# CVE-2026-39042: MikroTik RouterOS denial of service in libumsg.so unflatten function

Source: https://junglewise.ai/threats/cve-2026-39042-mikrotik-routeros-denial-of-service-in-libumsg-so-unflatten  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-13. Updated: 2026-07-13  
License: CC BY 4.0 with a link back

CVE-2026-39042 · Severity: info · CVSS 0 · Published 2026-07-13

A security vulnerability has been identified in MikroTik RouterOS, the operating system used to manage MikroTik networking hardware like routers and switches. A remote attacker can exploit this flaw to crash the device's communication services, leading to a denial of service. This could disrupt network connectivity and management operations for affected organizations.

Technologies: [MikroTik RouterOS](https://junglewise.ai/threats/technologies/routeros). Vendors: [MikroTik](https://junglewise.ai/threats/vendors/mikrotik).

## Quick answers

**Is CVE-2026-39042 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-39042 being exploited in the wild.

**How severe is CVE-2026-39042?** Informational severity, with a CVSS score of 0, published 13 July 2026.

**Which products and versions are affected?** MikroTik RouterOS 7.21.x before 7.21.4, 7.22.x before 7.22.2.

**Is there a fix for CVE-2026-39042?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-39042 attacked?** It is attacked over the network, in an operating system.

**Am I affected by CVE-2026-39042?** Check whether you run MikroTik RouterOS at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

An integer overflow vulnerability exists in the core IPC library (libumsg.so) of MikroTik RouterOS. Specifically, the unflatten() function fails to properly validate input, allowing a remote attacker to trigger a denial of service (DoS) condition. The issue affects RouterOS versions 7.21.x (prior to 7.21.4) and 7.22.x (prior to 7.22.2). Exploitation occurs via the network and results in a crash of the affected service. Patches are available in RouterOS versions 7.21.4 and 7.22.2.

## Affected products

- MikroTik RouterOS 7.21.x before 7.21.4, 7.22.x before 7.22.2

## Timeline

- 2026-07-13: advisory
- 2026-07-13: disclosed

## References

- [https://mikrotik.com/supportsec](https://mikrotik.com/supportsec)
- [https://zakpatrik.cz/blog/finding-an-integer-overflow-in-mikrotik-routeros-core-ipc-library](https://zakpatrik.cz/blog/finding-an-integer-overflow-in-mikrotik-routeros-core-ipc-library)

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- [MikroTik RouterOS integer overflow in ipt_SAME module](https://junglewise.ai/threats/cve-2026-112158-a-weakness-has-been-identified-in-mikrotik-routeros-up-to-6-40-5)
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