CVE-2026-67277
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)
At a glance
- Exploitability
- Can be exploited over the network without logging in. High risk of service disruption.
- In the wild
- CISA lists this as exploited in real attacks. Treat as urgent.
- Fix
- A patch, advisory or fixed version is referenced. Upgrade or apply it.
Timeline
- ReservedThe CVE id was reserved by its CNA
- PublishedDisclosed publicly on CVE.org and NVD
- 2026-09-10 Exploited in the wildAdded to CISA's Known Exploited Vulnerabilities list
- Last updatedMost recent change to the record
- 2026-09-13 Remediation deadlineCISA's due date for federal agencies to fix it
Why it ranks here
- Exploited in the wild: yes, CISA lists it. This puts it above everything that is not.
- Exploit odds: 1.6% in the next 30 days (EPSS).
- Severity: 8.8 HIGH (CVSS).
- Fix: a patch or advisory is linked.
Details
- Published
- Last modified
- Added to CISA KEV
- 2026-09-10
- Exploit probability
- 1.6% · EPSS, next 30 days
- Weakness
- CWE-306 · Missing authentication
- Record status
- Analyzed
Affected
- Mikrotik Routeros < 6.49.21
- Mikrotik Routeros < 7.23.4
- Mikrotik Routeros < 7.24.2
Attack profile CVSS 4.0 · 8.8
- Attack vector
- Network
- Complexity
- Low
- Attack requirements
- None
- Privileges needed
- None
- User interaction
- None
- Confidentiality
- Low
- Integrity
- None
- Availability
- High
Raw vector
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Is it in your code?
Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.
Read https://cve-list.com/agent/cve/CVE-2026-67277.md and follow it. Check whether this project is affected by CVE-2026-67277. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.
Fix and advisories
- https://cert.pl/en/posts/2026/09/vulnerabilities-in-mikrotik-routeros-actively-exploited/
- https://mikrotik.com/supportsec/september-2026-vulnerability/
References
- https://cert.pl/en/posts/2026/09/mikrotik-routeros-cve
- https://cert.pl/en/posts/2026/09/vulnerabilities-in-mikrotik-routeros-actively-exploited/
- https://forum.mikrotik.com/t/6-49-21-long-term-is-released/272802
- https://forum.mikrotik.com/t/7-23-4-long-term-is-released/272801
- https://forum.mikrotik.com/t/7-24-2-stable-is-released/272800
- https://mikrotik.com/supportsec/september-2026-vulnerability/
- https://npratley.net/reversing-mikrotiks-silent-patch-the-routeros-7-23-4-fix-they-wouldnt-explain/
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-67277