CVE-2026-67277 — RouterOS accepts a "related" btest connection before the corresponding primary s

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 fr

01What is this vulnerability?

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…

02Affected products

No structured affected-product list available — see references below for vendor advisories.

03Active exploitation status

Yes — actively exploited. Added to the CISA KEV catalog on 2026-09-10. Ransomware use: Unknown.

04Recommended remediation

• Patch to a fixed version listed in the vendor advisory (see references below).
• Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
• Hunt historical logs for exploitation indicators — see Detection signatures below.

05Technical details

For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.

06Detection signatures

Open the Sigma generator with a pre-filled prompt for this CVE to draft a starting detection in your stack of choice:

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07Related CVEs

No directly-cited follow-up CVEs in the KB record for this advisory. The references list in section 09 carries the vendor cross-references.

08Timeline

• Published: 2026-09-05T20:17:18.120
• Last modified: 2026-09-11T12:52:29.533
• Added to CISA KEV: 2026-09-10

09References

• cert.pl — https://cert.pl/en/posts/2026/09/mikrotik-routeros-cve
• cert.pl — https://cert.pl/en/posts/2026/09/vulnerabilities-in-mikrotik-routeros-actively-e…
• forum.mikrotik.com — https://forum.mikrotik.com/t/6-49-21-long-term-is-released/272802
• forum.mikrotik.com — https://forum.mikrotik.com/t/7-23-4-long-term-is-released/272801
• forum.mikrotik.com — https://forum.mikrotik.com/t/7-24-2-stable-is-released/272800
• mikrotik.com — https://mikrotik.com/supportsec/september-2026-vulnerability/
• npratley.net — https://npratley.net/reversing-mikrotiks-silent-patch-the-routeros-7-23-4-fix-th…
• www.cisa.gov — https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-…