---
title: "CVE-2026-67277: MikroTik RouterOS Missing Authentication for Critical Function Vulnerability"
url: https://erroneo.us/security/cve/CVE-2026-67277/
description: "CVE-2026-67277 (MikroTik RouterOS): Exploited in the wild (CISA KEV). RouterOS accepts a \"related\" btest connection before the corresponding primary session…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-09-05
date_modified: 2026-10-06
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-67277"
kev: true
cvss: 8.8
epss: 0.0156
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-67277: MikroTik RouterOS Missing Authentication for Critical Function Vulnerability

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Yes, if you run MikroTik RouterOS. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-09-10, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-09-13 ; treat that as the outer limit, not the target.
- EPSS 1.6% , percentile 75: FIRST’s model estimates a 1.6% chance of exploitation activity in the next 30 days, higher than 75% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Editorial verdict: Act now. MikroTrick: Exploited MikroTik RouterOS SSH Takeover Chain — If you run MikroTik routers, upgrade them now and check for an 'ops' admin account; an unauthenticated SSH chain to full admin was exploited a day before patches shipped.

## What it is

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)

## Affected products (CVE record)

- Mikrotik RouterOS: 7.24 < 7.24.2, 7.0.0 < 7.23.4, 6.0.0 < 6.49.21

## Severity

- CERT-PL CVSS 4.0: 8.8 `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`

## Exploitation

- CISA KEV: added 2026-09-10; federal due date 2026-09-13. Known ransomware use: Unknown.
- CISA 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.
- CISA SSVC assessment: exploitation active , automatable yes , technical impact partial .
- FIRST EPSS (model of 2026-10-21): 1.56% probability of exploitation activity in the next 30 days; percentile 75.

## Sources

- [mikrotik.com](https://mikrotik.com/supportsec/september-2026-vulnerability/)
- [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)
- [CVE.org record CVE-2026-67277](https://www.cve.org/CVERecord?id=CVE-2026-67277)
- [NVD entry CVE-2026-67277](https://nvd.nist.gov/vuln/detail/CVE-2026-67277)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-67277)
- [Listed in CISA KEV notes (cisa.gov)](https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk)
- [Listed in CISA KEV notes (cisa.gov)](https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk)
- [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-exploited/)
- [npratley.net](https://npratley.net/reversing-mikrotiks-silent-patch-the-routeros-7-23-4-fix-they-wouldnt-explain/)

---
Source page: https://erroneo.us/security/cve/CVE-2026-67277/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt