CVE-2026-67277
MikroTik RouterOS Missing Authentication for Critical Function Vulnerability
Does this matter?
Known to be exploited in the wild (CISA KEV, CISA remediation deadline 13 September 2026). Treat as an emergency change: patch or isolate now, then hunt for prior compromise.
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)
- CVSS 4.0
- 8.8 HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 0.86% probability · 56th percentile
- CISA KEV
- Listed 10 September 2026 · due 13 September 2026
- Weakness
- CWE-306
- Affected
- mikrotik/routeros
- Source
- cvd@cert.pl
CISA notes
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. https://mikrotik.com/supportsec/september-2026-vulnerability/ ; BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk ; Forensics Triage Requirements: https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk ; https://nvd.nist.gov/vuln/detail/CVE-2026-67277
References
- https://cert.pl/en/posts/2026/09/mikrotik-routeros-cveThird Party Advisory
- https://cert.pl/en/posts/2026/09/vulnerabilities-in-mikrotik-routeros-actively-exploited/Mitigation, Third Party Advisory
- https://forum.mikrotik.com/t/6-49-21-long-term-is-released/272802Release Notes
- https://forum.mikrotik.com/t/7-23-4-long-term-is-released/272801Release Notes
- https://forum.mikrotik.com/t/7-24-2-stable-is-released/272800Release Notes
- https://mikrotik.com/supportsec/september-2026-vulnerability/Vendor Advisory
- https://npratley.net/reversing-mikrotiks-silent-patch-the-routeros-7-23-4-fix-they-wouldnt-explain/Exploit, Third Party Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-67277US Government Resource
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.