SSH Pre-Authentication Rekey State Bypass in MikroTik RouterOS

Description

RouterOS SSH enters the connection protocol after a client-requested rekey even though user authentication was never attempted, allowing an unauthenticated client to open a session channel and send an exec request. On affected builds the server dispatches the command, enabling unauthenticated creation, overwrite, and reconstruction of files in the RouterOS managed file namespace, including support files containing configuration and diagnostic data.This issue was fixed in versions: 6.49.21 (Long-term), 7.23.4 (Long-term) and 7.24.2 (Stable)

Also Affects

Downstream vendors/products affected by this vulnerability

References

• https://cert.pl/en/posts/2026/09/mikrotik-routeros-cve(third-party-advisory)
• https://cert.pl/en/posts/2026/09/vulnerabilities-in-mikrotik-routeros-actively-exploited/(technical-description)
• https://npratley.net/reversing-mikrotiks-silent-patch-the-routeros-7-23-4-fix-they-wouldnt-explain/(exploit)
• https://mikrotik.com/supportsec/september-2026-vulnerability/(vendor-advisory)
• https://forum.mikrotik.com/t/6-49-21-long-term-is-released/272802(release-notes)
• https://forum.mikrotik.com/t/7-23-4-long-term-is-released/272801(release-notes)
• https://forum.mikrotik.com/t/7-24-2-stable-is-released/272800(release-notes)

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