What is CVE-2026-67277?
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)
Timeline
- 2026-09-05Published to the U.S. National Vulnerability Database (NVD)
- 2026-09-10Added to the CISA Known Exploited Vulnerabilities (KEV) catalog
- 2026-09-11NVD record last updated
- 2026-09-13CISA federal remediation deadline (BOD 22-01)
CISA Known Exploited Vulnerability
MikroTik RouterOS Missing Authentication for Critical Function Vulnerability
Affected product
MikroTik RouterOS
Remediation Steps
- Apply the vendor patch for Mikrotik products
- Check CISA's Known Exploited Vulnerabilities catalog for current advisories
- Review system logs for unauthorized access or configuration changes
- Restrict network access to affected Mikrotik devices from untrusted networks
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://nvd.nist.gov/vuln/detail/CVE-2026-67277
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog
Referenced in our briefings & reports
- Vulnerability Priority Report – Week 1 of September 2026 (September 7 – 13)
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🤖 This CVE page is generated by defend.network from NVD, CISA KEV, EPSS, and our verified daily briefings. Severity and exploitation data come from official sources; always verify remediation steps against the official vendor advisory before acting in production.