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

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• 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)

CISA’s summary

MikroTik RouterOS contains a missing authentication for critical function vulnerability which allows kernel memory disclosure and denial of service in the btest service.

Weakness type: CWE-306.

Product: MikroTik RouterOS · Assigned by: CERT-PL · Published: 2026-09-05

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• 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.

Timeline

• 2026-09-03 — erroneo.us brief: MikroTrick: Exploited MikroTik RouterOS SSH Takeover Chain
• 2026-09-05 — CVE record published by CERT-PL
• 2026-09-10 — Added to CISA’s Known Exploited Vulnerabilities catalog
• 2026-09-11 — CVE record last updated
• 2026-09-13 — CISA remediation deadline for US federal agencies

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. mikrotik.com mikrotik.com
2. forum.mikrotik.com forum.mikrotik.com
3. forum.mikrotik.com forum.mikrotik.com
4. forum.mikrotik.com forum.mikrotik.com

Vulnerability records

1. CVE.org record CVE-2026-67277 cve.org
2. NVD entry CVE-2026-67277 nvd.nist.gov

Government

1. CISA Known Exploited Vulnerabilities catalog entry cisa.gov
2. Listed in CISA KEV notes (cisa.gov) cisa.gov
3. Listed in CISA KEV notes (cisa.gov) cisa.gov

Other references from the CVE record and advisory

1. cert.pl cert.pl
2. cert.pl cert.pl
3. npratley.net npratley.net

All exploited MikroTik vulnerabilities · Today’s Security Digest