CVE-2026-67279mediumunder attackCWE-841

CVE-2026-67279: medium-severity vulnerability in Mikrotik RouterOS

SSH Pre-Authentication Rekey State Bypass in MikroTik RouterOS

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63Vexday Risk Score

Prioritize patching. It under exploitation confirmed by CISA, has an official Brazilian government alert and has a public proof of concept.

ssvc Actcvss 6.9epss 2.3%
from disclosure to weapon20 days
Published on NVDSep 5
1st PoC+20d
CISA KEV+20d
Official alert in Brazil

Brazil's federal government published an alert, recommendation or bulletin that cites this vulnerability.

Source: CTIR Gov (GSI) and CISC Gov.br, under the CC BY-ND 3.0 license.
Action required by CISAfederal deadline: 2026-09-28

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.

In short

MikroTik RouterOS SSH allows unauthenticated users to execute commands and manipulate files by triggering a rekey operation before completing login. An attacker can create, modify, or overwrite configuration files without providing valid credentials.

Technical detail

CVE-2026-67279 is a pre-authentication bypass in SSH protocol handling where RouterOS incorrectly transitions to the connection protocol state upon client-initiated rekey without enforcing user authentication (CWE-841: Improper Synchronization). An unauthenticated attacker can open session channels and execute arbitrary commands, enabling unauthorized file creation and modification in the RouterOS filesystem, including sensitive configuration and diagnostic data.

Summary generated and translated by AI from the official description.
RouterOS SSH enters the connection protocol after a client-requested rekey even though user authentication was never attempted, allowing an unauthenticated client to open a session channel and send an exec request. On affected builds the server dispatches the command, enabling unauthenticated creation, overwrite, and reconstruction of files in the RouterOS managed file namespace, including support files containing configuration and diagnostic data.This issue was fixed in versions: 6.49.21 (Long-term), 7.23.4 (Long-term) and 7.24.2 (Stable)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
Affected products
Mikrotik · RouterOS
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