SSH session privilege manipulation via a crafted username in Mikrotik RouterOS

Description

RouterOS contains an argument-handling flaw in the SSH login path involving usernames that begin with a prohibited character, allowing for the trusted RouterOS policy mask to be changed, leading to privilege escalation. Exploitation requires an unauthenticated SSH session to reach the RouterOS login helper.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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