CVE-2026-67277

high

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)

References

https://mikrotik.com/supportsec/september-2026-vulnerability/

https://npratley.net/reversing-mikrotiks-silent-patch-the-routeros-7-23-4-fix-they-wouldnt-explain/

https://www.securityweek.com/mikrotik-patches-critical-flaws-chained-to-hack-routers/

https://www.helpnetsecurity.com/2026/09/07/mikrotik-routeros-ssh-vulnerabilities-exploited/

https://www.bleepingcomputer.com/news/security/hackers-exploit-new-mikrotik-routeros-flaws-to-hijack-routers/

https://forum.mikrotik.com/t/7-24-2-stable-is-released/272800

https://forum.mikrotik.com/t/7-23-4-long-term-is-released/272801

https://forum.mikrotik.com/t/6-49-21-long-term-is-released/272802

https://cert.pl/en/posts/2026/09/vulnerabilities-in-mikrotik-routeros-actively-exploited/

https://cert.pl/en/posts/2026/09/mikrotik-routeros-cve

Details

Source: Mitre, NVD

Published: 2026-09-05

Updated: 2026-09-09

Risk Information

CVSS v2

Base Score: 7.8

Vector: CVSS2#AV:N/AC:L/Au:N/C:N/I:N/A:C

Severity: High

CVSS v3

Base Score: 9.1

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

Severity: Critical

CVSS v4

Base Score: 8.8

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N

Severity: High

EPSS

EPSS: 0.00435