediction – Siemens Reyrolle 7SR5 (all versio

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Summary

CVE-2026-62645 is a critical authentication bypass vulnerability affecting Siemens Reyrolle 7SR5 protection relays. The web interface of affected devices exposes information that allows an attacker to calculate current and past session ID numbers, enabling unauthorized access without valid credentials. The flaw carries a CVSS v3.1 base score of 9.8 (Critical) and is remotely exploitable over the network with no privileges or user interaction required.

Technical details

  • Root cause: The device’s web interface leaks information that allows an attacker to derive (calculate) valid session ID values, classified as CWE-306 (Missing Authentication for Critical Function).
  • Trigger condition: An attacker who can reach the device’s web management interface can compute current or previously issued session IDs from exposed data, without needing to guess credentials.
  • Attack vector: Network-based (AV:N), low attack complexity, no privileges required, no user interaction — the vulnerability can be exploited remotely by any actor with network access to the exposed web interface.
  • Impact: Successful exploitation grants an attacker a valid authenticated session, resulting in full compromise of confidentiality, integrity, and availability of the device — effectively an authentication bypass that could allow unauthorized monitoring or manipulation of protection relay functions.
  • This flaw was disclosed alongside several related vulnerabilities (including weak session token generation and insufficient randomness in session ID generation) in the same Siemens advisory, which together compound the risk of session hijacking on this platform.

Affected software

  • Siemens Reyrolle 7SR5 — all versions prior to V2.70

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • CVSS v3.1 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  • (Siemens also rates this CVE 9.3 under CVSS v4.0)

Mitigation and recommended actions

  • Immediate: Update all Reyrolle 7SR5 devices to firmware version V2.70 or later, which resolves this vulnerability.
  • If immediate patching is not possible:
    • Restrict network access to the device’s web interface to trusted management networks only.
    • Place Reyrolle 7SR5 devices behind firewalls and segment them from untrusted or general corporate/IT networks.
    • Use VPNs or other secure remote-access mechanisms when access to the device’s web interface is required from outside a trusted network.
    • Follow Siemens’ operational guidelines for industrial security when deploying these devices in production environments.

References

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