CVE-2026-67277
Act now ● On CISA KEV — actively exploited
Actively exploited — on the CISA KEV list.
CVSS base
8.2
HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
EPSS — probability of exploitation (30 days)
0.9%
57.2th percentile
CISA KEV
Listed
Added 2026-09-10 · patch by 2026-09-13
Weakness / dates
CWE-306
Published 2026-09-05 · modified 2026-09-11
Description
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
References
- https://cert.pl/en/posts/2026/09/mikrotik-routeros-cve
- https://cert.pl/en/posts/2026/09/vulnerabilities-in-mikrotik-routeros-actively-exploited/
- https://forum.mikrotik.com/t/6-49-21-long-term-is-released/272802
- https://forum.mikrotik.com/t/7-23-4-long-term-is-released/272801
- https://forum.mikrotik.com/t/7-24-2-stable-is-released/272800
- https://mikrotik.com/supportsec/september-2026-vulnerability/
- exploit https://npratley.net/reversing-mikrotiks-silent-patch-the-routeros-7-23-4-fix-they-wouldnt-explain/
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-67277