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CVE-2026-39042 Details

ANALYZED

This CVE record has been analyzed and enriched by NVDAPI.com as an independent party.

Description

An issue in MikroTIk (SIA Mikrotikls, Latvia) RouterOS 7.21.x before v.7.21.4 and 7.22.x before v.7.22.2 allows a remote attacker to cause a denial of service via the unflatten() function in libumsg.so.

Metrics

CVSS 3.x Severity and Vector Strings:

VolerionCVSS-B:5.3 MEDIUMVector:CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CNA: CISA-ADPCVSS-B:7.5 HIGHVector:CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://mikrotik.com/supportsec	[email protected]	Vendor
https://zakpatrik.cz/blog/finding-an-integer-overflow-in-mikrotik-routeros-core-ipc-library	[email protected]	ExploitRemedyTechnical Analysis

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-190	Integer Overflow or Wraparound	CISA-ADP

Affected Products

Product	Versions
MikroTik RouterOS	>= 7.21, < 7.21.4 >= 7.22, < 7.22.2
CPE cpe:2.3:o:mikrotik:routeros:::::::: Remediation Upgrade: 7.21.4moderate effort Upgrade: 7.22.2moderate effort Workaround:low effort Disable unnecessary services: /ip service disable telnet,ftp,api Enable strong crypto (disables weak SSH algorithms): /ip ssh set strong-crypto=yes Restrict management access to trusted IPs: /ip service set ssh address=192.168.88.0/24 /ip service set www address=192.168.88.0/24 /ip service set winbox address=192.168.88.0/24 Add firewall rules: /ip firewall filter add chain=input action=drop \ dst-port=22,80,8291,8728,8729 \ src-address=!192.168.88.0/24 \ comment="Restrict management" Keep RouterOS updated: /system package update check-for-updates

Product

Versions

MikroTik RouterOS

>= 7.21, < 7.21.4

>= 7.22, < 7.22.2

CPE

cpe:2.3:o:mikrotik:routeros:*:*:*:*:*:*:*:*

Remediation

Upgrade: 7.21.4moderate effort
Upgrade: 7.22.2moderate effort
Workaround:low effort
Disable unnecessary services: /ip service disable telnet,ftp,api Enable strong crypto (disables weak SSH algorithms): /ip ssh set strong-crypto=yes Restrict management access to trusted IPs: /ip service set ssh address=192.168.88.0/24 /ip service set www address=192.168.88.0/24 /ip service set winbox address=192.168.88.0/24 Add firewall rules: /ip firewall filter add chain=input action=drop \ dst-port=22,80,8291,8728,8729 \ src-address=!192.168.88.0/24 \ comment="Restrict management" Keep RouterOS updated: /system package update check-for-updates

Change History

2 change records found show changes

Date	Action	Recorded By
Jul 14, 2026	CVE Modified	CISA-ADP
Jul 13, 2026	New CVE Received	[email protected]