CVE-2026-67277
high CISA KEVMikroTik RouterOS Missing Authentication for Critical Function Vulnerability
Vendor / product: MikroTik — RouterOS
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)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H Required action (CISA)
Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
Affected products
Weakness classification (CWE)
Source: NVD / CISA. “NVD-CWE-Other” and “NVD-CWE-noinfo” mean NVD could not assign a specific weakness.
Mitigation & advisories
References
- https://cert.pl/en/posts/2026/09/mikrotik-routeros-cve cvd@cert.pl
- https://cert.pl/en/posts/2026/09/vulnerabilities-in-mikrotik-routeros-actively-exploited/ cvd@cert.pl
- https://forum.mikrotik.com/t/6-49-21-long-term-is-released/272802 cvd@cert.pl
- https://forum.mikrotik.com/t/7-23-4-long-term-is-released/272801 cvd@cert.pl
- https://forum.mikrotik.com/t/7-24-2-stable-is-released/272800 cvd@cert.pl
- https://mikrotik.com/supportsec/september-2026-vulnerability/ cvd@cert.pl
- https://npratley.net/reversing-mikrotiks-silent-patch-the-routeros-7-23-4-fix-they-wouldnt... cvd@cert.pl
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-67277 134c704f-9b21-4f2e-91b3-4a467353bcc0