Vulnerability details

RouterOS accepts a "related" btest connection before the corresponding primary session has completed authentication. An unauthenticated client can use this state to start an IPv4 UDP test. With "random-data=false", the sender transmits an uninitialized tail from a kernel packet buffer. A separate unchecked, inverted packet-size interval causes unsigned integer underflow, anomalously large fragmented output, and can restart the RouterOS kernel. This issue was fixed in versions: 6.49.21 (Long-term), 7.23.4 (Long-term) and 7.24.2 (Stable)

• 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
• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-67277 government-resource