Required actionApply 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.
CWECWE-306
Descriptions
KEV: MikroTik RouterOS contains a missing authenticaion for critical function vulnerability which allows kernel memory disclosure and denial of service in the btest service.
NVD: 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)
Hunt RouterOS firewall logs for UDP traffic to port 20000 from untrusted sources, especially btest protocol packets with anomalous fragmentation or oversized responses. Monitor for kernel crash events in system logs following btest traffic.
Research details
Componentbandwidth-test (btest) service
PreconditionsUnauthenticated network access to the RouterOS bandwidth-test service on UDP port 20000; the target must run a vulnerable version of RouterOS (6.x below 6.49.21, 7.x below 7.23.4, or 7.24.x below 7.24.2); the attacker initiates a btest connection before the primary session completes authentication agent
Exploit notesNo public PoC exists for this specific CVE. The vulnerability is part of the broader MikroTrick chain (CVE-2026-67276 + CVE-2026-86060) which has a working exploit. For CVE-2026-67277 specifically, exploitation requires sending a btest connection before the primary session completes auth, then starting an IPv4 UDP test with random-data=false to leak uninitialized kernel buffer contents or trigger an integer underflow that crashes the kernel. The btest service is enabled by default and should be disabled on devices not requiring it.
SummaryMikroTik RouterOS contains a missing authentication vulnerability in the bandwidth-test (btest) service that allows unauthenticated clients to start an IPv4 UDP test before the primary session completes authentication, leaking uninitialized kernel buffer data or crashing the kernel via integer underflow. The vulnerability affects multiple RouterOS release branches and was patched on September 3, 2026. No public proof-of-concept exists for this specific CVE, but it was discovered alongside actively exploited flaws in the MikroTrick chain.
Tia coverage
First reported2026-09-03
When Tia's reporting first covered this CVE and whether a report claimed exploitation before the KEV listing. Lead-time deltas are measured from the exploitation report only — plain coverage is not exploitation intel. See the story links under Mentioned in for coverage detail.