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PatchSiren cyber security CVE debrief

CVE-2026-39042 MikroTik CVE debrief

A denial of service vulnerability exists in MikroTik RouterOS 7.21.x before v.7.21.4 and 7.22.x before v.7.22.2. The issue is caused by the unflatten() function in libumsg.so. This vulnerability could potentially allow a remote attacker to cause a denial of service. Limited information is available about this vulnerability, and additional review is necessary to understand the full impact.

Vendor
MikroTik
Product
RouterOS
CVSS
Unknown
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-13
Original CVE updated
2026-07-13
Advisory published
2026-07-13
Advisory updated
2026-07-13

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.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-39042 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-39042

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-39042 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-39042

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.