VDB-378184 · CVE-2026-39042 · GCVE-0-2026-39042

MikroTik RouterOS up to 7.21.3/7.22.1 Unflattener libumsg.so unflatten denial of service

CVSS Meta Temp Score CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.	Current Exploit Price (≈) Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.	CTI Interest Score Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
7.2	$0-$5k	1.82+

Summaryinfo

A vulnerability, which was classified as critical, was found in MikroTik RouterOS up to 7.21.3/7.22.1. This issue affects the function unflatten of the file libumsg.so of the component Unflattener. Executing a manipulation can lead to denial of service. The identification of this vulnerability is CVE-2026-39042. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability has been found in MikroTik RouterOS up to 7.21.3/7.22.1 and classified as critical. This vulnerability affects the function unflatten of the file libumsg.so of the component Unflattener. The manipulation with an unknown input leads to a denial of service vulnerability. The CWE definition for the vulnerability is CWE-404. The product does not release or incorrectly releases a resource before it is made available for re-use. As an impact it is known to affect availability. CVE summarizes:

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.

The advisory is shared for download at mikrotik.com. This vulnerability was named CVE-2026-39042 since 04/06/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 7.21.4 or 7.22.2 eliminates this vulnerability.

VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Type

Router Operating System

Vendor

MikroTik

Name

RouterOS

Version

License

commercial

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 7.5
VulDB Meta Temp Score: 7.2

VulDB Base Score: 7.5
VulDB Temp Score: 7.2
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AV	AC	Au	C	I	A
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳

Vector	Complexity	Authentication	Confidentiality	Integrity	Availability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Denial of service
CWE: CWE-404
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

0-Day	Unlock	Unlock	Unlock	Unlock
Today	Unlock	Unlock	Unlock	Unlock

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: no mitigation known
Status: 🔍

0-Day Time: 🔒

Upgrade: RouterOS 7.21.4/7.22.2

Timelineinfo

04/06/2026 CVE reserved
07/13/2026 +98 days VulDB entry created
07/14/2026 +0 days Advisory disclosed
07/14/2026 +0 days VulDB entry last update

Sourcesinfo

Advisory: mikrotik.com
Status: Confirmed

CVE: CVE-2026-39042 (🔒)
GCVE (CVE): GCVE-0-2026-39042
GCVE (VulDB): GCVE-100-378184

Entryinfo

Created: 07/14/2026 00:14
Changes: 07/14/2026 00:14 (55)
Complete: 🔍
Cache ID: 216::103