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)
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (9.0): severity, escalated by confirmed exploitation. This CVE's 9.0 is the CISA KEV floor for confirmed exploitation, not an impact rating: its impact severity (EG Severity) is CVSS 8.2 HIGH.
- EG Severity
- 8.2 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 1.6% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-12). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- CISA KEV and ENISA EU KEV (Source: ENISA EUVD) and EG-KEV Tier 1 (exploited in the wild)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Attend at medium mission impactAttend at low or medium mission impact; Act at high (mission-essential systems).CISA BOD 26-04: 3 days if the affected system is publicly exposed; 14 days if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
ENISA EU KEV: listed September 5, 2026, reported by CERT.PL.
Source: ENISA EUVD (EU Known Exploited Vulnerabilities catalogue), reproduced with acknowledgement. How a listing moves the EG score
SSVC (CISA's decision table, applied by EchelonGraph)Attend at low or medium mission impact; Act at high (mission-essential systems).
The CVE record names the fixed release. Apply it sooner than your standard update timelines at low or medium mission impact and as soon as possible at high.
Exploitation active (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)3 days if the affected system is publicly exposed; 14 days if it is not.
The score's inputs: In CISA KEV yes (CISA's KEV catalog) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it
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.”
Quoted verbatim from CISA's Known Exploited Vulnerabilities catalog. CISA directs it at US federal civilian executive branch agencies under Binding Operational Directive (BOD) 26-04, which replaced BOD 22-01 on 10 June 2026; it is not EchelonGraph's advice. CISA's notes: https://mikrotik.com/supportsec/september-2026-vulnerability/ · https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk · https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk · https://nvd.nist.gov/vuln/detail/CVE-2026-67277