CVE-2026-39042 MikroTik CVE debrief

Who should care

Users of MikroTik RouterOS 7.21.x and 7.22.x should apply patches to prevent denial of service attacks. Additionally, security teams and vulnerability management teams responsible for MikroTik RouterOS deployments should review the vulnerability details and assess their exposure.

Technical summary

CVE-2026-39042 is a denial of service vulnerability in MikroTik RouterOS 7.21.x before v.7.21.4 and 7.22.x before v.7.22.2. The vulnerability is caused by the unflatten() function in libumsg.so. This technical issue could allow a remote attacker to cause a denial of service. The affected products include MikroTik RouterOS 7.21.x and 7.22.x. Users should review the official CVE record and NVD detail for additional information and apply patches from MikroTik to prevent denial of service attacks. The vulnerability has a medium defensive priority, and security teams should inventory affected systems, monitor for exploitation attempts, and review compensating controls for exposed systems.

Defensive priority

Medium

Recommended defensive actions

• Apply patches from MikroTik
• Inventory affected systems
• Monitor for exploitation attempts
• Review compensating controls for exposed systems
• Check relevant monitoring, detection, and logs for exposed assets
• Track exceptions and retest remediated assets
• Confirm whether affected product deployments exist in managed environments

Evidence notes

The CVE record was published on 2026-07-13T22:16:46.247Z and has not been modified since then. The NVD entry is currently Received. Limited source detail is available. Evidence from the CVE record and NVD entry indicates a denial of service vulnerability in MikroTik RouterOS 7.21.x before v.7.21.4 and 7.22.x before v.7.22.2, caused by the unflatten() function in libumsg.so. However, additional verification is required to confirm affected scope and severity.

Official resources