CVE-2026-67277: mikrotik routeros

CVSS 8.8 (high) · listed as exploited by CISA since 2026-09-10 · published 2026-09-05

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 (NVD): mikrotik routeros

Fixed in (NVD): 6.49.21, 7.23.4, 7.24.2

Weakness: CWE-306

Source: NVD CVE-2026-67277

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/
• 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

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