CVE-2026-67277: MikroTik RouterOS Missing Authentication for Critical Function Vulnerability

High severity, CVSS 8.2. Actively exploited: in CISA KEV since 2026-09-10. EPSS: 1.6% chance of exploitation in the next 30 days.

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)

Affected products

• MikroTik RouterOS: from 6.0, before 6.49.21 (fixed in 6.49.21); from 7.0, before 7.23.4 (fixed in 7.23.4); from 7.24, before 7.24.2 (fixed in 7.24.2)

Published 2026-09-05. Last modified 2026-09-11.