CVE-2026-67277: CWE-306 Missing authentication for critical function in Mikrotik RouterOS
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 v4.0
Score 8.8high
Affected software
Mikrotik
RouterOS
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability arises because RouterOS accepts a "related" btest connection prior to authentication of the primary session. An unauthenticated attacker can exploit this to start an IPv4 UDP test with the "random-data=false" parameter, causing the sender to transmit uninitialized data from a kernel packet buffer. Additionally, an unchecked inverted packet-size interval triggers an unsigned integer underflow, resulting in abnormally large fragmented output and the ability to restart the RouterOS kernel. This flaw is classified under CWE-306 (Missing Authentication for Critical Function). Mikrotik has addressed this vulnerability in versions 6.49.21, 7.23.4, and 7.24.2.
Potential Impact
An unauthenticated attacker can exploit this vulnerability to leak uninitialized kernel memory and cause a denial of service by restarting the RouterOS kernel. The vulnerability does not require user interaction or privileges and can be triggered remotely over the network, making it a significant risk for affected systems.
Mitigation Recommendations
This vulnerability has been fixed in Mikrotik RouterOS versions 6.49.21 (Long-term), 7.23.4 (Long-term), and 7.24.2 (Stable). Users should upgrade to one of these fixed versions to remediate the issue. No other mitigations are indicated by the vendor advisory.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- CERT-PL
- Date Reserved
- 2026-07-29T11:59:30.538Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6a9c76bdacd9273b49572669
Added to database: 09/05/2026, 20:08:29 UTC
Last enriched: 09/14/2026, 23:50:35 UTC
Last updated: 10/20/2026, 18:48:22 UTC
Views: 167
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