CVE-2026-67277highunder attackCWE-306

CVE-2026-67277: high-severity vulnerability in Mikrotik RouterOS

Kernel memory disclosure and denial of service in MikroTik RouterOS btest service

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71Vexday 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 8.8epss 1.6%
from disclosure to weapon
Published on NVDSep 5
CISA KEV+5d
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: 2026-09-13

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

RouterOS allows unauthenticated users to connect to a testing service without proper authentication, leaking sensitive data from the system's memory and potentially crashing the router. This happens because the router accepts connections before verifying the user's identity.

Technical detail

CVE-2026-67277 exploits improper access control (CWE-306) in RouterOS btest service, allowing unauthenticated clients to initiate UDP test sessions and trigger kernel memory disclosure via uninitialized buffer transmission. An integer underflow in packet-size handling causes excessive fragmentation and kernel crash; requires network access but no prior authentication.

Summary generated and translated by AI from the official 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/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N
Affected products
Mikrotik · RouterOS
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