CVE-2026-67277

MikroTik RouterOS Missing Authentication for Critical Function Vulnerability

Actively exploited (CISA KEV) High 8.2 CVSS 3.1

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)

Description as published by the source, in English.

Key facts

Published: 2026-09-05
Last modified: 2026-09-11
Assigned by: cvd@cert.pl
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
Scored by: nvd@nist.gov (NVD Primary)
Fix available: Not registered in the sources

Actively exploited

CISA added this vulnerability to the Known Exploited Vulnerabilities catalogue on 2026-09-10, with a remediation deadline of 2026-09-13 for US federal agencies.

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.

Affected products

Vendor	Product	Versions	Status
Mikrotik	Routeros	≥ 6.0, < 6.49.21	Affected
Mikrotik	Routeros	≥ 7.0, < 7.23.4	Affected
Mikrotik	Routeros	≥ 7.24, < 7.24.2	Affected

Weakness type

CWE-306: Missing Authentication for Critical Function
The product does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources.

References

https://cert.pl/en/posts/2026/09/mikrotik-routeros-cve Third 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/272802 Release Notes
https://forum.mikrotik.com/t/7-23-4-long-term-is-released/272801 Release Notes
https://forum.mikrotik.com/t/7-24-2-stable-is-released/272800 Release Notes
https://mikrotik.com/supportsec/september-2026-vulnerability/ Vendor Advisory
https://npratley.net/reversing-mikrotiks-silent-patch-the-routeros-7-23-4-fix-they-wouldn… Exploit, Third Party Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-67277 US Government Resource

Related at Berigo

Articles

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CERT Polska has disclosed six vulnerabilities in MikroTik RouterOS and confirms that a chain of two SSH flaws, dubbed MikroTrick, is used in attacks …
CISA issues seven new ICS advisories, critical flaw in Siemens building automation Same product 2026-07-28
Seven new advisories cover Siemens, MikroTik, igloohome and ABB. The most severe is a 9.8-rated vulnerability in the Desigo CC building automation pl…

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Sources and freshness

CVE

What it is: A reference number naming one specific vulnerability, for example CVE-2024-9474.
What it tells you: Which vulnerability we are talking about, and in which product.
What it does NOT tell you: Nothing about how serious it is, whether anyone is exploiting it, or whether it concerns you.
Why it matters: Without a shared number, vendor, authority and tooling cannot discuss the same flaw.
Used with the others: The number is the key. NVD, KEV and EPSS all describe the same CVE.

NVD CWE CISA KEV EPSS

How to read this together

No single value should be used on its own. A high CVSS score does not mean a vulnerability is being exploited, and a low one does not mean it is harmless. The four sources answer four different questions.

CVE names the specific vulnerability.
NVD adds severity and technical detail about it.
CWE describes the type of mistake behind it.
CISA KEV shows that it is already being exploited.
EPSS estimates how likely exploitation is soon.

The order that decides what is urgent

Do you actually have the product?
Is the version you run affected?
Is it listed in CISA KEV?
Does it have a high EPSS score?
Is the system reachable from the internet or from others?
How important is the system to the business?
Are there compensating controls already in place?

The first two questions are not about the vulnerability at all. They are about you, and they remove most of the list before you start.

A short example

Fix this week

CVSS 6,5 (medium)

In CISA KEV: yes
EPSS: 94 per cent
A firewall facing the internet

Can be scheduled

CVSS 9,8 (critical)

In CISA KEV: no
EPSS: 0,04 per cent
A test server with no internet access

Sorted by CVSS alone, the one on the right comes first. It is the more serious flaw in theory. But the one on the left is being used against real organisations right now, and it sits where an attacker can reach it. That is the one to fix first.

The critical one still has to be fixed. It just does not have to be fixed today.

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Scores and vectors are shown as published by the sources. The ordering of results is Berigo's own editorial assessment, described on the search page, and is not NVD data. An empty result never means a system is safe.