Auth bypass in Mikrotik Routeros
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)
Vulnerability class: Broken Authentication
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.2 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H.
EPSS exploit prediction
EPSS: 0.016 (75.0th percentile), scored .
Low probability of exploitation in the next 30 days, but still tracked. 75th percentile — 75.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.009 · newest: 0.016 · change: +0.007
Affected products
Weakness classification (CWE)
CISA KEV (Known Exploited Vulnerabilities)
This CVE is on the CISA KEV catalog, added on . CISA KEV inclusion means CISA has confirmed in-the-wild exploitation; US federal agencies are required to remediate within a published due date.
BOD 22-01 due date: .
Required action: 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.
References
- cert.pl/en/posts/2026/09/mikrotik-routeros-cve (Third Party Advisory, third-party-advisory)
- cert.pl/en/posts/2026/09/vulnerabilities-in-mikrotik-routeros-actively-exploite… (technical-description, Third Party Advisory, Mitigation)
- forum.mikrotik.com/t/6-49-21-long-term-is-released/272802 (release-notes, Release Notes)
- forum.mikrotik.com/t/7-23-4-long-term-is-released/272801 (release-notes, Release Notes)
- forum.mikrotik.com/t/7-24-2-stable-is-released/272800 (release-notes, Release Notes)
- mikrotik.com/supportsec/september-2026-vulnerability/ (vendor-advisory, Vendor Advisory)
- npratley.net/reversing-mikrotiks-silent-patch-the-routeros-7-23-4-fix-they-woul… (Exploit, Third Party Advisory, exploit)
- 134c704f-9b21-4f2e-91b3-4a467353bcc0 (US Government Resource)
Frequently asked questions
- What is CVE-2026-67277?
- CVE-2026-67277 is a high-severity vulnerability in Mikrotik Routeros, classified under Missing Authentication for Critical Function. CVSS score: 8.2/10. Published 2026-09-05.
- How severe is CVE-2026-67277?
- High severity. CVSS v3 base score is 8.2 out of 10.
- Is CVE-2026-67277 known to be exploited?
- Yes. CVE-2026-67277 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2026-09-10), indicating it is being actively exploited.